Battery charging

[KG6EAQ]

So here is my deal, I want to put a deep cycle battery in the back with the radios to power them (Basically, I don't want to leave a radio on and have my car not start). What recommendations do you all have for an in vehicle deep cycle charger? One that I could hook up so that it only charges when the car is on. Could I just run a wire from the ignition sense side to the battery? I don't think I've ever seen a 12v batter charger that works off 12v . Thanks!

[HumHead]

It sounds like you are looking for an isolator. Basically, it is a diode bridge that allows the alternator to charge both batteries at once, while keeping the batteries isolated from each other.

You can find any number of varieties of the device. The more advanced models allow you to bridge the two batteries together if necessary, or to use the auxiliary battery as the main if the main battery is dead.

You should be able to find something suitable at most auto parts stores, RV supply houses, or someplace like JC Whitney. If you are willing to spend the money to do it right, I would heartily recomend Wrangler Power Products http://www.wranglernw.com/commerce/Show ... egoryID=24

As far as batteries go, once again, if you are willing to spend the money for the best, its hard to beat the Optima Spiracells.

If you are running your radio(s) off of the auxiliary battery, I would strongly suggest that you take the ignition sense power off of the auxiliary battery, through a relay connected to an ignition switched circuit in the vehicles main electrical system. There are (at least) two reasons for this:
1) You do not want to connect the two battery systems at any point other than the isolator. If the main battery is dead, the vehicle will pull power through any available path, namely your radios internal circuitry. Remember- given enough current, anything is a fuse!!
2) Some radios are very sensitive to differences in voltage between the main power and ignition sense lines. By running them off of a common source, you eliminate the risk of a radio going bonkers if one battery is running at a higher or lower voltage.

Good luck!

[KG6EAQ]

Thanks! You answered my question exactly! I'm off to the local Kragen to see what they got in isolators! I had no clue as to what I was even asking for, but now I know! Thanks again!

[chpalmer]

Boat supply houses have a little relay device that automatically switches on when the vehicle battery sees 13.8vdc. This makes shure that the starting battery gets its charge first. And you never touch the stock wiring as it goes between the two batteries using max 6 guage at least 6 feet long to achieve a little resistance. Kinda Cool actually!!!

[ptemplin]

I'm looking at a similar project to power the 12V fridge in the back of my Excursion. I'm planning to do the following:

One or more Optima blue top batteries to power the fridge.

Kussmaul Battery Saver HO. This provides up to 10A on each of two completely separate circuits if 120V is supplied to it, thereby relieving the load on the batteries (and therefore the battery charger also). I'll be able to stick my cell phone and rechargeable flashlights on one half of the unit (connected to the vehicle batteries) and the fridge and possibly some computer accessories (connected to the auxiliary battery) on the other half of the unit.

Kussmaul Auto Charge 11 HO. This provides up to 20A of current to recharge up to two separate battery groups, with the current to each proportionate to the level of discharge. Since the fridge draws 4A continuous, it should be able to recharge the battery in about 1/5th of the time that the fridge was running with the engine off.

Kussmaul Auto Isolator. This is a solenoid for tying together two battery systems for charging while the engine is running. I really like the thought of this unit, as it doesn't use diodes. Diodes cause a 0.7V drop, which prevents the batteries from getting a full charge. The control circuit on this unit also allows the auxiliary battery(ies) to assist with starting if they're strong enough.

Kussmaul Auto Eject. Quite simply, it's a receptacle to be mounted on the vehicle to automatically disconnect the 120V power as soon as the key gets to the start position.

I'd love to hear comments from any of the experts out there if I've got the wrong idea on any of this. I'd also be willing to answer questions from others.

See http://www.kussmaul.com for what they've got.

[ptemplin]

I wanted to clarify some details on my previous post:

1) My Excursion is diesel, so I already have (and need) two batteries to be able to effectively start it.

2) I want the fridge to be able to run on its own, without affecting the startability of the vehicle, in open parking lots. Hence my motivation for a deep cycle battery. I want to be able to ignore the fridge, and have it work as best as possible. Here in San Antonio, it's so convenient to grab a bottle of water (the fridge holds at least 24), and it'd be real nice if they were reasonably cool.

