Advice on house to vehicle charging

[Vicad88]

Hello,

I have a 24v system in my boxtruck conversion with 3080w of panels. The vehicle also has 3 standard lead acid batteries for starting the engine.

I replaced the LAs a few months ago, and I noticed that both the positive and negative are attached to the first battery, and they are chained from there. I wasn't able to fix it at the time, and I admittedly should have addressed it before now, but here we are.

My root issue is the vehicle batteries are slow draining to the point it won't start without a jump. I also have a camera system that I would like to leave running, which will further tax the batteries a bit.

My first question is: What would be the best way to extend the length on the battery cable from the vehicle so I can get them connected on opposite ends of the set? Better to do pos or neg or does it matter? Assume I won't be able to pull a new wire.

My other questions: I would like to add a charge line from my setup in the house to the vehicle batteries. It would not need to be much/fast, just enough to keep them topped off. I assume I would need some sort of isolator to prevent it from trying to draw from the house batteries and burning out the wire/popping the fuse? I am using a Victron Orion 24 to 12 70amp for my 12v stuff. Could I run the line off of that at the blade fuse block? This will be about a 30ft run for sizing.

Thanks for your help in advance!

 

[justinm001]

Do you have a shunt? If not just put the shunt on the neg cable then add a 2nd cable from the last battery to it. If already a shunt then a on/off battery switch to the pos. Easiest way to extend.

Is the start 12v or 24v? Typically you want to isolate the start from house systems. Eliminating any parasitic drains on the starter.

To charge either or both just get a basic 120v to 12 or 24v charger. They make 20/10 amp 12/24 ones all over Amazon I have a few in my rig. Get 2 of them one for house and other for start then connect together with a power strip then plug into house. Problem solved both banks will slowly charge.

 

[Vicad88]

Sorry, I forgot to mention the start batteries are regular 12v.

 

[0truck0]

You might have all the info here, but is just too much to try to get details sorted out for a quick read and response....
We are talking about both starting vehicle batteries and RV batteries?
The 3 starting batteries are 12v?
The RV battery(s) are 24 volt?

Do you have the 12v and 24v system connected together? If so, is it connected only when alternator is charging or all the time?... diode? switch? other?
For starter batteies, yes connect opposite, and I would assume you would want to mess with the neg cable (extend the neg not the pos). Connect positive on battery 1 and neg on battery 3 so the current passes through all 3 batts equally. As-is you are drawing most from batt 1, some from batt2 and the least from batt3. This same thinking applies to charging and discharging the same.

Technically you want the pos and neg cables to be the same length for charging.

Connect the charger to the starter batterie's unused post just for clean and simple. So, neg to the first and pos to the 3rd battery (and pos to first and neg to last for the starter/vehicle use). or really just whatever works for you.

The two sets of batts should not be electrically connected when the RV batts are not being charged by alternator. Use diode or relay switch or some device that disconnects them.

You need to first address why the starter batts are slowly draining. I would guess it has to do with your connection to RV batts. It must be set up wrong.

 

[Vicad88]

Thanks for your reply,

You are correct, the starting batteries are 12v and the RV batteries are 24v. I am using the victron 24v to 12v converter for my 12v needs in the rv that I could tie in to.

The starter bats are not currently connected to the rv system. The phantom draw could be from any number of things up in the cab, I will look in to that at another time. It's possible the batteries being not connected properly at 1 and 3 is causing the alternator to not charge them well enough which is contributing to the problem.

You suggested extending the neg, is there a best way to do this? I have extra lugs and cable from building the rv system. Would building a cable with lugs and using a bolt to connect the lugs together at the extension be sufficient?

You mentioned a diode or relay or some sort of device... this is where I'm most unfamiliar. The idea I have in my head would be running a wire from the 12v portion of the rv system to the starting batteries. I think a trickle charge would be fine, so I don't think a DC-DC charger would be nessesary. I do think I need some sort of device to separate them once the vehicle starts, to prevent it from trying to draw from the rv system on start or the alternator from sending power back up the line. But what that device 'is' I don't really know.

Any ideas are appreciated!

 

[0truck0]

So, there are two separate questions here.

On the starting batteries, yes, the way they are connected means the third battery might not get charged fully like the first one in the series. The more dead battery (3rd one) will drain the better battery (1st) until all 3 are at the same voltage. This is most likely the phantom draw that is draining all down. The easy fix is to wire as mentioned, then charge all 3 fully (long drive or overnight on a charger).

Many ways to extend the neg cable. Pic of what you have will help for a starting point. Where is the neg connected, to the frame, the block?
You might just need go to auto parts store and buy a longer neg cable, or make a longer one from auto parts store neg post clamp that can be attached to a cable.



To connect RV batts and car batts you can use a "solenoid" This is very common and the auto parts guy can help with this, if not, find another parts store bc this is basic stuff for auto guys. The solenoid connects or disconnects electrical circuit between the batteries. It connects when you send a little 12v power to it, and disconnects when no current present. You use a small switch like a toggle switch or any switch to turn the solenoid on or off. DO internet search and find a million pages on this topic. OR instead of a switch you just pull 12v of the fuse panel / ignition (like the radio power) and send that to the solenoid, so when car is on the solenoid is on, but off when cranking, and this is how I did it, as do most. Key word to know: "fuse tap".
On the pic above, the left and middle solenoid... the little gray metal studs are the 12v+ and 12v- to turn solenoid on. The copper studs are 12v+ in and 12v+ out, which are on/off depending if voltage is applied to the little stud. There is no 12v negative on the big studs.
The solenoid on the right has one small gray stud for 12v+ and relies on the bracket to be grounded to the frame for the 12v-.



You can also use a big "diode". These only allow current to flow in one direction (from car battery to RV battery) and not the other (from RV batt back to car battery). Diodes have a slight voltage loss so not efficient like a solenoid. Diode will not all you to take power from RV bat and give it to the car batt, so you wont be jumping the starter off of the RV batts. Diode should have an on/off function so when car is off the diode is off and no power flows from car batt to rv batt.
Actually the way diode works is the alternator feeds the diode then branches out to rv and car batts, so both batts lose voltage and both batts will have a longer cable feeding them. I think when I had one I only had the rv connected to it and left the car batt alone. I connected to the starter motor positive because that was the closest 12v+ I could pull from.
I would not recommend doing a diode.

There are also specific RV components that do the same thing the solenoid or diode do and might be easier to set up.

With any of the above you will benefit from a DC to DC charger unless you are going from lead acid to lead acid or unless both LA batt banks are close together. With box truck you batts might be all close together, IDK. DC to DC still beneficial with LA long runs, but is really only needed when you have lead acid on car and lithium on RV as these are two different battery types, distance apart irrelevant.

RV forums will be a better source for info than a solar forum as you are not discussing solar panels.

A trickle charger can be added to any battery no matter what set-up you have, just add it to the battery you want to charge, not to the other devices.