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Best practices for battery wiring on a duel battery system with PDM

PDM Installation & Configuration

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I realize I could have posted this in basic wiring but since this car is using a PDM and has a few accessories not typically associated with race cars I figure I would asked here.

The setup: 1984 Jeep CJ7 limited restomod built and border inline 6 and kenne bell 2.2 super charger MPFI intake conversion running of a Holley HP ECU and an HP eletronik PDM, two optima yellow top D34/ 78 batterys, 2 class D car audio amplifiers ( helix and focal ) and a winch.

The question: how to charge both batteries from the alternator?

In this setup the Holley HP ECU requires a connection directly to the battery (+ and - not just +) the side terminals on these batteries provide a good dedicated noise free connection. I'm running a 12 volt system with additional capacity for the amplifiers and winch not a 24 volt system because one of the amplifiers will not run on 24 volts ( Focal FPX 5.1200)

What's the best practice on this ?

My plan is to run the ECU and PDM from one battery ( in this case top battery ) and run the amplifiers and winch from the second battery this way if someone leaves the stereo on for too long with the vehicle not running you still have a vehicle to drive and are not stranded in the middle of nowhere. This setup because of the PDM would end up running the majority of all powered devices with the exception of the stereo and winch off of one battery.

Alternative setup would be to have these running together in 12 volt configuration with twice the capacity, which is great untill it's not when one battery goes dead and it kills the other one.

These batteries are both 4 post batteries and provide an additional option for running something like the PDM to the other side post if they are wired together. ( Or have to be wired together since alternator wiring will effectively do that )

Let me know what you think the best practice is for this setup.

Thank you !

Attached Files

Off the top of my head, I don't see how you would keep the batteries totally separate systems, while also charging both with a single alternator at the same time.

I'd wire the batteries in parallel. While yes it's possible one battery could in time develop an issue before the other, many trucks come this way and it works well. I do replace both batteries when one eventually has an issue, as the other would likely follow since they've led similar lives.

A dual alternator setup would be a more involved option.

In terms of the concern about draining the batteries while listening to the stereo at engine off, a low voltage warning light to alert occupants would be a very cheap option that your PDM could control.

There are specialist alternators with two separate charging circuits, (12+12V, 12+24V, 24+24V) but easiest and cheapest would be to get a simple splitter, which is little more thn a dual, high current, diode pack or something more advanced, like these https://webshop.vetus.com/en/products/electricity-on-board/battery-splitters

Any boat or camping equipment dealer should carry a wide range - just make sure it has a capacity in excess of your alternator's output in case it might overheat (talk to them) and is suitable for the voltage, 12V, you're using. As you can see above, there's also the option of running two alternators into two or three batteries

As an aside, they're also very useful for running a charge to a race-car's battery while it's being trailered, so it's topped up and ready on arrival.

Wow Gord thank you so much that was exactly what I was looking for !!

I'm interested in this version of the idea as it also used MOSFETs and is In a marine friendly ( read Jeep) sealed package. https://www.getlithium.com/29l_Perfect_Switch_Dual_Rectifiers_Gen4-300Amp.html

Any ideas ?

Not super cheap but nothing on this jeep is so not really surprised.

I'm going to call and make sure this will work with the AGM batteries

Ohh I forgot to mention a bunch of MOSFETs in the circuit between the battery and alternator should reduce noise and provide really good power for the amplifiers so it's a win all around

That looks like the business, it also has a high current rating, with higher available if you have a real butty alternator.

The only caveats seem to be they're primarily focussed on Li ion batteries mentioned, if you're considering a dual alternator installation as they don't seem to offer that option, but may just have missed them on their site - they have a LOT of options!

A 'phone call is definitely in order :-), and I must remember them if I ever need a similar setup.

David, thanks for catching my typo.

Gord that's neat. I'd not heard of this before. Thank you for sharing.

Just for anyone that finds this later a would like more info, I was told they would be perfect for my AGM yellow top batteries and the actual manufacturer is perfect switch in San Diego California. Also worth mentioning there is one connector on there for remote monitoring and activating the bridge mode ( combined cranking amps ) that is not 100 waterproof but some how brew potting can take care of that. ( If your application is a boat or a 4x4 where somebody might get over zealous with a pressure washer this might matter )

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