solar/battery/cable question

i've realized my current solar set up is not correct. I replaced the PV panels, charge controller, but not the batteries until now.

For my new setup, I have Two 125ah AGM Vmax Batteries. previous owner welded under carriage battery trays, (p cool) one on the passenger side, and another on the driver side. I can only fit one Vmax battery in each compartment. This leads to cable length problems.

I will be wiring the two batteries in parallel, with 0 guage copper wire. These can be equal length. And will probably be somewhere around 60-70 inches (width of van underneath. Obviously the shorter the better, but we don't have a choice here.

I now understand that my cable/wire from my MPPT charge controller, to my batteries can not be going to one battery. one (lets say Positive(+) cable needs to go to the + terminal of one battery, and the Negative (-) needs to reach the other battery's negative terminal across the other side of the van.
My understanding of this is that this length cable can be quite long and is not a concern. I also understand they can be different lengths. (for instance, the + cable from MPPT to battery would be roughly 3-4 feet, but the negative length to the other side of the van will be closer to 10 feet. Is this correct?

Now for the most important set of questions. I believe I should also wire the 0AWG cables connecting the battery bank to my inverter in the same fashion. One cable from one battery, and the other cable from the 2nd battery across.

Can these large cables, from the battery bank, to the inverter be different lengths? If not, would the best option to make both the same, and map them out underneath to "take up length? It would save me a lot of work and time if they can be different lengths. Like in the above scenario, positive cable would be 5ft or less, negative will be closer to 15. Can they also be of substantial length? Im not quite understanding voltage drop yet.


I'm trying to make my batteries as equalized as possible as they charge or as they have a load on them. Or do i simply buy a battery equalizer?

thanks for the help
 

marklg

Well-known member
Matched lengths are not as important on the MPPT charge controller because the current is not that high. The wires to the inverter should be as big as you can make them and matched as possible. This site shows some ways to match the lengths:


Perfectly matched is best, with the junction for - at one battery and + at the other, but in my case it was not possible. I have 1/0 from each battery to a common junction and then 4/0 to the inverter. That is the best I could do, as I have four batteries scattered in different battery wells, some farther from the inverter than others. I would probably not add extra wire just to match the lengths. Shorter and fatter wiring is still better.

I have the advantage of bluetooth monitors in each battery so I can see any mismatch in current and charge. They generally are within a few percent of each other, so I guess my setup is "good enough".

Regards,

Mark
 
ok thanks!

is there a difference to having the + or - battery cable to the inverter being the longer one?

i.e. is there anyy benefit to the negative being longer than the positive, or vice versa?
 

marklg

Well-known member
ok thanks!

is there a difference to having the + or - battery cable to the inverter being the longer one?

i.e. is there anyy benefit to the negative being longer than the positive, or vice versa?
Generally, ground differences cause more issues and confusion, so shorter ground would be preferred.

Regards,

Mark
 
I also just read my MPPT victron charge controller has a battery equalization option in the app settings. Would it be advisable to turn that on once the batteries are correctly hooked up?
 

marklg

Well-known member
I also just read my MPPT victron charge controller has a battery equalization option in the app settings. Would it be advisable to turn that on once the batteries are correctly hooked up?
Look at the battery manufacturer's information and set the controller to whatever they say. Each battery type is different. That is why it is good to have a controller with manually settable voltages and timers. That will make your batteries last longer. I don't know anything about Victron, but my Morningstar has a custom setting. You use a meterbus to USB adapter and a PC and there are dozens of settings.

Regards,

Mark
 
a lil update.

i was able to get my 0/2AWG positve wire to make the connection from my inverter to my battery on the far side in about 12 ft. the negative is about 6 feet. so, yes double the distance, but the voltage drop is very, very small. My largest amp load will be quite small.

Next step is where to put fuse. i think ill ad a 150amp fuse to the terminal block of the batteries. i chose 150 amp because that is the amp rating of the 0/2awg wire.

the downside to the terminal block fuse is the batteries are underneath the floor of the van, and once cabinets are in, i will have to pull out drawers, then the floor to look at them.
 

Kevsuda

Member
Pull out the floor to see a fuse? I'm not sure what's involved with that. A fuse however inaccessible is safer than no fuse. That said, practicality is also important(to me), so an accessible place as close to the battery as you can get makes sense(to me). Even if that is an in-line fuse. One small touch of the +&- while doing maintenance or future installs is going to have you ripping your floor out. Maybe even a good marine breaker under there somewhere may be a good option?
 

marklg

Well-known member
I'm a big fan of MRBF fuses, and have one on each battery, sized for the rating of one battery. I have a Class T rated for the inverter cable elsewhere.

Pay attention to interrupt ratings of fuses. Search for that if you need to to see why.

Regards,

Mark
 

billintomahawk

'02 2.7 T!N Freightliner
Just did an elegant simple one, 100 amp house battery, 100 watt solar panel.
Cooking and cooling with propane. Refrigerator wiring is for controls only

Don't you fuse the inverter with a re-settable fuse.?

You could skip the B to B charge controller, I have in the last four lead acid systems I set up.
Just charge the house off the starter battery using a cheap marine switch to break the house ground to isolate it.

Hook your solar by pigtail(left partial box in diagram) to the house, it should have it's own charge controller to keep the house (and the starter if necessary) topped up.

I know what you are thinking but you will get 4-5 years of reliable power and lead acid batteries are cheap.





The fuse terminals are an easy place to grab power, go to house neg(-) for a ground(or chassis).

Guess I used 01/02 cable and 10 Gauge for the Aux fuse box.



bill in tomahawk
 
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i have a 150 amp breaker going from the house batteries to the inverter on the positive line. Should it be more?

I have a seperate fuse box that leads to all my lights/charge ports/power needs from my house batteries.

to me it seems overkill to have a 150amp terminal fuse, before the 150amp breaker to the inverter. Is there any reason i need both? Or will the breaker suffice?
 
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marklg

Well-known member
i have a 150 amp breaker going from the house batteries to the inverter on the positive line. Should it be more?

I have a seperate fuse box that leads to all my lights/charge ports/power needs from my house batteries.

to me it seems overkill to have a 150amp terminal fuse, before the 150amp breaker to the inverter. Is there any reason i need both? Or will the breaker suffice?
Any wire between the source (battery or charger) and the first fuse is not protected from a short. A short from a battery can be 1000 amps and pretty exciting. Since I have an inverter / charger, it can also supply current. That is why there is a fuse near each battery and a fuse near the charger. The charger does have internal protection, so that fuse is not right up next to it as I could not fit it there.

Fuses are sized for the max current the individual wire can take. So the fuse on each battery with 1/0 is smaller than the fuse on the 4/0 inverter/charger feed.

Regards,

Mark
 

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