Dual batteries

marty79

marty79

Well-Known Member
Joined
Nov 24, 2013
Location
Newton, NC
What's this about having to run an isolator which are pricey. I have a second battery and ready to put in but now I've read too much on insulators and these fancy mumble jumble kitsch that I'm confused lol.
Can you not just wire 2 batteries in sync? Do I need a switch? Isolator thing?
 
Diesel trucks all have 2 batteries, no isolator. The purpose of this is to provide higher cranking amperage.

Dual batteries in high accessory load applications are for increased reserve capacity. This is where you will find isolated systems. If you kill one battery it won't take the other one with it.

Why do you want two batteries?
 
Falko said:
Why do you want two batteries?
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This is the key question to determine the answer.


To spell it out a little better.
If you have two batteries wired in parallel (Just fyi there is no "sync" - that is relevant to AC systems where you synchronize the wave forms, DC doesnt have a wave since its direct not alternating) and one battery fails and has a bad cell or internal short, that battery will kill the other battery. And possibly create sucha shock load (electrically) that it ruins the other battery. An isolator can prevent this.

Also on some offroad rigs a separate battery will be ran dedicated to the winch to prevent voltage sag from potentially damaging the ECM or causing undesired performance issues while winching. In this scenario that battery is (usually) totally isolated except for a tie to the alternator to charge it. You would need a small isolator (or diode) to prevent that battery leaching back into the system through the alternator.

Or a couple other scenarios I can conjure up like 24vdc starting and 12vdc accesories or or or..

So back to the beginning, why do you want two batteries?
 
Falko said:
Why do you want two batteries?
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For using the winch, I could've bought bigger battery but since I have 2 why not combine them for when pinching, and I suppose my dual electric fans do draw a lot so that's my reason. Thank you
 
If you want to put them in parallel with no isolator, go buy a new pair of identical batteries and permanently wire them in parallel (like a truck).

If this does not align with your plan, you should probably rethink your plan. Really just depends on how risk adverse you want to be.


There are many cases where "I don't want to do it right, I want to do it cheap" is not a great plan.
 
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Fabrik8 said:
If you want to put them in parallel with no isolator, go buy a new pair of identical batteries and permanently wire them in parallel (like a truck).

If this does not align with your plan, you should probably rethink your plan. Really just depends on how risk adverse you want to be.


There are many cases where "I don't want to do it right, I want to do it cheap" is not a great plan.
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History suggest he will hear a bunch of good advice and then do whatever is the opposite of said advice.
 
Jody Treadway said:
Y'all overthinking this, like always.
Turn one battery upside down, touch the + to +, - to -, ratchet strap with a quality one from RK and rock out.
Cut hole in hood for top floor battery clearance.
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How do you expect to keep all the lectricity from leaking out this way?
 
Just wire it like this. When you start with 24v it takes twice as long to drain it down to 12v.

24v a.jpg
 
Fabrik8 said:
If you want to put them in parallel with no isolator, go buy a new pair of identical batteries and permanently wire them in parallel (like a truck).
Click to expand...
Ok so that's what I wasnt unsure of..both batteries have to be the same which mine aren't so I guess you're saying i will need one of those switch things to switch it on/off? Is there still a way to use both batteries when winching or is that only if they're same size. Thank you
 
jeepinmatt said:
History suggest he will hear a bunch of good advice and then do whatever is the opposite of said advice.
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with fab work on my rig yes, but stuff like this nope.
 
marty79 said:
For using the winch, I could've bought bigger battery but since I have 2 why not combine them for when pinching, and I suppose my dual electric fans do draw a lot so that's my reason. Thank you
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Regarding your dual fans, are they controlled by a relay or are they straight wired? Because that will have a profound impact on your battery performance under load
 
marty79 said:
Ok so that's what I wasnt unsure of..both batteries have to be the same which mine aren't so I guess you're saying i will need one of those switch things to switch it on/off? Is there still a way to use both batteries when winching or is that only if they're same size. Thank you
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You don't need 2 batteries for a winch and 2 fans :rolleyes:
 
@marty79 if you need/want a great relay for your dual fans, the Napa ST85 solenoid style is a great choice.
I'm assuming you're having issues while winching with the fans on. If so and you don't have a heavy duty relay, that can happen. Also, ground the piss out of the chassis, engine and winch.
Food for thought.
 
Jody Treadway said:
@marty79 if you need/want a great relay for your dual fans, the Napa ST85 solenoid style is a great choice.
I'm assuming you're having issues while winching with the fans on. If so and you don't have a heavy duty relay, that can happen. Also, ground the piss out of the chassis, engine and winch.
Food for thought.
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it has a relay...weather it's HD or not I don't know. ALternator is perfect working order, I actually just did a refurbish cleaning on it so it's stock 130amp unit btw.
I'm not sure about the relay, it's got pretty thick wires coming out of the relay if that says anything and their Taurus fans.
I also should add I haven't used the winch since I did the refurbish job on the alternator, had it tested and tested perfect at 126 amps. Before this, yes running the fans and the winch it would actually stop the winch but I'm not sure now. I just figured it was "good idea" to put in another battery and share the load when winching?? maybe? I admit I'd rather not buy another bigger battery, the one I have is 625 CCA and practically new, the other battery is Interstate 680CCA (I believe) but I've already relocated my primary battery with new made box for the current Duralast Gold 625CCA battery I'm running. This other Interstate I just acquired not long ago for well, free lol and it's in good shape.
 
Jody Treadway said:
Napa ST85 solenoid
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i see this is like a starter solenoid? and you're saying to use this for the fans? this is all new to me, seems beefy. I've never seen anything like this for fans wiring...
 
marty79 said:
it has a relay...weather it's HD or not I don't know. ALternator is perfect working order, I actually just did a refurbish cleaning on it so it's stock 130amp unit btw.
I'm not sure about the relay, it's got pretty thick wires coming out of the relay if that says anything and their Taurus fans.
I also should add I haven't used the winch since I did the refurbish job on the alternator, had it tested and tested perfect at 126 amps. Before this, yes running the fans and the winch it would actually stop the winch but I'm not sure now. I just figured it was "good idea" to put in another battery and share the load when winching?? maybe? I admit I'd rather not buy another bigger battery, the one I have is 625 CCA and practically new, the other battery is Interstate 680CCA (I believe) but I've already relocated my primary battery with new made box for the current Duralast Gold 625CCA battery I'm running. This other Interstate I just acquired not long ago for well, free lol and it's in good shape.
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You have dual Taurus fans? WTH for? Those things spike over 100 amps on start up.
My 11:1 400+ HP stroker with a stock 3.0 V6 radiator stays cool with a single one.
 
Jody Treadway said:
You have dual Taurus fans? WTH for? Those things spike over 100 amps on start up.
My 11:1 400+ HP stroker with a stock 3.0 V6 radiator stays cool with a single one.
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I know of a crate 502 with a silly small 24x 19 or something radiator, with a Taurus fan and it keeps it cool.

We control it with the autometer pro something gauges. The gauge can be set to trigger relays for hi/low speed fan operation.

We have a normal 40a relay for low speed, and use another 40a relay to trigger the st85 relay(solenoid) to power the high speed.

The gauge triggers the relays on the ground side, so high speed required the use of two relays due to the amperage required to energize the coil on the solenoid. Also makes the low speed relay shut off when the high speed cuts on, so that both aren’t energized at same time.

I can get picture tomorrow.
 
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