3) With a little work and a careful eye on the 120V ammeter, I hope to modify the circuitry to allow a winter mode. Winter mode would power the block heater off the shore line (obviously), and disable the fridge unless the key was on.

[apco25]

We use the kausmaul chargers on the FD rigs, both trucks and regular cars and ambulance packages. They do an excellent job of charging the batteries, are high quality and are easy to install. I don't think the public safety user with a his POV needs one unless you have very high battery drain issues. I have quite a bit of radio and warning gear in my truck, but everything is relayed and ignition controlled to prevent problems. I see no need to have radios,lights or anything on if I'm not in or near the vehicle while its running.

I do plan on installing a dual battery setup, but I'm having excellent results using a heavy duty 1100 CCA battery charged by a 200 amp high output alternator. Might even install a ignition key overide. I do like their load management system. That might be a cool thing for the vehicle to prevent load dumping back into the battery and alternator.

[Tom in D.C.]

I like that thingie that spits the connector out of the vehicle's charger power outlet when the engine is started, and I wonder how many FD's (especially houses where the trucks sit for days at a time without being started) use this device.

Tom, W2NJS
...in D.C.

[alex]

Tom -

We have those up here. Most of the ambulances that I ride on (with one exception) do not have auto eject. Almost every fly car I've seen uses them.

Just don't be standing near a freshly installed one when you just get it back from the installers... those things fly out of the sockets and can leave a mark .

One of my friends made the mistake of standing over one when someone started the vehicle. It had quite comical results for those of us who witnessed the event.

Very neat, simple toys.

On on ambulance I ride on the plug is mounted in such a way that you can't open the driver door without pulling out the plug first. This was somewhat smart, but you can tell where it has hit the door when someone forgets to unplug it.

-Alex

[jcobb]

All the above are excellent ideas. One caution on the deep-cycle batteries though. We use them on our communications van as it sits for a while with no shore line, so we want deep-cycle to handle the load until we get the generator going or a shore line hooked up.

But I used a deep-cycle dual battery set up in my POV, and did not have good luck with it. Seems like the deep-cycles want just that - charge and then run them almost flat. I was charging mine while the vehicle was running (along with the regular battery) with an isolator. I was not pulling enough juice to run it down enough to warrant all the charging it was getting. So the bottom line was that I got about a third of the life out of the deep-cycle as I did when I just added a second vehicle battery to the set up.

Of course, based on your usage, it might be worthwhile to go with the deep cycle. I have had no experience with the Optima, although I have been looking at them for my POV dual-battery set-up (the regular ones, though, not the deep-cycle).

Jack

[A10382]

Another poster had suggested you look at what marine dealers sell.

Deep cycle batteries are a bit different than the OEM ones. The deep-cycle battery doe sneed to discharge quite a bit between charges to insure a long life. It's not the 'memory' problem typical of nicads. Its more a function of the design of the battery's cells...

The typical dual (or even triple) battery setup for a sailboat may fit your bill.. It's designed to always have one fully charged battery to start a recalcitrant deisel.. and allow the other battery(s) to be used for lighting, refrigeration, TV, radio, etc... and discharge almsot completely.

They usually has a large knobby rotary switch for manual override or swapping the function of the two batteries. You do need to run the #6 or #4 cabling to the switch or it's remote control box and then to the batteries. This lets you then alternate which deep cycle battery gets to run down before being charged. Alternating the batteries assures full life from both.

Doinf something as snazzy as a triple battery setup with charge monitoring guages and even automatic control will NOT be cheap. This is definetly not Pep-Boys parts-store pricing.
---

Another thing to keep in mind: Unless you use truly sealed batteries (and Marine deep-cycles ones are usually not sealed) , they will be giving off hydrogen and some other nasties while being charged! Good ventilation in the battery compartment is the order of the day to prevent you vehicle from possibly becoming the "Hindenberg II".

[ptemplin]

I appreciate everyone's insights into this. I'm envisioning two (mostly) separate systems:

1) The "regular" vehicle electrical system, for starting, lighting, and ignition. My existing communications will remain connected to the vehicle system, as it's all connected to key-on circuits and won't present a measurable draw (except for the keepalive circuits to some of the Maxtrac radios). The only measurable key-off draw will be the rechargeable flashlights.

