Which material should I choose for a DIY LiFePo4 Battery terminal

[Aquivion]

Hello everyone,

I am a beginner and i just build my own 12V LiFePo4 Battery with a BMS. I build a wooden box around it and i want to attach negative and positive terminals to it, so that it functions like a normal LiFePo4 battery you can carry around.

I ordered some terminals which are made out of brass and installed them. The terminals just consist of a M8 brass thread, some M8 brass nuts and some plastic coverage. Everything works fine with them but there is a question I have in mind which i would like clarification on.

Now i looked up the electric conductivity of brass and I found out that it is almost 4x less conductive than copper. Afaik materials with a low conductivity are heating up more because of the higher internal resistance. Please correct me if i'm wrong here.

Some reviews from other buyers of the terminals stated that the terminals are heating up a lot when going up around 150Amps, pretty much melting the plastic that surrounds it. Although the advertisement states that they should work for up to 200Amps.

Now my question is (ignoring the fact for now, that the material heats up more if it is less conductive):

Does having a brass terminal or even a steel terminal have any downside to the rest of the system? I mean does the low conductivity / high internal resistance of the terminal have any effect on the copper cables that are attached to it?

Should I choose a different material with a higher conductivity for the terminal?

My feeling tells me, that it should not have any effect on the systems that is attached to the terminal, but would just like to be sure about this.

For me, it is no problem if the terminal heats up a little bit more (of course the terminal itself should not melt or anything like that, but I don't think I have to worry about this). I just don't want the terminal to have any negative effect on the system that is attached to it because of it's material.

Thanks i advance for any clarification on this!

 

[Zwy]

Less conductive is more resistance. More resistance is more voltage drop. More voltage drop equals more amps for the same amount of watts.

Throw the brass in the junk pile, it does not have a place in a system with high watt draws such as an inverter.

 

[Northernchateau]

These are the top 3 best conductors of electric are, copper, silver, aluminum.

https://www.amazon.com/dp/B0BJBZ5Y3F/ref=twister_B0BJBZDFTB?_encoding=UTF8&th=1

 

[Aquivion]

@Northernchateau Thanks for the answer, but won't I have oxidation problems with copper hex bolds? I found some aluminium ones here

https://www.amazon.com/-/de/dp/B07KCZ4855/ref=sr_1_2?qid=1668282140&refinements=p_n_material_browse%3A17548930011&s=industrial&sr=1-2&th=1

silver is hard to find. Gold would also be an option if I had a million dollars on my bank account ?

 

[Northernchateau]

@Northernchateau Thanks for the answer, but won't I have oxidation problems with copper hex bolds? I found some aluminium ones here

https://www.amazon.com/-/de/dp/B07KCZ4855/ref=sr_1_2?qid=1668282140&refinements=p_n_material_browse%3A17548930011&s=industrial&sr=1-2&th=1

silver is hard to find. Gold would also be an option if I had a million dollars on my bank account ?

Dielectric grease is your friend.

 

[justgary]

If your terminals allow you to connect the cable from the battery directly to another cable, the terminal stud material won't really matter as long as the cable terminations make good contact with each other. In other words, the stud material doesn't matter if the conductive cable ends make direct contact and with enough area.

 

[John Frum]

If your terminals allow you to connect the cable from the battery directly to another cable, the terminal stud material won't really matter as long as the cable terminations make good contact with each other. In other words, the stud material doesn't matter if the conductive cable ends make direct contact and with enough area.

I think @Aquivion is talking about feed trough terminals.

25: Feed-Through: Battery Junction Blocks and Remote Battery Jumper Terminals | Waytek

Battery Junction Blocks allow you to relocate battery terminals to a more accessible location. Remote Battery Jumper Terminals are in-stock and ready to ship!

www.waytekwire.com

 

[SparkyJJO]

Just A guess but they may be brass for durability reasons. A copper threaded terminal may not hold up very well but brass is tougher. The lower conductivity is a negative side effect though.

 

[Supervstech]

These are the top 3 best conductors of electric are, copper, silver, aluminum.

https://www.amazon.com/dp/B0BJBZ5Y3F/ref=twister_B0BJBZDFTB?_encoding=UTF8&th=1

Ya got ‘em out of order though…
It’s silver, copper, aluminum… gold is in between aluminum and copper… good for heat and corrosion, but not so great for conductivity.

 

[time2roll]

I use Anderson connector for the PTO. Commonly connected items get the connector. Have a set of battery clamps on a pigtail for unknown items. I like that the connection is insulated so if something moves around in storage there is low chance of a short.

https://powerwerx.com/anderson-power-powerpole-sb-connectors

 

[Aquivion]

@justgary Thanks for your answer. As @John Frum statet this was actually about feed through terminals, but your addition will still help me later in my system because i thought I would need to to have every distributor pole out of copper. But regarding that i have one question left:

Will cable lugs stacked on top of each other (with direct contact) share enough area? Assuming they're properly tightened together of course. Or should I use some copper washers inbetween maybe to increase the area?

