Advice on charging (2) 81ah FLA dump trailer batteries

[dudedogvan]

I run a tree service and recently bought a F350 flatbed dually truck to tow a 20' dump trailer for hauling tree debris. The hydraulic dump is powered by (2) 81ah FLA 12v batteries wired in parallel. It came with a measly 5A AC charger I can plug into a 110v extension cord, but I'd rather charge the batteries on the go with the truck's alternators. The truck is heavy duty, so it has (2) FLA batteries under the hood and (2) alternators: primary=175A, secondary=157A.
From what I found so far, using the 12v accessory pin on the 7pin trailer lights plug will be insufficient as there will be too much voltage drop. Solar might be an option, but I'd rather charge it with the alternators because I'm concerned the panel could get broken with the tree work.
That leaves 2 viable options I have found:
1) DC-DC charger (probably a REDARC unit)
2) Anderson PowerPole plugs on large gauge wire Setup (possibly involving an isolator), this is the more economical option

How many Amp charger for DC-DC would you recommend? REDARC makes a 12A, it's cheapest, will that suffice?
Can I use the 12v accessory pin on the 7pin connection even though the wire is smaller gauge because the DC-DC charger will adjust the voltage? Or will I need to use Anderson plugs anyways so I can incorporate a larger gauge wire from the truck's battery?

If I just use Anderson plugs with sufficient gauge wire, do I need an isolator?
Do the alternators work at the same time or how does that work?
Will the alternators be able to support charging a total of (4) FLA batteries and keep them all topped off?
From what I understand, with this method I'll be wiring the 2 trailer batteries in parallel with the 2 truck batteries through an Anderson plug and adding a breaker on the trailer side, that's all. Does this wiring present problems I'm not considering or is it safe and effective?
Here's a link to a company that supplies Anderson plugs wire kit that seemingly solves this problem for dump trailer owners, no isolator, spoke with owner and said no isolator needed.
PolePalUSA Kit

Thank you for any input!

 

[dudedogvan]

nobody?

 

[Vigo]

How many Amp charger for DC-DC would you recommend? REDARC makes a 12A, it's cheapest, will that suffice?

Can I use the 12v accessory pin on the 7pin connection even though the wire is smaller gauge because the DC-DC charger will adjust the voltage?

Should work because even if there is serious voltage drop going on it shouldn't pull more than ~16-18 amps on that circuit. The 7 pin connector is rated at ~30a for that terminal i think, but the actual wiring on the truck may not support 30a. 16-18a is a reasonably safe assumption but it is still an assumption.

Or will I need to use Anderson plugs anyways so I can incorporate a larger gauge wire from the truck's battery?

If the circuit feeding the 12v pin on your 7pin connector can't handle even the ~16-18amps then you would have to upgrade that wiring to feed the DC-DC off of that, or you could skip the DC-DC and the wiring upgrade it MIGHT require, and just do a big wire to anderson connector like you were saying.

If I just use Anderson plugs with sufficient gauge wire, do I need an isolator?

Not really. A voltage sensing relay is <$20 on amazon so not a big expense to add one, but it doesn't protect against much of anything in this situation.

Do the alternators work at the same time or how does that work?

I haven't specifically looked it up but im guessing for heat management reasons the two alternators are more or less in sync in terms of how much current they provide. So they're both 'always on' and split the load, is my assumpton.

Will the alternators be able to support charging a total of (4) FLA batteries and keep them all topped off?

Definitely!

From what I understand, with this method I'll be wiring the 2 trailer batteries in parallel with the 2 truck batteries through an Anderson plug and adding a breaker on the trailer side, that's all. Does this wiring present problems I'm not considering or is it safe and effective?

Well, i would definitely add a fuse or breaker near the front of the truck.. Only the wire downstream of the fuse/breaker is protected, so you generally try to make the upstream as short as possible and put the fuse/breaker as close to the power source as possible.


Also, just to point out, you don't have to run a ground wire the full length of your truck. It is chassis ground so you just need a long POWER wire, but the ground wire you can simply go from the anderson connector (on rear bumper?) over to the frame rail.

If you don't already have the DC-DC i would just buy the wire and anderson plugs, personally. The DC-DC idea is more 'elegant' but probably overall about 2-3x the cost.

 

[dudedogvan]

So I'm reading: just go with Anderson plugs and an appropriate breaker.

That kit I linked comes with 2awg wire and a 300A breaker. It also already includes full lengths of both positive and negative wire running the full length of the truck, so your idea with the negative wire is great, but for the price the kit is worth it. Then I won't have to assemble anything. Plus I'm not sure where you're saying the negative goes to be honest. I'd probably need to see a simple diagram to grasp it. I've only ever done a 1 simple solar setup in a van, so my power knowledge is minimal.