2) The "fridge" electrical system. One Coleman 12V thermoelectric fridge which draws 4A continuous. A 50AH battery will therefore last about 12.5 hours in an open parking lot. Therefore, any time away from the shore line will result in a good, measurable draw to help exercise a deep-cycle battery.

I anticipate tying the systems together through a solenoid isolator from a reputable firm, as well as installing a shoreline connection that will recharge the batteries and take over powering the fridge. Some thought will need to go into a winter mode, as I don't think I'll have enough current left over to power the 1kw block heater and feed the battery charger and 12V supply to the fridge, but I'll worry about that separately.

[nmfire10]

... I don't think I'll have enough current left over to power the 1kw block heater ....

[StanComm]

One thing to remember with any two-battery system is this... always make sure that one battery is connected to the alternator.
On an old fire engine equipped with two batteries, there was only a "Battery A, Battery B" switch, with all the distribution coming from the alternator. Every so often, one of the mic cords would tangle with the toggle handle and switch the battries with the engine running. POOF, the PNP germanium output transistors in the siren/pa amp would go... expensive buggers even in '96 dollars.
I tried to talk them into one of those isolators but they wouldn't spring for the cash.
Moral of the story... an unloaded alternator can produce more than 100 volts during the changeover... most transistors don't like that!
Stan

[RKG]

Two guys have asked questions that are far more complex than they realize and, I regret to say, some of the advice given here is not good. I hope it isn't too late.

1. Stay away from isolators. They are simply a diode bridge, and like all diodes, they have a forward voltage drop of about 0.6V. They can be safely used only in a specialized situation in which the charging equipment (in a vehicle, the alternator and regulator) "sense" voltage by a remote lead downstream of the isolator. In a vehicle, the alternator regulator "sense" on its own output (known as "machine sensed"). This means that the batteries downstream of the isolator will never see more than 0.6V less than the regulated voltage, which means that they will become chronically undercharged; ultimately, they will sulphate and die.

2. It is exactly wrong to say that deep cycle batteries need to be deeply cycled from time to time to preserve their life; to the contrary, deep cycling (below 50% of nominal capacity) will drastically shorten life. The usual rules are: never discharge more than 50% of nominal capacity; don't try to recharge more to than 85% of nominal capcity (if running an engine for charging only), as it will take forever; and if the batteries are flooded cell lead-acid type, equalize periodically.

3. A vehicular "charging" system (alternator and regulator) is a poor battery charger; it wasn't designed to charge deeply discharged storage batteries, but rather to act as a battery eliminator, carrying the DC loads while the engine is running. Since these operator on a fixed-voltage voltage-regulation principle, their voltage has to be quite low (about 13. as not to cook batteries during long vehicle runs, and at 13.8 a discharge battery will never be charged. Correctly charging a deeply cycled battery requires a multi-stage charger (either 110V driven or a multi-stage alternator regulator): Stage 1 is "bulk," where the charger runs at full capacity until the battery terminal voltage is 14.4, corrected for temperature, for a stated time; Stage 2 is "acceptance," where the charger switches to voltage-regulation at 14.4, corrected for temperature, until the charge rate drops to 2% of nominal capacity for a stated period; and Stage 3 is "float," at which point the charger switches to voltage regulation at a low voltage (13.5, corrected for temperature) that will not cook the batteries but will carry DC load.

4. The notion that a 50 AH battery will out 4A for 12.5 hours is not correct. The rated capacity of a battery is its so-called "20-hour rate," and is valid only for a load equal to 1/20th of nominal. Thus, a 50AH battery, in perfect condition and assuming it to have been honestly rated, will put out 2.5A for 20 hours, at which point its terminal voltage will be 10.5 and it is considered to be dead. On account of something called Peukert's Equation, battery capacity drops drastically as load exceeds 1/20th of nominal capacity. And remember, you can't take more than 50% of the nominal capacity out of a deep cycle battery without killing it.

