1
\$\begingroup\$

I have four batteries in series, 48v and a 500amp controller.

Right now, I am using standard amplifier battery cables, I believe they are 0 gauge.

Operational performance is not as good as suspected and the controller and wires seem to get very hot at peak amps and today a lead terminal sheared itself off under constant load.

I am guessing my wire is insufficient for carrying such a load.

If so, what should I use?

Additional information per comments:

I didn't expect to move to 500 A, I was pushing 200 A for a while and upgraded the controller. The application is a finished electric motorcycle, but I live on a mountainous area so the amperage is sustained longer than usual.

Would you recommend aluminum over copper?

The way each battery is mounted won't allow for busbars to be used.

Really hard estimate the wire length everything is mounted tight, no wire is more than 12", most being around 6"

I do notice voltage drop during higher amp loads but I think that's to be expected anyways during acceleration

The connections are made of lead, they're automotive grade electrical wire, like what connects to a starter. Fine for 200a maybe not for 500.

\$\endgroup\$
26
  • 3
    \$\begingroup\$ Another term to google is "bus bar". \$\endgroup\$
    – The Photon
    Commented Jan 24, 2017 at 23:53
  • 2
    \$\begingroup\$ 0 gauge can only carry about 150 amps safely. You need 900 MCM or so depending on insulation type. You also need to consider the length of the wire. Voltage drop could be a problem if the length is too long. That seem like a lot of sustained current for just series connected batteries. \$\endgroup\$
    – user80875
    Commented Jan 25, 2017 at 0:18
  • 2
    \$\begingroup\$ Rule of thumb is 1mm² per 10A. For short cables you may use less as the voltage drop is more at the connectors then. \$\endgroup\$
    – Janka
    Commented Jan 25, 2017 at 1:36
  • 2
    \$\begingroup\$ Note that the high temperature wire is rated for higher current, but it could run too hot for the battery and controller terminals. \$\endgroup\$
    – user80875
    Commented Jan 25, 2017 at 1:39
  • 2
    \$\begingroup\$ @CharlesCowie: Aluminium conductors are dangerous when they are fitted wrong. Even welded aluminium contacts may fail miserably. Noone but power grid people should use aluminium conductors. They have the right tools and know what they are doing. \$\endgroup\$
    – Janka
    Commented Jan 25, 2017 at 1:39

3 Answers 3

1
\$\begingroup\$

2/0 copper with 90C insulation is good for 195 amps. For 75C insulation you need 3/0 and 4/0 for 60C insulation. Those are electrical code requirements for building wiring for conductors bundled into a cable or conduit. Ratings are based on air temperature not exceeding 86F.

I would strongly recommend copper wire. Aluminum is cheaper and lighter, but more difficult to work with. Special wire terminals are required with a special tool to attach them to the wire. Some kind of special grease needs to be applied at the termination.

For this application, I would recommend diesel locomotive cable (DLO) or copper welding cable. If it only comes with 90C insulation, I would oversize the wire so the terminals don't get too hot. Both of these types of cable are more finely stranded than typical stranded wire. That makes the wire more flexible and allows it to make better contact with terminals.

In this application, the largest part of the voltage drop is likely the internal resistance of the batteries. The voltage drop of AWG 0 wire is about 0.05 volts per foot at 200 amps. AWG 2/0 would drop about 0.04 V/ft and AWG 4/0 about 0.03 V/ft.

The voltage drop in the connections depends on the contact area, the smoothness of the contact and the pressure of the connection. The best wire terminals are probably the kind that is compressed permanently around the wire using a special tool. For wire this size, you should only use quite a good quality tool. The type of terminal that compresses the wire with a screw is easier to use. For best results, look up the torque specification for the terminal and use a torque wrench. Your controller may have that type of terminal built in, or it might have studs or holes to attach wire terminals. If the motor has leads rather than terminals, you will need screw compression wire splicers that you need to tape up to insulate the splice. Depending on the type of battery and the terminals it has, you may want to look for battery terminals that have either holes to bolt to ring terminals or compression terminals for wires. Make sure the terminals are rated for the size wire you are using and tighten them to specifications with a torque wrench.

