# Using multiple alternators at once for a power source

Iga
TL;DR Summary
How to connect multiple alternators and create power bank
Hi

I need to create a electricity generator, I've got plenty of car alternators and car batteries, all are 12v. I know how connecting batteries in parallel / series, basically i could connect like 20 car batteries to have a 12v massive amperage power bank which would cause an issue with wire thickness at some point or make it parallel /series to get 24v or 48v or even 120v, this having lower amperage and so thinner wires. The question is how to connect all these alternators since if i connected them in parallel it would give me max of 2000a at 12v(or more, i know they charge closer to 14v)but would that cause any issues? Or can i connect them in series to get 120v at lower amperage? They have all those regulators and are different sizes but all are 12v.

## Answers and Replies

Mentor
Welcome to the PF.
I've got plenty of car alternators and car batteries, all are 12v. I know how connecting batteries in parallel / series, basically i could connect like 20 car batteries to have a 12v massive amperage power bank
It is a very bad idea to connect non-matched batteries in parallel. Parallel car batteries are usually the same age with the same charging history. If they are not the same age with the same charging history, you can get significant currents flowing between them when they are connected in parallel.

Iga
Thank You berkeman, I'm trying to understand it all as i have to create this small power plant soon. If so then I'd have to connect them in series yet my understanding of it is that if I'd have let's say 2 12v 100amp batteries it would give me 24v 100amp, yet what would happen if they were eg 12v 100amp and 12v 65amp? Does it have any chance of working and not blowing up?

Mentor
What kind of power plant? What is your source of mechanical energy? How much mechanical power do you have available?
what would happen if they were eg 12v 100amp and 12v 65amp? Does it have any chance of working and not blowing up?
That's too mismatched to be useful. They need to be the same type and capacity, with the same charging history. You could potentially parallel same-voltage batteries if you diode-OR them, but then you are losing efficiency in the connection diodes...

Iga
I definitely should clarify whole situation. So i got a bit of land and i have to move there before the end of February, got all other things, nice mobile home etc. Now the power plant is supposed to basically run entire house since connecting to the grid at that location would cost 10s of thousands due to distance.

I've already made entire drive system, source of energy is old diesel engine, I got one big pulley on the engine giving 4/1 ratio on the alternators, I've already made entire drive system so that engine at 1500rpm spins them at ~6000 rpm, I've connected all remotes (unless it's called differently) to switch them on like when car ignition "activates" the alternator. I know there might be some belt slip etc. Theoretically this engine has around 80hp or ~60kw at 1500rpm and off these alternators can in theory put out from 90 to 150amps each at really something like 14v that would be plenty of power since let's say on total that have max theoretical power of 1300amps at 12-14v

I need to make this system run temporarily and with time i could get some different batteries, possibly add wind turbines and solar panels but at the minute i don't have funds for it.
I know that car batteries, if drained too much, will have much shorter life but they're going to scrap anyway as I've nothing else i can do with them even though they're still good so i don't mind having to change them to some proper power bank in few months.

Important note too, i use a lot of electricity, 2 boilers, pumps, pc, welder, tv screens, audio system, fridge, oven, kettle, my work lights at home are like 600v and i usually use 2 or 3 of them at once.

Staff Emeritus
https://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations

Battery University is a very good source for all battery-related information.

That article says the same as @berkeman said, it is OK to parallel batteries as long as they have the same brand, size, type, age, and state of charge. If one goes bad, you need to replace all o them, not just the bad one.

Series-parallel connections are possible. For example 2 x 12V batteries in series to make 24 V, plus a second bank of 2x 12V in series to be paralleled with the first bank.

The article also mentions using fuses and other protective devices to protect unbalanced batteries in parallel.

I have experience with batteries in parallel, but not with alternators in parallel.

Mentor
Connecting alternators in series or parallel may also be fraught with issues. I'm under the impression that alternators do not produce a steady DC output, but rather a rectified AC. I don't see how you could achieve (or maintain) synchronizing every alternator to be have identical phase so that they don't "fight" each other. I suppose using a voltage regulator and battery to smooth each output could work. Basically duplicate a car's charging system for each alternator.

Gold Member
How about connecting the alternators one to each battery with isolation diodes as @berkeman suggested? Since the frame of an alternator is the Ground (negative lead), the mounting system will have to isolate the alternator frames from each other. But you would have to isolate them anyway if you series-connect them.

If you choose another approach, I would not expect any problem connecting the alternators together in either series or parallel. They ar 3-phase devices and have a full-wave bridge rectifier in them. That means their output ripple voltage is only 4.2%, not enough to worry about.

If the alternators are connected in series, without diodes for battery isolation, remember that the current will not exceed the lowest rated alternator in the string.

It's the batteries that have to be handled with kid gloves!

Also, I just checked availability of inverters. Here in the USA a 2kW is USD$165 and 750W is USD$65. So you could have several individual alternator-battery-inverter systems each supplying separate circuits.

And of course lower power lighting circuits can be 12V, even small refrigerators are available for 12V operation (used in campers/RVs (Recreational Vehicles)).

Cheers,
Tom

berkeman and anorlunda
I definitely should clarify whole situation.
...
Given the described situation I would suggest you to revise your plans. DC current at this level is just too inconvenient. Battery based UPS systems rather opt for higher (48 or higher) voltage than this caliber of current: but at higher voltage you need appropriate batteries and connecting the alternators in series is also a very difficult thing if you want to use it for charging.

I would just look for a diesel (?) based generator directly at the desired line voltage instead. You will make your life very difficult with the described kind of DIY kludge.

Tom.G, jrmichler, berkeman and 1 other person
Dullard
I 'shocked' that this thread hasn't been locked, but:
Many (most?) alternators are chassis-grounded. They should be used in series only with great caution.

sandy stone
Iga
Thank You for all the information, i guess going with separate alternator - battery - inverter would be the best, i can actually get 500w converters for like €20 each, those are "car coverters" to be used with cigarette lighter in a car.

The last question is if i can just connect wires from converter outlets if there's going to be like 10 of them or are there any issues with that?

For all the other things this is the way to go for me for many reasons starting from money going to the fact that is rather learn how to do things and do them myself instead of paying others to maybe do them right... I guess I'm a rebel of sort.

Dullard
If you're talking about 'ganging them up,' then yes - there's a problem. The individual converters will not be 'in-phase' - connecting the outputs will be a disaster. I don't want you to take this the wrong way:

STOP! You don't have the minimum required knowledge to proceed. You can certainly acquire that knowledge, but as it stands, you're going to kill yourself or damage property before you realize what you don't know. In this particular case, you need some 'theoretical' knowledge before attempting to educate yourself empirically.

Staff Emeritus
Ay ay ay. The experts (meaning me ) completely missed the serious safety problems with running chassis grounded alternators in series. @Dullard is right. Apologies.

Thread closed because of dangerous topic.

Last edited:
OCR
Thread closed because of dangerous topic.

Need a bit of help ? 😒

.

berkeman