5. There are only two ways to effectively put a second, deep-cycle battery in a vehicle, and both are expensive. Method No. 1 involves a second alternator, rated at a high capacity and controlled by a multi-stage external regulation. See Hehr Power Systems for the Alternator, and Heart (formerly Cruising Equipment Co.) for the regulator. Both the vehicle system and the auxiliary system are completely independent and are never wired together. Method No. 2 involves using a 120V DC alternator, which powers a 12V-to-110V inverter, which then powers a battery charger, which then charges the auxililary battery (and carries its load).

6. I didn't take notes on the prior posts and my memory is fading, but it is not correct that you can simply take a garden variety battery charger of, say 10A rating, and assume that it will replace 20A of discharge in two hours. First, the "charge efficiency factor" that applies to all batteries requires that more AH be put back into the battery than were taken out in order to charge it. Second, your garden variety charger is most likely a fixed-voltage ferroresonant type, and you will see that its charge rate drops drastically after about 20 minutes of charging, as the battery's terminal voltage has increased to virtually the same value as the charger's fixed voltage.

7. Sorry for the lecture; I've designed a number of high-capacity DC systems for sailing yachts, which run their entire load off large banks of deep cycle batteries and then expect to recharge them once a day (in an hour or less of engine or genset running). For a good discussion of the issues involved, explore the various technical papers published at the Cruising Equipment website, http://www.cruisingequip.com.

[ptemplin]

RKG, I appreciate your insights, and I've definitely learned something. However, if you check my first reply to this, you'll see that I specifically pointed out that the isolator that I plan to use does not contain diodes.

In your post, you say that an alternator and regulator is not a good charging system, and go on to indicate that certain voltage levels are necessary. However, you don't explain why an alternator and regulator are not suited for this. I'd even go so far to say that you say that the battery should be charged on something besides an alternator, or at least not part of the rest of the vehicle's electrical system, but you don't explain why.

Can two 50 AH batteries output 4A for 25 hours? Answering a simple question like that (by suggesting that a second battery be added, to get below 1/20th current flow out of each battery) would have been helpful.

You describe two ways to charge deep-cycle batteries, yet don't explain why they can't be charged in a vehicle. You also didn't take the time to look at the variety of chargers - I intend to use something much better than a garden variety charger, and clearly outlined that in my post.

I appreciate your information, but some acknowledgement and interpretation of the information already presented might have done wonders for enlightening you on the planning already conducted, as well as lightening the tone of your post.

[RKG]

Let me try to be more helpful.

Can 2 50AH batteries put out 4A for 25 hours? No.

Two 50AH batteries, wire in parallel, make a 100AH battery. At 5A load, the battery will put out 5A for 20 hours and then be dead. Since it was discharged 100%, it will never recover its full capacity; after the best charger in the world has quit, it will now be something like an 80AH battery, and after 4-8 of these cycles, it will refuse to accept any charge and be a paperweight.

In theory, the inverse of Peukert's Equation suggests that at a 4A load, the capacity of a nominal 100AH battery would be more than 100AH, since 4A would be the same as a 25-hour load. In real life, though, it doesn't work that way. Some makes of batteries might exhibit a small increase (less than 5-10%); most would not. At best, you'd get to something between 20 and 21 hours before the battery fell to 10.5V and died.

Actually, in either case the installation would fail, but for an entirely different reason. Most 12V refrigeration compressors will lock themselves up if voltage falls below about 11.5V. This would happen, I'd estimate, about 11-12 hours into the hypothetical run. If the compressor is of the hermetically sealed type, it cannot be repaired.

If you want to take out 50 AH between charging, your battery bank should be equal to 150-200AH. That way, it won't be discharged below the 50% point and you won't have to take the time to charge it to greater than its 85%-90% point, and with good batteries, you should be able to get 500 cycles, give or take.

Can an alternator and regulator be used for charging deeply cycled batteries? Yes, but only if they are the right kind of alternator and regulator.

The rate at which a charging device can put current into a battery is a function of the difference between the voltage of the charging unit and the voltage of the batteries. If the difference is greater, the current flows faster. If the difference is slight, little current flows, and if the difference is zero, no current flows.

The voltage of a 12V battery under load will be something between 12.5V and 10.5V, depending on how much load and the state of charge of the battery. However, once the load is removed and a charging source is applied to a 12V battery, its terminal voltage will very quickly rise to 13.2 to 13.5 volts, after only a few minutes of charging.

