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Fordson Tractors Discussion Forum

(2) 12V batteries in parallel too much??

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Robert

06-01-2004 10:16:49




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Still working on the 56 FMD and know that I will need to buy a battery here in the near future and with reading/hearing other people's cranking woes with diesels, I know I need to get a pretty strong one.

I was wondering though what damage would it do to have 2 12 volt batteries hooked up in parallel, just like you would if you were jumping it with another battery?? The battery box seems to be big enough, but just don't know if there would be any adverse affects of leaving it this way.

Matter of fact I looked at another FMD the other day hooked up in this manner, but nobody was around to talk to about the tractor.

As always, looking forward to the replies.
Thanks Robert

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m-ric

06-11-2004 21:03:07




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
Robert, I have a 55 FMD and I am running the cheapest battery I can find. I have not had any problems starting the tractor even in the middle of winter with temps in the 30's. I don't think it has ever spun over more than 4 or 5 times. If I was you I would be looking for a problem else where. M-RIC



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Mark

06-09-2004 09:08:02




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
There's absolutely nothing wrong with (2) 12 Volt batteries in parallel. A word of caution though. You need to make sure that once the two batteries are connected that you have a properly sized cable going from the batteries to the ground and to the starter solenoid. By putting the two batteries in parallel, you are increasing your Cranking Amps, which requires a bigger cable to properly carry the amps. Otherwise, you could end up with a surplus of cranking amps and no way to force it through a dinky 4 ga cable. Use good cable, preferably 1 ga or thicker and DO NOT USE the bolt on style battery terminal connectors. Make sure you have a good clean ground connection. If you use good thick cable with good connections, the old girl will really spin over with no trouble at all.

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Hal

06-15-2004 07:29:34




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to Mark, 06-09-2004 09:08:02  
The amount of amps being drawn thru the cables depends only upon the load and the battery voltage. As long as the load (starter, lights, accessories etc.) remains constant you could have 100 batteries in parallel, it wouldn't matter, you would still use the same proper sized cable as for 1 good battery.



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tony

06-13-2004 18:47:32




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to Mark, 06-09-2004 09:08:02  
Mark,

There’s a lot wrong with it. It creates a potentially dangerous condition, and you can have a runaway. (V2-V1)/R= I and (I*2)(R)= P

In real life two batteries are never at the same potential. So there is current flow between the two until on of the batteries is discharged enough for the voltages to equalize. If one of the batteries has a weak or shorted cell, there can be enough current generated between the two batteries to make one of them explode.

I read the web site referenced here and I just don’t agree that it should be done.

That’s why when you jump a car, they advise you not to connect the two batteries in parallel but rather, have one of the ground connections go to the chassis instead. This adds a small resistance and acts as a current limiter if the needs arise.

But this is a forum and we are supposed to discuss and get different views.

Tony

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Mark

06-15-2004 19:39:47




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 Re: Re: Re: (2) 12V batteries in parallel too much in reply to tony, 06-13-2004 18:47:32  
If this situation is so dangerous, why is it done on many big tractors? Battery explosions are caused by hydrogen gas (usually present when charging of discharged state) and sparks. That's a primary reason why they tell you when jumping a car, use a ground and not the negative post of the battery. They also tell you to hook up the dead battery first (presence of gas around a discharged battery). If somebody asks me "is there anything wrong with this?" I would say no. Open the hood of your diesel pickup and ask yourself that question (huh! Two 12V batteries in parallel).

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tony

06-17-2004 18:59:06




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 Re: Re: Re: Re: (2) 12V batteries in parallel too in reply to Mark, 06-15-2004 19:39:47  
You guys do what you want. I'm just telling you that it is not safe to design a system like that. If you need more current to start the system (given that all the connections are clean and tight), then you need to select a battery with a smaller internal resistance. No matter what two batteries you put in parallel, there will be circulating circuits generated from the two not being exacting the same.

This won’t occur when it is running with the alternator generating power, but rather when the system is at rest in a quiescent state.

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Hal

06-15-2004 07:21:48




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 Re: Re: Re: (2) 12V batteries in parallel too much in reply to tony, 06-13-2004 18:47:32  
The reason they tell you to connect one to a chassis bolt, etc. is to avoid a spark near the battery which might cause an explosion. For a short term situation like with jumper cables any parallel connection is fine, and the less resistance the better.



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CalG

06-08-2004 06:56:36




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
This topic appears to rage in the RV groups.
Link
This link speaks to some of the features of both types of connections. My reading is that it is a wash between them.

Regards

CalG



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CalG

06-08-2004 06:55:25




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
This topic appears to rage in the RV groups.

This link speaks to some of the features of both types of connections. My reading is that it is a wash between them.

Regards

CalG



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tony

06-08-2004 04:01:18




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
You never ever put two batteries in parallel. You are creating a very dangerous condition. Batteries can, will, and have in the past exploded. The two batteries will never be at the same potential and one will discharge into the other until a quiescent state is reached. The only thing that is limiting the current is the wire size between them.

If you want more capacity (amp/hours) you need to put two six volt batteries in series. If you need more power to spin the starter make sure you buy one with a very low internal resistance. i.e. a lot of cold cranking amps.)

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sandymac

06-05-2004 15:41:33




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
Robert, having run a power major for many years and counting!,,I cannot understand why anyone has to resort to more than 1 reasonable 12v battery!! If that wont start her, look for other faults like starter motor struggling, connections etc...A major in sound engine condition should start pretty sharpish anyway!!
Sandy.



