Questions on dual battery + dual alternator (1 Viewer)

[lovetoski]

I'm getting parts and info organized to do a desmog on my 60 soon. One option for my smog pump is a second alternator. I already have an extra 55am alt, so that's paid for. I already have a dual battery system, so the obvious way to do this would be similar to how godwin and kevin did theirs...one alt per battery.

https://forum.ih8mud.com/60-series-wagons/94294-fj60-dual-alternator.html

https://forum.ih8mud.com/60-series-wagons/222516-130-150-extra-amps-2f.html

I am currently using a VSR (voltage sensing relay) to charge the second battery. System works fine for 4+ years.

My question is about combining batteries when using dual alternators...Can you combine the batteries with dual alternators (eg for winching)? What I'm not clear on is whether two alternators "fight" each other when they're linked up?

I already anticipate using a switch to choose which battery to run the truck from...so I can isolate one as the starting battery while using the other for in-camp use.

If I can combine them, then my plan is to delete the VSR and instead use one of these marine switches to switch between or combine the batteries when/if I want.



Any advice is much appreciated!

Thankyou!

 

[StevoJonesFJ60]

Sounds like a good plan, I would look into optional uses for the second alternator.
There are some good write-ups in the tech section about using an alternator as an on board welding system. Although I don't think the 55amp alternator would be powerful enough.

In regards to "combining" the batteries the only way that would work would be if you wired them in series. In theory you might be able to use the switch idea to do this.
One setting for Bat A, one for Bat B, one for A+B, and one for no batteries(A little theft prevention measure) Not sure if this is practical/possible in reality though.

 

[lovetoski]

Here is a simplfied wiring diagram of what I "think" I want to do. Most grounds are not shown. Wires thickness not representive of guage. The combiner switch is the one shown in the first post. Will this work? I'd like be able to choose whether batt 1, batt 2 or both would send electricy to the various loads. This would need to work regardless of whether the truck was off, or running (running means both alts would be producing amperage).

 

[StevoJonesFJ60]

The way you have that set up there is no provision for 24V operation, you would need to do something like this.

 

[StevoJonesFJ60]

That way you could run off of battery A, B, or Both.

 

[lovetoski]

Stevo,

I am confused. I understand the additional red lines, and how that puts the batteries into series which creates 24V output. However, my truck has 12V electrical, so 24V would fry a bunch of things? Or, I'm misunderstanding something...

Sorry if I'm being a little dense.

 

[StevoJonesFJ60]

Yeah It would probably mess some things up, I don't know for sure though.
You had mentioned combining the batteries so I figured that you wanted to run a 24V winch.
The other thing you could do is run the batteries in parallel that way you would have 12V. But have better amp hour rating. I'm not sure if this would cause any problems.
In the end with the switch, if you got a 4 channel, you could have: A, B, A+B, or none.
The diagram would look more like this:

 

[lovetoski]

The other thing you could do is run the batteries in parallel that way you would have 12V. But have better amp hour rating. I'm not sure if this would cause any problems.

Hi Stevo,

Thanks for the quick response! Ya, higher amp hour rating + higher amps from the two alts (for winching) is what appealed to me. Wiring makes sense.

Thankyou.

Best Regards,

 

[StevoJonesFJ60]

No problem, I would just check and make sure there won't be any problems with combining the electrical power from the two systems.
The alternators might make electrical power at different frequencies.

 

[TobyB]

No, the alternators will let whichever one has a higher voltage regulation point do all the work.
The other will loaf, until you get a heavy load.

No real harm in this, I guess.

Thing is, parallelling batteries usually also tends to undercharge one and overcharge the other.
Not much, but enough so that the overcharged one will suffer a somewhat shortened life.

The systems where I've seen dual batteries like this- I'm thinking RV world, here, with house power and
engine power-
usually only combined the batteries when you really needed them- as in, the engine battery died-
and then separated the systems again.
I think that might be your best bet- use one side as a primary engine battery,
use the other as house power (for winching and things)
and then just use the tie when you really need it.

That was my plan, eventually, but I wasn't going to carry the spare alternator....

fwiw,

t

 

[lovetoski]

Thing is, parallelling batteries usually also tends to undercharge one and overcharge the other.
Not much, but enough so that the overcharged one will suffer a somewhat shortened life.t

That makes sense! So I could run it with the two batteries separated most of the time, and just combine them if/when I need the extra amps (winching for example). With two alts, both batteries will be charged all the time. One will be the primary battery which will power all the OEM and accessory loads, the other will be a "backup." This works just like I was hoping. Thanks!