The alternator in most vehicles has an internal regulator (which means you can't change it or bypass it with a good external regulator), and the regulator is a fixed voltage type. Because the voltage is fixed, the manufacturer has to make a compromise. At 14.5V or so, the regulator would allow the alternator to run wide open until the battery had reached about the 90% of capacity point. However, if you kept on driving for a half an hour, the battery would begin gassing at a high rate, boil off its electrolyte, and be killed. Moreover, in a vehicular application, you don't need much battery charging. Assuming your starter takes about 200 amps, it only runs for less 5-10 seconds before the engine is started, and the battery draw is less than 1AH. After the engine is going, the alternator carries the DC load, and the battery does nothing. And we have to design the system so you can drive for 10 hours without killing it. So we set the fixed regulator voltage at something like 13.4 or 13.5; this will charge the tiny amount necessary to put back the starting load, and it will then "float" the battery all day without overcharging it. However, if the battery has been deeply discharged, the 13.5V fixed-voltage regulator will quickly shut down the alternator because, although discharged, the battery terminal voltage will quickly rise to 13.5. If the alternator output voltage and the battery terminal voltage are the same, no current will flow into the battery. Even if it is discharged.

So what I said - or at least what I intended to say - is that the alternator/regulator installations that are universally (and properly) found in motor vehicles can't be used to charge batteries. They weren't designed to charge batteries. They aren't needed to charge starting batteries. And if you did design them to charge batteries, they'd quickly kill the starting battery in a vehicle installation.

How to charge a deeply cycled battery: you can do it by using the engine of an engine-driven vessel, but only if you use a high capacity alternator (such as those sold by Hehr Power Systems or Balmar) and a multi-stage regulator. You can also do it off line current, but you must use a multi-stage charger, sometimes called a "smart charger." Examples are the StatPower line and the Heart Interface, both of which are quite expensive. The chargers you mentioned are fixed-voltage, ferroresonant chargers; their output drops precipitously as battery voltage increases, and they won't put out their rated value for more than about 10 minutes. I hate to say it, but they are garden variety, and the industry is able to sell ferroresonant chargers only because people don't know any better.

Isolators without diodes? So far as I am aware, there is no such thing. Indeed, I don't believe the laws of physics would permit a solid-state device that performed a diodic function (i.e., current can flow in only one direction) without a forward voltage drop. To do that, you need an electro-mechanical device, and there are, as one other fellow mentioned, an alternative to isolators, which are known in the marine trade as "combiners." What they are are continuous duty solenoids connected to a circuit that pulls the solenoid in if the terminal voltage on either output pole exceeds 13.1 for more than 20 seconds and drops the solenoid out if terminal voltage on the higher of the two output poles drops below 12.5 for more than 20 seconds. They are the effective equivalent of manually switching a two-bank battery switch to the "All" position. But in a vehicle, you never want the vehicle battery and the auxiliary batteries connected, because you don't want the vehicle alternator to see the auxiliary batteries and you don't want the auxiliary charger to see the vehicle battery. The most reliable make of combiner is a device call "Pathfinder" by Blue Sea Industries (about $250), though West Marine has a line for about half that if you are willing to replace the device every four or five years.

Anyhow, I don't want to preach, and I don't want to try to convince you to accept my expertise. I'll gloss over the fact that I have consulted for a number of television outlets trying to accomplish what you are aiming for, in order to run their microwave, editting, and "field cam" functions, and the only two types of installations that have ever worked are the two I described. The TV industry has a long history of failed installations, much like the other person on this thread who posted that he had had bad luck. The reason his installation failed is that his deep cycle batteries were chronically undercharged. When that happens, the lead paste turns to lead sulphate, a rock-hard crystal that destroys a portion of the positive plates. With each cycle, less and less of the battery's capacity was replaced; the degree of sulphation increases; and eventually there is so little working area left to the positive plates that the battery won't take any charge.

However, I do hope that, before spending any money on something that won't work, you take the time to study the subject. There is an excellent book (I forget the name, but the author is Nigel Calder) on the subject. However, the fastest way to get a handle on this complex subject is to peruse the excellent white papers in the Cruising Equipment website. Before being acquired by larger companies (first Heart, then Xantrex), Cruising Equipment was a small outfit manned by a bunch of very knowledgeable people (they are still there, by the way) who invested a good deal of effort in preparing educational materials on this subject. That way you'll be able to make your own informed judgments, which is always better than accepting what someone else says at face value.

