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Can a car have too much battery? #5443481 05/31/20 07:13 PM
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wings&wheels Offline OP
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I would think no, but I remind myself that I am a hobbyist. One w/ 30+ years of owning and maintaining odd cars, but still an amateur....

A question for the experts who understand charging systems.

I helped a friend restore a mid 50's car with a 12v positive ground system that originally had two small 6v batteries wired in series. The car has a rebuilt original generator, 30 amps output I believe. My friend decided that he wanted more reserve, planning on two larger (group 24) 12v batteries, obviously wired in parallel. This is a very for cry from what the car had originally.

My question is can battery capacity ever be too much for the available charging power to the point where it could impact generator life, maybe affect the external regulator? I can't see it as in normal operation, the generator would recharge the batteries from starting and supply the vehicle as normal, but if the batteries are severely discharged, could the draw of charging two much larger batteries damage the generator? I would think that the generator has a maximum capable output and that is it, but maybe it could be damaged by having to run at max output to 'fill up" the greater capacity battery suite. Not much out there on this...


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Re: Can a car have too much battery? [Re: wings&wheels] #5443493 05/31/20 07:32 PM
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eljefino Offline
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Why would the battery be discharged?

The generator makes all the power the car needs to run, either now, or paying off a deficit.

The textbook reason for a bigger battery would be starting in the cold, if the car is cantankerous for whatever reason and doesn't catch the first time.

A generator runs all its power through its brushes, which are a wear item. Running more would wear them out faster. But, again, why are we running more, unless some is being "stolen" or "lost" from the electrical system or battery in some way.

So if someone leaves their headlights on and gets a jump (or a push start), the bigger battery runs more of a deficit. Think of it as a higher credit limit. Since these cars could be push started, why bother with a huge battery?

Re: Can a car have too much battery? [Re: wings&wheels] #5443495 05/31/20 07:34 PM
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Originally Posted by wings&wheels

My question is can battery capacity ever be too much for the available charging power to the point where it could impact generator life, maybe affect the external regulator?


Assuming everything properly functioning, in a single word, no

I doubt you will find much on this because a generator can only create energy based on the excitement of the field and the size of the windings- It cant "over produce" itself and the discharge state of the battery have no bearing on that capacity.

Re: Can a car have too much battery? [Re: wings&wheels] #5443497 05/31/20 07:38 PM
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wings&wheels Offline OP
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Thanks both. That is my thinking.

If the batteries were severely discharged, the generator would charge and supply the vehicle at its maximum until the batteries were at their normal state. Maybe it would run at that higher output longer (than with the small originals), but would operate normally.


'05 Lotus Elise S/C
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'74 Triumph TR6
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'01 Porsche Boxster S (mostly Wife's...)
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Re: Can a car have too much battery? [Re: wings&wheels] #5443507 05/31/20 07:54 PM
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eljefino Offline
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The external regulators back then were a vibrating relay thingie, so if the battery were "thirsty" the generator would be at 100% and the regulator wouldn't be doing much. Only concern would be welding the contacts closed, but I don't know enough about failure modes of the primitive things to know if that was any more likely.

Re: Can a car have too much battery? [Re: wings&wheels] #5443542 05/31/20 08:52 PM
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Some of those systems had a current regulator relay as well, so a severely discharged or shorted battery wouldn't overload the generator.

Re: Can a car have too much battery? [Re: wings&wheels] #5443564 05/31/20 09:22 PM
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Yes the older generator charging systems can be over stressed when under full load continuously. Under normal load the regulators were a wear item as I remember them which is why so many older vehicle owners upgrade to alternators.


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Re: Can a car have too much battery? [Re: wings&wheels] #5443577 05/31/20 09:43 PM
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I had a '61 Buick with a generator. I wasn't very impressed with the size of the power wire connecting the generator output to the battery.
I think it was 6 feet of 10ga or 12ga; seemed small by today's standards.
I put a parallel 10ga conductor in, to lower resistance.

Re: Can a car have too much battery? [Re: wings&wheels] #5443582 05/31/20 09:52 PM
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wings&wheels Offline OP
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Thanks all.

We'll take a look at the generator circuit, I like the idea of a parallel wire.


'05 Lotus Elise S/C
'85 Land Rover 90 diesel
'74 Triumph TR6
'74 BMW 2002
'72 Land Rover Series III 88"
'99 Porsche 996
'01 Porsche Boxster S (mostly Wife's...)
'19 VW Golf R (Wife's)
Piper Pa28-236


Re: Can a car have too much battery? [Re: wings&wheels] #5443623 05/31/20 11:43 PM
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It could be overkill in a way... if the car is low use, and the battery has intrinsic self discharge, and now the generator has to make up for more battery charging of larger capacity batteries, for longer times... yes, it can add wear and tear.