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CalG

06-09-2004 07:18:43




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to sandymac, 06-05-2004 15:41:33  
Gosh

The E27n Major starts on the third or fouth pull even after sitting for several months. If I try to use the self starter, the engine motors over faster than the magneto impulse coupling can work it's magic. Then the spark goes out.

Progress!

Regards

CalG



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RayP(MI)

06-01-2004 18:38:56




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
General Motors used (still uses?) 12v batteries in parallel in their diesel trucks/suburbans/cars, etc. I am still running my 1983 pu that is set up that way. You need to start with a pair of new matched (same size) batteries, and keep them together for life. If you start with an unmatched pair, - not same rating, old/new, etc., the weaker one will drag the better battery down, resulting in premature failure of both.

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Mark Krzyzanowski

06-02-2004 21:40:10




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to RayP(MI), 06-01-2004 18:38:56  
That's true, and not about mis-matching batteries. True, 12 VDC is 12 VDC. But, floating a charge and recovery is not the same on a battery that has for example 24 plates and is rated at say 200 CCA and one that has say 30 plates and is rated at say 300 CCA. And a 200 CCA battery parallel to a 300 CCA battery does not give you 500 CCA, it gives you 300 CCA. The point is that the samller of the two will recover (charge) and discharge faster than the larger. You could actually over charge it while trying to recover the larger of the two, and overtax it during discharge. And age does matter as well. You would do yourself best to use like batteries in age, design, rating, etc. What you need to also be concerned with in running parallel is that your output duration is going to be increased, so your primary wiring should be able to accomodate this as well - 2 GA wiring won't hold up as well as 1 GA, and so on. Running parallel batteries? Not a bad idea, just make sure all components compliment each other, and buy yourself 2 new "like" batteries. And when replacing them in the future, repeat the procedure.

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CalG

06-02-2004 07:32:17




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to RayP(MI), 06-01-2004 18:38:56  
Don't worry about "matched" batteries. Any combination (Amp hour rating or physical size) will work fine. Don't mix voltage however). The batteries will put out, up to capacity, only what it is asked for when you start cranking.

It's like pouring water from two buckets. But make sure your cables and connections are first rate else you will bring on other problems. Heating at terminals etc.

Use of "good" batteries is always a smart choice unless you are trying to make problems for yourself. ;-)

CalG

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buickanddeere

06-07-2004 22:58:26




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 Re: Re: Re: (2) 12V batteries in parallel too much in reply to CalG, 06-02-2004 07:32:17  
You must be kidding? While lots of people who are either on the cheap or don't know any better. They mix new and old "V" belts, fluorescent tubes or batteries . "Mixing" always leads to inferior performance/durability. The theory and proof is beyond explaining on this site. It's easier to get two big sixes in series to work/charge than a pair of 12's in parallel. Best yet to just purchase one big honken 12V.

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Bob

06-01-2004 11:34:52




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 Re: (2) 12V batteries in parallel too much?? in reply to Robert, 06-01-2004 10:16:49  
The two batteries in parallel are just what the old girl needs. My neighbor and I both have our Majors set up that way, and have for years.

There will be no damage, and, in fact, having enough power to get the thing cranked over and started will be EASIER on the starter than a weak battery.



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Miles

06-01-2004 13:37:55




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 Re: Re: (2) 12V batteries in parallel too much?? in reply to Bob, 06-01-2004 11:34:52  
I assume this would have same effect as 2 x 6 volt in series?



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Hal

06-02-2004 11:59:07




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 Re: Re: Re: (2) 12V batteries in parallel too much in reply to Miles, 06-01-2004 13:37:55  
The thing is with 2 six-volt in series if one battery goes down or fails with a short it won't take the other one with it. Even so, if the batteries in series aren't somehat matched and you try to charge them both at the same time with a 12v charger, one may charge at a faster rate than the other. I have had good luck with 6v in series, but there are disadvantages to either setup. The best is if you can avoid multiple bats, just use the biggest, best quality 12v available and see how it goes. I often wondered if it would be good to install one of those switches like they use in boats to select either or both, or disconnect everything.

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Bob

06-01-2004 14:55:27




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 Re: Re: Re: (2) 12V batteries in parallel too much in reply to Miles, 06-01-2004 13:37:55  
When you put 2 6 Volts ins series, the amp-hour rating is equal to the amp hour rating of ONE of the batteries.

When you put 2 12 Volts in parallel, the amp-hour rating is doubled, so it's TWICE the amp-hour rating of ONE of the batteries.



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gahorn

06-01-2004 15:31:44




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 Re: Re: Re: Re: (2) 12V batteries in parallel too in reply to Bob, 06-01-2004 14:55:27  
Volts is like p.s.i. (pressure)
Amps is like gallons. Amp/hrs and Watts is like gallons per minute @ X p.s.i. (Well, not exactly, but it's good enough for the illustration.)

Two 6 p.s.i. (volt) batteries in series, boosts the second 6 to 12, ...but the gallons is the same. It's just at higher pressure.

Two 12 psi (volt) batteries in parallel still only put out 12 but they put out twice the gallons. (The fire is gonna be put out fast!...as long as it's not too far away.)

You really wanna do some work? Put two high-amperage batteries in parallel....and you get lots of gallons at high flow rates (pressure) and can do lots of work. (That's why pressure washer that have lots of g.p.m. do better than those that don't ...regardless of the pressure.)

Hope this helps put it in perspective.

A word of warning: Use of batteries in parallel requires they be evenly matched as to size, relative age, and capacity (amperage). (A new, good battery will discharge into an old, shorted one with disastrous results. Makes a helluva fire!)

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