How to wire dual alternators.

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thegawd

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if there are 2 batteries connected in parallel, they will charge each other until they are the same voltage in each battery.

when hooking up batteries together like this for say an off grid solar set up, it's best to get matching batteries that are the same age. I assume the same holds true in a vehicle. this helps avoid that as they charge at the same rate and deplete at the same rate. I have never dealt with a vehicle with 2 batteries though.

Al
 

PlayingWithTBI

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I assume the same holds true in a vehicle. this helps avoid that as they charge at the same rate and deplete at the same rate
^^^Exactly! As an example - at work I had an EZGO golf cart which had 6 - 6 Volt batteries for a 36 Volt system. Our Company policy was we had to have our headlights on all the time, especially when driving inside the plants. The lights were hooked up to 2 batteries to get 12 Volts. The batteries wouldn't last much more than a year even with charging every time we parked them (we had 6 golf carts). When you pay over $100/battery it got pretty expensive. I found a converter which takes 36 Volts and converts it to 12 Volts for about $300 IIRC. After that, the batteries lasted ~3 years because they were being drained and charged at the same rate. :waytogo:

One weak battery will ruin the other good battery because it's getting over charged to maintain the weak one.
 

GoToGuy

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if there are 2 batteries connected in parallel, they will charge each other until they are the same voltage in each battery.

when hooking up batteries together like this for say an off grid solar set up, it's best to get matching batteries that are the same age. I assume the same holds true in a vehicle. this helps avoid that as they charge at the same rate and deplete at the same rate. I have never dealt with a vehicle with 2 batteries though.

Al
Direct Current- How do two batteries in parallel "charge " each other? Vehicles not solar arrays with electronic controls and conditioning.
 

GoToGuy

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Golf cart batteries in series? Then a voltage step down to 12v for headlights. Did you consider led conversion that have wide DC operating range? Or just 12v led headlights? I see where your going. Who ever designed the golf cart lighting took a shortcut knowning they were shorten, the battery life. It's the operating conditions. It's not they were weak. Its that they operated at their limit of ability. So the conditions, powering the incandescent headlamps and on demand power for motor power. The two tapped for 12v would never charge at the same rate. They were basically worked to death.
 

GoToGuy

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Golf cart batteries in series? Then a voltage step down to 12v for headlights. Did you consider led conversion that have wide DC operating range? Or just 12v led headlights? I see where your going. Who ever designed the golf cart lighting took a shortcut knowning they were shorten, the battery life. It's the operating conditions. It's not they were weak. Its that they operated at their limit of ability. So the conditions, powering the incandescent headlamps and on demand power for motor power, they allways had a higher demand placed on them. The two tapped for 12v would never charge at the same rate. They were basically worked to death.
 

Nick_R_23

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Direct Current- How do two batteries in parallel "charge " each other? Vehicles not solar arrays with electronic controls and conditioning.

It’s not so much “charging each other”, it’s simply voltage stabilization. The big reason multi-battery setups state that it’s necessary to replace all batteries at the same time and be the same spec, and same manufacturer, is there is a great variation on how batteries are manufactured. The charging system will base its efforts off the weakest battery, so if you have a junk battery in the system, the other batteries will only ever be as good as that one.

Some of the differences and variations in batteries can be the number of internal plates, the quality of materials used to build the battery, varying levels of acidity within the solution which can make a battery more powerful at the expense of service life, plate sulfation (essentially the percentage of the battery that is compromised), dead cells, defects causing internal resistance, and much more.
 

GoToGuy

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When discussing. mulitple batteries, " hooked up" is kinda vague. You doing series or parallel, gives a better minds eye what your describing.
 

Nick_R_23

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I think the parallel part is kind of implied here as these trucks are 12v systems. Not likely anyone is using 24v+ setups.
 

GoToGuy

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It’s not so much “charging each other”, it’s simply voltage stabilization. The big reason multi-battery setups state that it’s necessary to replace all batteries at the same time and be the same spec, and same manufacturer, is there is a great variation on how batteries are manufactured. The charging system will base its efforts off the weakest battery, so if you have a junk battery in the system, the other batteries will only ever be as good as that one.

Some of the differences and variations in batteries can be the number of internal plates, the quality of materials used to build the battery, varying levels of acidity within the solution which can make a battery more powerful at the expense of service life, plate sulfation (essentially the percentage of the battery that is compromised), dead cells, defects causing internal resistance, and much more.
So the charge each other was a little fib. Example- my Duramax battery is not carrying load anymore. Repair is 2 new high quality batteries correct group size and amperage rating of at least what GM requires. Same size, same cca. Connected in parallel. Are you talking about multi battery power banks, backup power supply or dual battery trucks and dual alternators? " charging system will be based on weakest therefore thats your power level" ? Didn't you just say the charging system will keep trying to chargethe weaker battery resulting overcharging good batteries?
 

GoToGuy

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I think the parallel part is kind of implied here as these trucks are 12v systems. Not likely anyone is using 24v+ setups.
The reference was to just be clear. All GM Military operate on 24v systems. When starting relays shift battery power to 12v parallel for starter.
 
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