Thanks

 

[Tony54]

I use Anderson connector for the PTO. Commonly connected items get the connector. Have a set of battery clamps on a pigtail for unknown items. I like that the connection is insulated so if something moves around in storage there is low chance of a short.

https://powerwerx.com/anderson-power-powerpole-sb-connectors

time2roll,
Im also building a box to house a 230ah, 24v battery and I like the Anderson connectors because they look neat, are insulated and make your box easily mobile.
I just glimpsed through you link hoping to find kits made up. That is with, say 18 inch cable and connector from battery to the box and one cable from box to battery cut off switch. From the big list of components it's difficult, for me, to know what I would need
maybe they do sell kits but I couldn't find one.
I will Google 200 amp Anderson connectors and see what comes up.
I also think the copper bolts have some merit and with copper washers and nuts should provide a cheaper and solid connection.

 

[SparkyJJO]

@justgary Thanks for your answer. As @John Frum statet this was actually about feed through terminals, but your addition will still help me later in my system because i thought I would need to to have every distributor pole out of copper. But regarding that i have one question left:

Will cable lugs stacked on top of each other (with direct contact) share enough area? Assuming they're properly tightened together of course. Or should I use some copper washers inbetween maybe to increase the area?

Thanks

Copper washers won't increase the area between two lugs since each lug is still only so big. Best case it won't do anything, worst case it creates more room for a bad connection.

 

[RCinFLA]

Conduction is not the only consideration. Inter-metallics interaction also needs to be considered.

Bare copper against aluminum battery terminals will pit corrode the aluminum terminal surface over time. A nickel barrier plating on the copper will prevent this.


Nickel is not the best conductor but if plating thickness is kept thin its degradation is not too significant. A typical 2 mm thick, 20 mm wide, 72 mm long, nickel plated copper core bus bar has about 0.07 milliohm resistance. Bare copper of same size is about 0.04 milliohms, but you have the aluminum-copper intermetallic issue. Same dimension bus bar with cheaper nickel-plated brass core has about 0.17 milliohms of resistance. You can file off the plating on end of bar to check color of base core metal. Brass has a yellowish color, copper is brownish.


A good clean clamped aluminum terminal to bus bar connection has about 0.05 milliohms of resistance so battery to battery terminal with nickel plated copper core bus bar will be about 0.05 + 0.07 + 0.05 = 0.17 milliohm resistance between cell terminals. That has less than 2 watts of heating at 100 amps of current. The battery terminal clamp resistance is the most common issue on DIY'er battery connections causing warm to hot battery terminals under moderate load current. A poor terminal connection will generate over 5 watts of heating which will get pretty warm to hot.

Aluminum surface exposed to air creates aluminum oxide which is an insulator that should be cleaned off with mild acid like 50% diluted white vinegar and cleaned with alcohol and dried before connecting terminal.

All this is very pertinent for considering your system battery voltage decision for given inverter wattage capacity. A 12v 3kW inverter with 275 amps of battery current is very difficult to deal with.

 

[time2roll]

time2roll,
Im also building a box to house a 230ah, 24v battery and I like the Anderson connectors because they look neat, are insulated and make your box easily mobile.
I just glimpsed through you link hoping to find kits made up. That is with, say 18 inch cable and connector from battery to the box and one cable from box to battery cut off switch. From the big list of components it's difficult, for me, to know what I would need
maybe they do sell kits but I couldn't find one.
I will Google 200 amp Anderson connectors and see what comes up.
I also think the copper bolts have some merit and with copper washers and nuts should provide a cheaper and solid connection.

I believe customcableusa.com may sell an assembly made to order.

https://www.customcableusa.com/coll...custom-battery-cable-marine-grade-by-the-foot

Call them. I don't see a click and buy for this.

 

[Tony54]

I believe customcableusa.com may sell an assembly made to order.

https://www.customcableusa.com/coll...custom-battery-cable-marine-grade-by-the-foot

Call them. I don't see a click and buy for this.

time2roll

Thanks for link, it looks like it's exactly what I'm looking for but it appears they only sell in USA, I'm in Spain.
By the time one buys a high power soldering iron and or a heavy duty crimper it would pay to have made to measure cables with connectors.

 

[justgary]

@justgary Thanks for your answer. As @John Frum statet this was actually about feed through terminals, but your addition will still help me later in my system because i thought I would need to to have every distributor pole out of copper. But regarding that i have one question left:

Will cable lugs stacked on top of each other (with direct contact) share enough area? Assuming they're properly tightened together of course. Or should I use some copper washers inbetween maybe to increase the area?

Thanks

To answer directly about feed through terminals, I bought "new, old stock" copper ones on ebay. They are rated to 500A and seem pretty beefy. They had black and red available.

https://www.ebay.com/itm/154795755924

 

[Tony54]

These are the top 3 best conductors of electric are, copper, silver, aluminum.

https://www.amazon.com/dp/B0BJBZ5Y3F/ref=twister_B0BJBZDFTB?_encoding=UTF8&th=1

Hi

Ya got ‘em out of order though…
It’s silver, copper, aluminum… gold is in between aluminum and copper… good for heat and corrosion, but not so great for conductivity.

Hi, I've decided to go with the copper bolts, so much cheaper and if using tight copper washers, there should be a good connections.

 

[rhino]

If we are talking about screws/bolts to use on these battery terminals there's nothing wrong with using stainless steel. You don't see any copper bolts or washers in any of the server rack batteries. Main electrical path is through the flat terminal pad and making sure that has a good long term low resistance interface between it and the busbar/lug.

 

[justgary]

Hi

Hi, I've decided to go with the copper bolts, so much cheaper and if using tight copper washers, there should be a good connections.

Pure copper is very soft and will not allow you to apply much torque without twisting the bolt off. Like @rhino said, use stainless bolts.