Cable Size for Shunt?

[J007]

Hello. I installed a Victron BMV-702 this weekend to monitor my two 6v golf cart batteries. After doing some research, I'm having a hard time figuring out what size cable to use from the negative on the battery to the shunt and then from the Shunt to the chase of my trailer. It looks like the trailer was wired with 8g wire to the batteries and then when the dealer installed the two 6v batteries before we picked up he used an 4g wire between the two batteries. The distance between the negative lead and the shunt is about 2 feet and then from the shunt to the current placement of the old negative to the chase is 4-5 feet. Could I just use 8g or 6g wire for the negative connections on the shunt?

[ScottBrownstein]

Might as well us 8Ga since the rest of the run is already that size.

[J007]

Scott thanks. Does it make a difference that the cable between two 6v batteries is 4g?

[ScottBrownstein]

Nope...they probably used that since it was all they had. 8 GA is kinda small, but putting in 5 feet of larger won't make any significant difference since the rest of the run is #8.

[J007]

Great! Thank you very much, this is very helpful.

[Tom48]

Originally Posted by J007

Great! Thank you very much, this is very helpful.

I am curious as to the shunt amperage you used.

Also not much benefit in increasing the size of the grounding run but larger is always better. If you are having to run new wire with the install I would definitely up it to 4 ga which I buy pre fab'ed from AutoZone at a reasonable price.

The cable between the two batteries is to tie the two and make them one. I tied mine with 2 ga even though the feed to my coach is only 6ga. I definitely don't want the start out with ANY LOSS , especially when I am wanting max out put from my shiney new GC2 Batteries.

[270S]

Originally Posted by J007

Scott thanks. Does it make a difference that the cable between two 6v batteries is 4g?

Answer is explained here ZRD FAQ - Wire sizing for all situations!

Manufacturers undersize wire!
If the run was 500' would you still use 4 or 8 awg - NO. Size is a function of length. ALAWYS use a 3% or less voltage drop.

[B and B]

Hello, That shunt will be in bad shape with water and any corrosive road treatments. I would mount it some place weatherproof.

[ScottBrownstein]

Originally Posted by 270S

...ALWAYS use a 3% or less voltage drop.

Absolutely true. The OP has two 6 volt batteries, at most that is 225 AH at 12 volts (112 usable) A short length of 4 or larger isn't going to make a difference when he already has 20 feet of #8 in his circuit. While it is true that distance matters, a 12" length on a 20 foot feed doesn't matter much, even if it had a resistance of zero! If he is planning on upgrading in the future it might make sense but it won't do anything for him right now.

Manufacturers don't undersize wire, they run wire that is approved for the ampacity of the converter, regardless of distance. Doing that they are legal...but waste a tremendous amount of power in voltage drops. As I have previously said, my 335 has a 70 amp converter that is 22 feet from my batteries and they used #6, which is rated for...75 amps. Of course, I never see 70 amps since the feed loses almost 9 percent at 70 amps, dropping boost to 13.28 volts if that high.

[J007]

It's a 500a shunt and mainly just looking to hook negative back up from battery to chase. Longest run would be four feet. The wiring and voltage loss is very new to me, so this is helpful. I understand bigger would be better, but if there isn't going to be that much difference, utill I decide to rewire, if sticking with the 8g is fine it may be easier.

Also, I spent the weekend going from place to place looking for a good case to mount the shunt in, but couldn't find anything that would fit 5" x 3" and still allow me to fit wires. So I mounted it on underside out of the way of weather. If need be and I fine a box to fit, I'll definatly change it.

Thanks all for your help.

[5picker]

Originally Posted by J007

It's a 500a shunt and mainly just looking to hook negative back up from battery to chase. Longest run would be four feet. The wiring and voltage loss is very new to me, so this is helpful. I understand bigger would be better, but if there isn't going to be that much difference, utill I decide to rewire, if sticking with the 8g is fine it may be easier.

Also, I spent the weekend going from place to place looking for a good case to mount the shunt in, but couldn't find anything that would fit 5" x 3" and still allow me to fit wires. So I mounted it on underside out of the way of weather. If need be and I fine a box to fit, I'll definatly change it.

Thanks all for your help.

I've got a lot of outdoor stuff weatherproofed by using snap lock food containers. Available inexpensively about everywhere.

[Swampweasel]

Amazon has a large selection of waterproof boxes to choose from. I think this is the one that I used for my Victron shunt:
https://www.amazon.com/Waterproof-Cl...waterproof+box
Just search for waterproof box on Amazon.

[J007]

Thank you both.. It looks like I should have turned here first before running all over this weekend. I really appreciate it.

How do you like your Victron?

[270S]

I have 2 monitors. 1 is inside the rear pass through for my installed battery bank - no need for wp box. Other is by steps for GT installed BB (to be replaced when it dies). This one is inside a grey wp box from Lowes for apc $10.

[270S]

Remember Rating is for fire NOT efficiency. I always up 1 or 2 wire gauges after I calculate correct size - even though it is not required for fire or 3% rule. From 40+ years of experience, Everything just works better that way. I'm on the 1% or 0% rule scenario.

[Swampweasel]

I really like my Victron. Being the gadget nut that I am, I just bought the Victron bluetooth dongle and I can now monitor my battery from my smartphone using the Victron app.

[J007]

That funny, I bought the blue tooth dongle as well, so I could moniter the status from in my house.

[Tom48]

Originally Posted by J007

It's a 500a shunt and mainly just looking to hook negative back up from battery to chase. Longest run would be four feet. The wiring and voltage loss is very new to me, so this is helpful. I understand bigger would be better, but if there isn't going to be that much difference, utill I decide to rewire, if sticking with the 8g is fine it may be easier.

Also, I spent the weekend going from place to place looking for a good case to mount the shunt in, but couldn't find anything that would fit 5" x 3" and still allow me to fit wires. So I mounted it on underside out of the way of weather. If need be and I fine a box to fit, I'll definatly change it.

Thanks all for your help.

The point of my asking about the shunt was curiosity. They seem to offer 100 amp or 500 amp shunts and I will be getting the 500, but you are not likely to ever pull 100 amps over 8 gauge wire.

Remember that the ground leg IS HALF the flow to the house. If you can, go big, cause will come the day you will want more than 8ga to you converter and you will be upgrading the POS side.

And yes, that Shunt will not fair well exposed like that. Have looked at regular outdoor boxes in the building supply like you would use for an outdoor outlet or switch. I have adapted those for my solar system at home and looks like a single gang box would fit there.

Good luck. One step at a time. Next if you have not yet done so, should be 200 watts of solar.

[J007]

Thanks... I think I found a few boxes now, thanks to everyone. I agree one step at a time otherwise my DW might leave me. Funny you mention solar because the 200w was what I was thinking would work well with my setup.

[ScottBrownstein]

Originally Posted by J007

Thanks... I think I found a few boxes now, thanks to everyone. I agree one step at a time otherwise my DW might leave me. Funny you mention solar because the 200w was what I was thinking would work well with my setup.

...and #8 will be just fine for 200 watts of solar!