Good luck.

[ptemplin]

You'd be a lot more believable if your posts could agree with each other. In your first post, you spoke about the AH rating like this:

Thus, a 50AH battery, in perfect condition and assuming it to have been honestly rated, will put out 2.5A for 20 hours, at which point its terminal voltage will be 10.5 and it is considered to be dead.

In your second post, you spoke about the AH rating like this:

Two 50AH batteries, wire in parallel, make a 100AH battery. At 5A load, the battery will put out 5A for 20 hours and then be dead. Since it was discharged 100%, it will never recover its full capacity...

"Considered to be dead" and "discharged 100%" are quite different metrics, not to mention that if battery manufacturers claim that a battery is a 50AH battery, they wouldn't claim it if it renders the battery unrechargeable or not very reusable.

Also, you didn't catch the part about the fridge being thermoelectric. There is no compressor, there is no cycling. It's a 4A draw continuous.

As far as isolators without diodes, perhaps the device I'm thinking of is in fact a combiner. However, my original message contained a URL which allowed you to research what I was saying (or not saying, since I knew their website said it for me). The device I'm looking at does not conduct voltage sensing for "20 seconds" like you describe. Instead, it ties the battery systems together after the engine has started (or during starting if the auxilliary batteries have sufficient voltage to be of help), and disconnects them at engine shutdown.

[RKG]

I'm trying to be helpful, and you apparently just want to fight. I don't, so I'll sign off with a couple of observations:

1. My two definitions of AH rating are entirely consistent. The battery manufacturer is not representing by an AH rating that youc can regularly take that many amp-hours out and keep the battery working. Rather, he is saying that the battery meets the industry definition, which is that if you load it to 1/20th the rating, it will run for 20 hours before dropping to 10.5V. It is analogous to the "breaking strength" of a piece of rope; the manufacturer isn't saying that you should put that much load on it, because if you do, it will break. The manufacturer assumes that you know what everyone else knows in this field, which is that the useable capacity of a deep cycle battery is about 35% of its rated AH capacity (in the region between 50% depleted and 85% depleted). I don't know what you mean by the term "metrics" in this context; my statements are identical and both true.

2. If your refrigerator is a solid state device, a similar (but even more gating) principle applies: most solid state devices will fail (fatally) if their applied voltage falls too far below nominal voltage; that is why, for instance, that most solid state radios include circuits that will turn them off if voltage gets to about 11.2 to 11.5V (assuming they are rated for a nominal 12V input power). It is to protect the solid state devices. So your ice box will either shut down protectively or shut down fatally at the point I indicated, in the hypothetical described.

3. The waiting periods for combiner cycling, which are known as hysteresis, are there to protect the combiner from rapidly (and continuously) turning on and off. If you have a combiner designed with zero hysteresis, you should take it back, as it is poorly designed and will quickly fail. All combiners use solenoids (a form of heavy-duty relay), and all relays have a finite life in terms of number of switch cycles. If, however, you're saying that the solenoid in this device is manually switched, then it is just a battery switch. In all events, combining the starting battery (and it's associated charging equipment) and the deep-cycle battery (known in the industry as the "house" battery or bank of batteries) (and it's associated charging equipment) is a bad idea, for the reasons I set forth.

My sense is that you are taking offense because reality doesn't square with your expectations. I'm sorry about that, but I can't change reality. I gather you haven't taken the time to learn about this complex (but fascinating) subject by reading the excellent materials to which I've directed you. I've invested a fair amount of time trying to be helpful, and if you don't comprehend (and appreciate) that, please save us both some time by not replying.

Out.

[ptemplin]

I appreciate your willingness to step forward and provide insights. Your original post and your followup replies suggest that you're quite knowledgeable, particularly from a marine application. My concerns are as follows:

1) You didn't appear to take the time originally to match your post to the applications described, as you hadn't read the simple blurb about what kind of fridge I have, you didn't seem to read the short segment about the "isolator" (or whatever it is, in your vocabulary), and other details. I'm glad you're an expert on marine power, but I don't think my Excursion will float, and I think there's a different set of applications present.

