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My MotorHome LiFePo4 build and bus bar questions...

Rocketman

Solar Wizard
Joined
Sep 27, 2020
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Hello Everyone!

This spring I will be installing 8 Lishen 270ah cells 2p4s into my MotorHome giving me a 12v 540ah battery (Hopefully useable of 500ah) . My batteries are ordered and I already have most of the other accessories I will need. I have a Batrium bms and it will be controlling a Kilovac EV200AAANA contractor. My biggest question right now is the bus bars on the battery. Please double check my thinking... I have a tenancy to overthink a lot of things (a lot!).

The two largest draws on the battery will be a first, a Victron 12/3000 inverter/charger. This should have a max draw of 250ah (maybe more if in surge mode). Second, I am also wanting to keep the emergency boost ability of the MotorHome. There will be a 400a Class T fuse protecting the battery - so hopefully if I ever need the boost, the starter will use less than 400a (or there goes a $35 class T fuse). Like most RVer's I don't expect to use the full power of the inverter or boost very often - if at all.

So to the bus bars... As part of my design both the positive bar & the negative bar coming off the battery will have a 90 degree bend in them. (Shunt & fuse will be mounted vertically on the outside of battery box). So I will have to heat and bend over the bus bar.

I have 2 choices of bars:

First, I was thinking of using copper bars from onlinemetals .125 x 1" (1/8" x 1"). The charts I found says that will handle 270amps @ 30C rise (and 360a at 50C rise and 415a at 65C rise). Since anything around 250amps will be very short-lived, I think that will be OK. Stainless Steel Studs into the aluminum battery post (with red permatex or purple loctite) and a nord-lock washer & ss nut on top and it is ready. Issue - different metals & corrosion.

Second I was thinking of Aluminum bus bars .250 x 1" (1/4" x 1"). The charts say this will handle 300a @ 30C rise. I like this idea, of aluminum post, busbar and fastener, except I cannot find any M6 aluminum posts - so I would probably put the stainless nut all the way up the aluminum bolt, add the nord-lock washer, then through the aluminum bars and into the aluminum posts (w/ red permatex or purple loctite). The bolt head will stick up over everything else, with the nut that holds everything down a bit lower. I like this method because everything is aluminum (except the lock washer and nut), so hopefully there will be no corrosion issues and if so it is a replaceable bolt probably 3/8"+ away from the battery posts.

I have read several posts about using the copper bus bar and no one seems to be really concerned about the dis-similar metals.

So am I overthinking it again...

Does anyone see any other issues with these plans???

Which would you choose - aluminum or copper bus bars?

Thanks for your ideas

Rocketman
 
Does anyone see any other issues with these plans???

Which would you choose - aluminum or copper bus bars?
You are over thinking things! I would prefer copper 1/8 x 1 , easy to bend if needed. Unless you are in a marine environment or very humid conditions dissimilar metal problems will be non existent. Use a trace of the anti oxidants on the contact areas as often suggested. Use all stainless fixings, studs and nuts/washers.

Mike
 
I am still researching both ways to make bus bars (Copper & Aluminum).
I ran into something a bit unique while looking for the aluminum fasteners Motorcycle Bolts!

ProBolt-usa.com sells anodized aluminum bolts , washer & nuts & lock-nuts (in like 7 different colors). I am thinking about using a socket cap bolt M6-1.00 x 30 (&40)mm. running a nut up the threads, adding the washers, and through the bus bars and into the batteries it goes. set the proper depth on the cap head bolt - hold it there and tighten the nut down to hold everything down. Then once everything is set use a sharpie marker to mark where everything was tight so I can tell (at a glance) if something has started to vibrate loose.
 
If the stiff busbar bolts directly to battery terminal (which can't take much torque), how do you ensure wiggling of busbar doesn't loosen bolt?

I'm using AGM which have copper terminals, probably stronger. I have a 10" 4/0 cable off the battery to busbar (or fuse holder, in case of positive.)
 
Tin plated copper will not react with aluminum terminal pads. A bit of grease will protect fully.
 
But first, remove the native oxide which grew on bare aluminum terminals of the cells.
 
Is aluminum bus bars a problem? One very good aspect is price. Copper is like $12/ ft plus freight - so several feet and your looking at $70 to $80

Aluminum bar 1/4” x1” I can get at local big box. $28 for 8 feet (hopefully I can find a 4’ piece).

if I polish the alum bar where it will contact the batteries or other alum bars add some anti ox... I can have it all aluminum.

Is that better? or because copper flows power better - copper is better, despite its costs.

All the unknowns...
 
Such a deal?

How about 1/4 x 1" x 4' for $7? (probably $7 shipping, through)


Aluminum, just scale up cross section according to conductivity.
It is usually more prone to fractures, and has electrical failure where necked down. See about making large radius bends around a pipe.
Use all tinned terminals where wires attach, avoiding bare copper.

But again, long bar applies bending moment and torque to terminals, could damage or loosen. Why not connect a limber cable instead?
 
I used these cables to connect my 8 AGM batteries together and to busbar/fuse holders


Some people have made flexible busbars to connect cells with copper braid.

The idea was to accommodate expansion or motion without putting stress on terminals.
I used a short busbar with several cables bolted to it.
 
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