12 Volt Power - Deuce with 3 or 4 batteries

[plym49]

Also, if I am not mistaken, the 12 accessories will see 24 volts since if they share the same ground.

You need isolation switches to make this work.

 

[Stalwart]

You need isolation switches to make this work.

Kinda defeats the purpose then, you can't draw power for a load and charge at the same time. What's wrong with "you can't get there from here?". I could devise such a circuit with multiple multi-pole switches but you still couldn't support a load and charge at the same time. If you're happy with a shortened battery life, just tap the grounded battery and be done with it. I don't care if you have to keep replacing batteries, it's not my money you're spending.

 

[rebel_raider]

Thank you for the information and advice, Stalwart. I was trying to be a cheapskate and figure out a way to get 12V without a converter or equalizer. I don't mind spending money, I just like to make sure there's not a "free" option out there somewhere.

There's nothing wrong with "you can't get there from here." I just meant you can't get 12V from 24V, without a converter or equalizer, without killing one battery eventually.

 

[Stalwart]

Actually, my last little bit wasn't directed at you Rebel. Simply offering that it can be done with some "isolation switches" doesn't help but further let people think it CAN be done on the cheap. Saying that, I've seen some people get away with $30.00 converters and to me, that seems cheaper that your proposed wiring with the busses, had that worked out.

To me there is nothing wrong with being frugal with your money, I'm of Scottish decent after all. I like simple clean and a good value. I'm just glad I didn't have to pay for that expensive converter in my truck, it came in it. If I hadn't found the new 100 A equalizer for cheap, I'd have gone with the convertor +battery, or at last resort the 2nd dedicated 12v alternator. My 12v demands are rather small, had they been large, the equalizer or alt would have been my first choice.

 

[plym49]

Actually, my last little bit wasn't directed at you Rebel. Simply offering that it can be done with some "isolation switches" doesn't help but further let people think it CAN be done on the cheap. Saying that, I've seen some people get away with $30.00 converters and to me, that seems cheaper that your proposed wiring with the busses, had that worked out.

To me there is nothing wrong with being frugal with your money, I'm of Scottish decent after all. I like simple clean and a good value. I'm just glad I didn't have to pay for that expensive converter in my truck, it came in it. If I hadn't found the new 100 A equalizer for cheap, I'd have gone with the convertor +battery, or at last resort the 2nd dedicated 12v alternator. My 12v demands are rather small, had they been large, the equalizer or alt would have been my first choice.

Hold on there, cowboy. When I mentioned the need for isolation switches, I made absolutely no mention of whether or not that would be 'on the cheap'. I was simply responding to the request for comments on the schematic that was posted. That diagram has short circuits and in any case will not do that intended.

If the solution also needs to be cheap, here's one: tap 12v off one battery. Every month, swap the batteries back to front., so you alternate between them.

 

[Stalwart]

WOW, swapping batteries every month, that's nice and elegant, convenient too. What if we need to tap off 20-50 A? How about a winch at 200-500A. You might not make it a month before killing the batteries, if you used the truck often. Please design this circuit where you can add isolation switches and make it work to provide 12v power for useful loads and properly charge the batteries without imbalance.

C'mon Sparky, educate us.

 

[plym49]

WOW, swapping batteries every month, that's nice and elegant, convenient too. What if we need to tap off 20-50 A? How about a winch at 200-500A. You might not make it a month before killing the batteries, if you used the truck often. Please design this circuit where you can add isolation switches and make it work to provide 12v power for useful loads and properly charge the batteries without imbalance.

C'mon Sparky, educate us.

???

I comment that the schematic was not going to work unless it included isolator switches, and you rag on me because switches cost money.

So then I point out that if someone was dead set on just tapping off of one battery, you can average the 'wear and tear' over both batteries by swapping connections. (Swapping wires is the cheapest 'isolator switch' on the market.) You are not happy with that, either, citing some scary 500 amp winch.

So exactly what are the parameters? I thought it was four batteries, 24 volts overall, with a 12 volt tap. Is that not correct? If not please illuminate us.

 

[Stalwart]

It's not just about MONEY! Using switches to isolate a battery allows for a TEMPORARY use, period. While providing 12V power, the isolated battery's aren't being charged. We are taking about a cost effective method of getting a 12v supply for accessories in a vehicle with a 24V system, it could be a radio or a winch or anything in between. Using a bunch of cheap switches would require you to activate them in an exact sequence or you fry stuff. Even using a series parallel switch, while possible, will cost you $150-200 and is only rated for intermittent duty.

You are missing on what kills the batteries when you imbalance them, it isn't the load itself but your 28v charging system. It undercharges the battery that has been tapped for 12V and OVERCHARGES the battery that isn't. A 5A CB radio won't cause a SERIOUS overcharge but even it, over time, will shorten battery life. I've seen this happen. It will even happen if you have one battery that is new and one that is slightly used previously. Don't you wonder why you don't just replace one battery in a 24v system but MUST replace them in matched pairs (same exact specs and brand), preferably from the same lot number? The answer is simple, they will become further imbalanced even if you swap them from time to time.

In the above situation you mention with 4-12v batteries, you could take 2 equal
batteries out of the 24V loop, discharge them in parallel and bring them back into a series-parallel situation, theoretically keeping the batteries in balance. The current would flow to the batteries in the lower charged state in the parallel part of the series-parallel configuration. STILL, you can't charge them AND draw power off them at the same time.

So what don't you still understand?