Whether that’s an issue here is a question only the owner can say.

Two large parallel batteries can source more fault current. So my greater concern would be the weak links in older wiring which could start on fire in case of a short in the right spot...

Re: Can a car have too much battery? [Re: spackard] #5443664 06/01/20 06:07 AM
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Originally Posted by spackard
I had a '61 Buick with a generator. I wasn't very impressed with the size of the power wire connecting the generator output to the battery.
I think it was 6 feet of 10ga or 12ga; seemed small by today's standards.
I put a parallel 10ga conductor in, to lower resistance.

In 1961 that generator was what, 30A? 40A? Maybe not even that much.

I wonder if that wire size was selected as part of the system, chosen deliberately for its loss. Kinda like how they used to use resisitive wiring for the coil, so as to drop 12V down to 6V for the points, when 12V systems came along. Wild guess on my part though--I probably would have thought to make the wire thicker too, given half the chance.


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Re: Can a car have too much battery? [Re: wings&wheels] #5443686 06/01/20 07:17 AM
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In the example of a discharged battery bank with greater than designed capacity, my (purely speculative) concern would be toward the duty cycle of the alternator at full load. Was the alternator engineered to avoid overheating and associated issues with bushings/bearings/shafts/etc. while generating its maximum output for an extended period of time?


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Re: Can a car have too much battery? [Re: wings&wheels] #5443696 06/01/20 07:45 AM
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Originally Posted by wings&wheels
Thanks both. That is my thinking.

If the batteries were severely discharged, the generator would charge and supply the vehicle at its maximum until the batteries were at their normal state. Maybe it would run at that higher output longer (than with the small originals), but would operate normally.


Let me define this a bit further as there is a lot of incorrect and misleading information posted to clear it up.

Assuming a properly built generator ( alternator) with regulator etc. and rated for the specific application. ( that qualifier has to be there)

There is no such thing as a generator overloading (defined as the generator internally overproduces)- what happens is the regulator senses low voltage and usually speeds up the prime mover ( exceeding the RPM of the generator causing field issues or magnet issues). This can and often does happen in a Pgen set unless proper controls are in place. It would be more correct to say its being "over driven". ( this is excluding shorts and failed components telling the generator isn't meeting demand because that's not a true overload in the sense)

On a car however, this isn't going to happen without taching out the engine ( if that happens the battery isn't going to be the big issue)

So on a 6-12 VDC system where a functioning regulator senses voltage lower than the cut off- the generator will rotate and excited and charge at the rate until properly relieved. It wont hurt or overstress anything because that's that the generator is designed to do.

The regulator will adjust charge rate based on load requirement as the demand fluctuates

So if there was a chronic dead battery and the road trip was from Texas to the planet Jupiter, there may eventually be service factor issue or component fatigue but not significantly different than normal system entropy.

Hope that helps

Last edited by ABN_CBT_ENGR; 06/01/20 07:48 AM. Reason: clarify
Re: Can a car have too much battery? [Re: wings&wheels] #5443699 06/01/20 07:47 AM
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A generator DOES NOT have a current limit. Cycling on the over current relay contacts in the regulator will burn them out quickly. You can easily burn up the armature, this is something that these days s very expensive if you can still get them.

The old time voltage limit is too low for modern batteries, the regulator needs adjusted to 14.2 at a minimum, 14.5 if you do not drive much. You must know how, do not just go in there and move/bend contacts. You bend spring seat to increase/decrease tension as needed. Many new regulators are VERY poor quality. Make sure the reverse current relay is working, otherwise you can flame the generator, and maybe even burn up the car.

Do not put in large amp hour batteries.

Rod

Re: Can a car have too much battery? [Re: ragtoplvr] #5443701 06/01/20 07:51 AM
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Originally Posted by ragtoplvr
A generator DOES NOT have a current limit. Cycling on the over current relay contacts in the regulator will burn them out quickly. You can easily burn up the armature, this is something that these days s very expensive if you can still get them.

The old time voltage limit is too low for modern batteries, the regulator needs adjusted to 14.2 at a minimum, 14.5 if you do not drive much. You must know how, do not just go in there and move/bend contacts. You bend spring seat to increase/decrease tension as needed. Many new regulators are VERY poor quality. Make sure the reverse current relay is working, otherwise you can flame the generator, and maybe even burn up the car.

Do not put in large amp hour batteries.

Rod


We used to bump them to 120VAC on alternators and make mini camping generators out of them long before inverters hit the scene ( works good for a while)

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