If your controller has wire compression terminals, don’t use a larger wire than the terminals are rated for and tighten them to specifications with a torque wrench.

Here are pictures of appropriate terminals, wire splice and terminal crimping tool.

enter image description here enter image description here

\$\endgroup\$
2
  • \$\begingroup\$ The wire and ends arrived today, and I have already begun rewiring. Thank you so much! \$\endgroup\$
    – Matth3w
    Commented Jan 26, 2017 at 3:52
  • \$\begingroup\$ I rewired everything today and MANNN what a difference, the bike is a ROCKET now and no more heat issue. Your advice really helped, thank you. \$\endgroup\$
    – Matth3w
    Commented Jan 27, 2017 at 7:35
1
\$\begingroup\$

For low voltage work, the voltage drop per length is often critical. You say it's a motorbike, so let's assume connections are 1m long. If you have a radically different length, then you can just modify my answer proportionally.

What would you consider 'good'? With 48v available, losing 1v in the wiring is 98% efficiency, probably a reasonable place to start. Of course the wires go there and back, so you want 0.5v drop per wire.

At 500A, a voltage drop of 500mV requires a wire resistance of 500m/500 = 1mohm, nice round number. As copper has a room temperature resistivity of 17mohm per 1m of 1mm2 wire (numbers I always have in my head), then you need at least 17mm2 wire, for that voltage drop.

The power being lost in each wire is 0.5V * 500A = 250 watts, which is probably excessive. So it looks like heating, and not voltage drop, is the limiting factor at 48v and this distance. Certainly the 10A/mm2 rule of thumb for low currents suggests 50mm2 area, and at 500A, we would tend to tun at less than 10A/mm2, as for a single wire, there is proportionally less surface area available for cooling. Certainly 'normal' wiring regulations would expect something like 250mm2 for a single core 500A wire.

As you increase the area, the voltage drop and therefore power dissipated falls proportionally.

If you can make the connections as a parallel set of smaller wires that are not bundled together, then cooling is improved, and more current can be carried.

Now we can draw up a crude table, of heating power versus cross sectional area for 1m connections at 500A. Pick a suitable pair of numbers, interpolation to standard sizes is obviously trivial.

area    power per wire

17mm2    250W
34mm2    125W
68mm2     63W
136mm2    32W
270mm2    16W
\$\endgroup\$
2
  • \$\begingroup\$ I already said no connection is more than 12"; all but two are 6" \$\endgroup\$
    – Matth3w
    Commented Jan 26, 2017 at 3:51
  • \$\begingroup\$ I answered the question before you added that later. I figured if it wasn't important enough to tell us first off how long the connections were, then you wouldn't have any problem scaling them. Did you see I already said 'if 1m is wrong, then scale'? \$\endgroup\$
    – Neil_UK
    Commented Jan 26, 2017 at 7:47
1
\$\begingroup\$

You are deep into busbar territory at 400 A. You should consider multiple wires unless you want to get into very large cables.

Amp capacity of wire is generally conservatively rated at 700 circular mils per amp as in this table.

You could use multiple automotive primary wire connections. This is good multistranded insulated wire that is flexible enough to route. You'd need 4-5 cables for 400 A continuous.

Or if you could use uninsulated cable, then automotive earth braid might be a good choice. If your cables are only a few inches long, this might be the ideal choice as a single run would support 380 A continuous, and well over 400 A burst. You could put loose insulation covering over it.

\$\endgroup\$
4
  • \$\begingroup\$ Jack - you (or Murphy) have posted nearly identical duplicate answers. \$\endgroup\$
    – Russell McMahon
    Commented Jan 25, 2017 at 6:02
  • \$\begingroup\$ So that's what the Post twice button does.... \$\endgroup\$ Commented Jan 25, 2017 at 6:26
  • \$\begingroup\$ :-) Redolent Redundancies there, that's > 15. \$\endgroup\$
    – Russell McMahon
    Commented Jan 25, 2017 at 7:35
  • \$\begingroup\$ Problem already solved. \$\endgroup\$
    – Matth3w
    Commented Jan 25, 2017 at 8:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.