 

[plym49]

It's not just about MONEY! Using switches to isolate a battery allows for a TEMPORARY use, period. While providing 12V power, the isolated battery's aren't being charged. We are taking about a cost effective method of getting a 12v supply for accessories in a vehicle with a 24V system, it could be a radio or a winch or anything in between. Using a bunch of cheap switches would require you to activate them in an exact sequence or you fry stuff. Even using a series parallel switch, while possible, will cost you $150-200 and is only rated for intermittent duty.

You are missing on what kills the batteries when you imbalance them, it isn't the load itself but your 28v charging system. It undercharges the battery that has been tapped for 12V and OVERCHARGES the battery that isn't. A 5A CB radio won't cause a SERIOUS overcharge but even it, over time, will shorten battery life. I've seen this happen. It will even happen if you have one battery that is new and one that is slightly used previously. Don't you wonder why you don't just replace one battery in a 24v system but MUST replace them in matched pairs (same exact specs and brand), preferably from the same lot number? The answer is simple, they will become further imbalanced even if you swap them from time to time.

In the above situation you mention with 4-12v batteries, you could take 2 equal
batteries out of the 24V loop, discharge them in parallel and bring them back into a series-parallel situation, theoretically keeping the batteries in balance. The current would flow to the batteries in the lower charged state in the parallel part of the series-parallel configuration. STILL, you can't charge them AND draw power off them at the same time.

So what don't you still understand?

Hi Stuart - I don't understand how upset you seem to be over this. You are reading a lot into the simple comment I posted that that schematic would not work and the only way that schematic could come close to working is with isolator switches.

I am well aware of the principles involved. I have never challenged them or even commented on them in this thread.

Most folks who tap 12volts do so for accessories like that 5 amp load you mentioned. That is a relatively modest load and if you are going to run with one battery tapped, like dozens of folks do, then my advice to regularly swap the connections at the batteries is sound. That way you are not chronically overcharging one and undercharging the other. You are averaging the abuse, so to speak, not optimum but it will extend the life of the batteries and if you are replacing them in pairs anyway, well then you can understand the point.

I never recommended tapping 12 from one. I only suggested swapping the connections as a way of ameliorating a bad situation - after you wailed on me for having pointed out that that schematic would not work without isolator switches. Because of the $$$. If one does not want to spend money for a separate alternator or a power regulator or an isolator switch, then one is quickly running out of options.

Actually, there is one other approach that has not been mentioned that costs nothing and would always provide two good, solid 12 volt batteries. It is what was done in my old neighborhood when I was a kid. You steal a battery from someone's car. Then you wait a day or two. Now you go back to the same car. It has a brand-new battery in it. You remove the new one, and replace it with the old one you originally stole. Now you have a brand-new 12v batery. A MV requires you to to do this twice. Set up a regular schedule, and you will always have fresh batteries, so to blazes with the imbalanced charging.

 

[Stalwart]

OK, fine I got a bit pissy. If you understand all that YOU SEEM TO, why did you tell him he could fix it with some switches? You really can't, and you appear to understand that. Beyond those very light loads, just a couple of amps, it does kill batteries. Do you have any idea how many people have had battery problems doing this? Can we just nip this whole thing in the bud now?

Many years ago some guys on the early internet posted information regarding certain military vehicles that was either marginally true or totally UNTRUE and became gospel. I'd perfer we kept our information reliable as possible. I'd hate to see a guy spend lots of time and effort going down a dead end to only find himself with a burning truck, you know this can happen with the current available with 2-4 12V batteries.

I still don't understand the crap about the money. I told him a $30.00 converter would probably be cheaper than the wiring he was planning and your switches, which won't work as desired. I still think an equalizer (extra battery(s) optional) or second alternator + battery would be better, but for those on a budget a cheaper converter will probably do (also better with another battery, even a motorcycle dry cell). I certainly won't try to talk anyone into an EXPENSIVE converter like the failed one I have! You don't always get what you pay for, but you have to pay for what you get.

Goodnight

 

[plym49]

OK, fine I got a bit pissy. If you understand all that YOU SEEM TO, why did you tell him he could fix it with some switches? You really can't, and you appear to understand that. Beyond those very light loads, just a couple of amps, it does kill batteries. Do you have any idea how many people have had battery problems doing this? Can we just nip this whole thing in the bud now?

Many years ago some guys on the early internet posted information regarding certain military vehicles that was either marginally true or totally UNTRUE and became gospel. I'd perfer we kept our information reliable as possible. I'd hate to see a guy spend lots of time and effort going down a dead end to only find himself with a burning truck, you know this can happen with the current available with 2-4 12V batteries.

I still don't understand the crap about the money. I told him a $30.00 converter would probably be cheaper than the wiring he was planning and your switches, which won't work as desired. I still think an equalizer (extra battery(s) optional) or second alternator + battery would be better, but for those on a budget a cheaper converter will probably do (also better with another battery, even a motorcycle dry cell). I certainly won't try to talk anyone into an EXPENSIVE converter like the failed one I have! You don't always get what you pay for, but you have to pay for what you get.

Goodnight

Peace.

To answer your first question, I was simply answering his question, which was whether that schematic would work. It will not! And only could with switches. That was the extent of my response. I agree with your second statement - I tend to say the same thing a bit differently - you should never assume facts not in evidence. After some 10 pages of this thread, my contribution was to answer that one direct question and did not intend for anyone to read anything else into it.

As to your third comment, you are preaching to the choir, a good way to do this is with a converter/regulator, whether two batteries or four, or with a separate charging system. Personally, I run with a tiny (300 watt) 2-cycle 12vdc/120vac genset in the toolbox. It is a puny little thing but can always help recharge batteries (one at a time) or power a CB or cell phone charger should the need arise.

 

[DUG]

Dual alts just look really cool.............

http://www.steelsoldiers.com/deuce-modification-hot-rodding/62102-dual-alts-some-pics.html