2) You often said that a given device was a poor choice for an application, and "defended" that by saying that certain voltage levels were required. However, you rarely said specifically that a given device did not provide those levels, or even what levels it did provide. For example, car batteries often last 4-8 years. How can an alternator/regulator be such a poor charger if the batteries last so long, battery chargers aren't normally included from the factory, and folks don't need to plug in their cars at specified intervals?

3) Through three posts, I've managed to learn that a deep-cycle battery can supply up to 1/20th of its rated capacity for up to 20 hours. Attempting to run it at a higher load or for longer is apparently a recipe for disaster, or at least a dead battery. I hope I've learned that correctly. However, for someone as knowledgable as you, it took a while for me to learn that (it wasn't clearly stated).

4) Your online reference takes me to Xantrex Technology, not Cruising Equipment, where I can only find products, and not many direct references to battery charging, etc. I've already read a lot of product information, which is where and how I learned what I learned already.

[RKG]

I can't resist, though I should.

If you've "learned" that you can take 1/20th of a battery's rated capacity out for 20 hours, then you haven't learned much. You can do that only if you're willing to kill the battery, just as you can load a piece of rope up to its breaking strength only if you're willing to break it. Fine for laboratory testing; won't work for an operating system.

Car batteries (that is to say, starting batteries, whether in a car, truck, boat, or something else) last for years because (as I explained) they are never discharged and are immediately floated. Equating the duty, design or performance -- or charging requirements -- of a starting battery to those of a deep cycle battery is like equating a 2d finish nail to a half-inch lag screw. You can do it if you insist, but whatever you build will rather quickly fall down.

Xantrex is now the parent company of both Cruising Equipment Co. and Heart Co. The white papers are on that web site, or at least they were yesterday.

The principles that govern heavy DC system design are the same regardless of whether the application is marine, large-scale backup power, RVs or comm vans. Which is why the equipment available for all those applications is the same. For what its worth, I have a degree in electrical engineering and have designed and built systems for all four of those applications.

I have also taught this subject in classrooms, which experience has taught me that some folks can't be taught.

S'long.

[ricciticcitembo]

Hmmm.... My two cents on this subject would have to be....

that first of all i want to back up RKG as far as bulett proof commercial/industrial/high power installations is concerned is 100%
correct based on my experiances and observations in the field of backup power management as well. It is a similar concept to my immediate first thoughts on how to mount a pile of spectras in a very small enclosed tight space and having them operate at 100% with no compromise on performance simultaneously and last another 10 years with minimal maintainence, given all the knowledge that i have accumulated over the years.

However, I would in fact argue that this is in fact NOT the original intention of the guy who wanted to install a small 4A
ThermoElectrically cooled styrofoam lookin "Refrigerator".
You will do just fine as you suggest with your External 120 Vac
Ferroresonant Charger/Vehicle Battery isolator/SpiraCell or Deep
Cycle Auxilary Contraption long as you have a device that will SHUT - OFF the load (refig) once the battery has been depleded to its 50% capacity level. This will help insure that the battery has an
acceptable life expectancy. Also I would not worry about any voltage drops that will inevitably occur , in so far as damaging the
Thermoelectric cooling element. It has been my experiance that Low Volt or Hi Volt for that matter WILL destroy Hi Current using
Transistor devices/or computer related equipment as mentioned,
however we used to vary the temperature by changing the voltage
to the TE Module, so i suspect even 8Volts wouldn't harm it any.
The cooling fan on the heatsink (if it has one) however is a little different, and it depends on exactly what type and model Fan it is and whether or not it will get killed by voltage tolerances . It should be OK though. Incedently the local Saab dealership sells "refrigerators" for only 200 dollars or so. (can't believe how cheap! for a Saab ANYTHING at the Dealer) And they say it can only
be used when the vehicle is running. But what do they know??


Good luck, and It looks to me that you are taking very resonable precautions considering the fact that your not trying to run High Power things with the Power Off, I'm sure you will be satisfied with your project.
Be sure to let us know how nice it is to have cold Drinks next Summer!!!!