High voltage wire, crimp connectors, and not dying

[Tremelune]

I'm in the process of converting a Rover Mini to an EV using a Nissan Leaf. I'm at the point where I'll need to start doing some high voltage re-wiring to relocate the batteries and power module. I'm handy with crimpers and soldering irons, and I've worked with thick wiring for high-power 12V audio, but these orange high-voltage wires are new to me...I'm trying to figure out what the differences are between 12V wiring and 400+V wiring.

It's hard to find information, as "high voltage" usually means 1kW and above, whereas I'm working with a maximum of 400V in a Nissan Leaf pack. I either find household wiring info or 12V wiring info. I know P = A * V, but are there any other considerations? Are gauge calculations the same from DC to AC? How do I know how much insulation is safe at a particular voltage? I'd like to err on the side of too large a gauge for the power needs, just to eliminate it as a potential source for reduced performance (and future proofing).

- Can I use standard marine/auto/audio wiring for 400V without degrading performance or increasing danger?

- Is there anything special about crimping or soldering HV wire I should know about (vs 12V wire)?

- If I do need to buy wire and tools for this purpose, what's the good stuff? I usually buy marine-grade wire from Waytek for my stereos and what not. I found some stuff at EV West, but I can't say I understand the difference between the EV West cable, the Hew-Kabel cable, and Champlain EXRAD XLE cable...I have a bolt-cutter-style crimper that goes up to 1/0.

- When is it okay not to wear my 1000V rubber gloves when working with these batteries? Like, what can I touch when? Though I've melted a wrench across a 12V battery, most issues there are avoided by disconnecting the ground and not touching any power terminals.

 

[amberwolf]

- Can I use standard marine/auto/audio wiring for 400V without degrading performance or increasing danger?

You must use wire that has insulation rated for *at least* the full charged voltage of your pack. I recommend overdoing it if you're not sure.

If you use wire with insulation rated lower than that, it could break down and pass current outside the wires, where you don't want it. What happens at that point depends on the situation, but it's hardly ever good.

Double insulation is a good idea, too, so that should something fail in the actual conductor's insulation, you have an outer jacket on it (also rated for at least the full voltage), to prevent problems. And/or the jacket can prevent physical damage to the conductor's insulation from vibration, etc.

- Is there anything special about crimping or soldering HV wire I should know about (vs 12V wire)?

I would recommend using the stuff that is for the HV specific wiring market (if there is any), that *also* fits the high current (hundreds of amps) market. Looking at existing *complete and tested* builds in the voltage and current range of your project, to see what they did, would be one way to find usable stuff. If it's not complete and tested, you won't know if what they used works, so.... There are more threads on the forum you linked to than there are here, for such HV stuff, but there's a few. JonesCG's race bikes are HV, in the range you're after, for example.

Your connections must handle *both*, without even noticing. You don't want any significant resistance in the wiring or especially the connections, as they will heat up under load if they do. If there's enough heat, the plastic housings can fail, and then short circuits can occur, which can result in fires.

I expect most poeple with experience at HV/HC stuff are going to recommend crimping only, no soldering. One issue with soldering wires is that it makes the wire beyond the joint very stiff, not flexible, and vulnerable to stress fractures from vibration over time. Thick wires are already stiff, so this can exacerbate the problem.

- If I do need to buy wire and tools for this purpose, what's the good stuff?

There are a number of threads about connectors/crimpers/etc., but most of them deal with low voltage stuff. The threads for the completed projects will probably have more usable info on what they used, but not all of htem actually say. :/

- When is it okay not to wear my 1000V rubber gloves when working with these batteries? Like, what can I touch when?

If you have any exposed connections or conductors, it is much safer to always use precautions. All it takes is one moment of inattention, one distraction, and you can end up acting as a system bypass.

I've zapped myself even with a 58.8v 14s battery, just by accidentally slipping with a probe while checking balance. The probe was fully insulated, except teh pionty tip's last millimeter...but my hand wasn't, and it was hot, I was sweaty, and my natural reaction to grab the probe resulted in placing the edge of my hand across a number of cell interconnects in the middle of the pack. I didn't touch them long, and it wasn't more than maybe 20-30v, just a few cells...but it was enough to set off quite a tingle that lasted for a while, in my arm. If it had been a pack that zigzags back and forth for connections, and I'd bridged end to end, it'd really have hurt. If it was an HV pack built that way, I could've had severe injuries.

 

[john61ct]

40-50V is where fatality becomes much more likely.

But lots of variables of course, for details google the EU's Extra-low voltage (ELV) and Safety Extra Low Voltage initiatives lots of 101 level explainers out there.

But EV stuff is almost always super high risky, so the less you know compared to how much you think you know - early stages Dunning—Kruger - the more careful you should be.

 

[Punx0r]

A lot of industrial mains power is in the 400-480V AC range and mega amps. The crimp lugs for this are the same as you'd find used on 12V DC. The difference is, unlike a 12V system where you might have a rubber boot for insulation that can slip off, it's all hidden away inside plastic or grounded metal enclosures fitted with cable glands so there's no way you can come into accidental contact with the terminals.

Notwithstanding what amberwolf said about insulation ratings, for the conductors/lugs/terminals themselves the voltage doesn't affect the current they can carry. It's amps that cause heating and amps is amps. Soldering doesn't belong on high current connections, it's not as strong or reliable as a proper crimp. Take a look at a photo of a sectioned hydraulic crimp and see how the cable and lug are practically fused together as one solid lump of copper.

 

[Tremelune]

Thanks! My take-away is that everything is pretty much the same, but with "Low Voltage" (50-1000V AC, 75-1500V DC):

- Use wire with sufficient insulation for the maximum expected voltage, regardless of current (or it might arc).

- Amps are amps regardless of voltage, and that amperage requirements determine wire gauge.

- Respect the zap of large, chained batteries, and go through the hassle of rubber gloves when poking around in there.

Two questions:

1) Is there a site I can find quality 600V wiring for the US that is cheaper than EV West?

2) What should I do about insulating butt connections for Low Voltage wiring? Seems like I'd need some pretty thick heat shrink...I'm not sure just wadding it up with electrical tape is the best plan...

 

[Punx0r]

When you say low voltage butt joints are we still talking 400+V?

 

[john61ct]

Butt splice connectors are a standard termination, or ring terminals to a buss bar

Marine spec fine stranded tinned-copper is trustworthy, size for the amps.

This site has some great articles on proper crimping.

https://marinehowto.com/marine-wire-termination/

Get genuinedealz.com to do custom cables, great quality, reasonable pricing.

 

[Tremelune]

When you say low voltage butt joints are we still talking 400+V?

Yep, sorry—I suddenly witched to the EU definition of Low Voltage - 50-1000 VAC, 75-1500 VDC.

 

[liveforphysics]

40-50V is where fatality becomes much more likely.

Thats just not true for skin contact shocks, only if you stick the wire through your skin.

If you're shocked with the current path across the chest at 300-400Vdc, you have a strong dice roll for it being your last earthly sensation. Best case, the contracting muscles get torn/damaged. Strong shocks for me typically dislocate my ribs and leave my pectoral and biceps ripped up, and give a few minutes of irregular heartbeat. This is getting off lucky.

The obvious risks are not to touch the metal conductors, and to use double or triple insulation everywhere critical (because its so easy to chaff through a single layer).

The less obvious risks are where your harnesses drip loop paths look like with respect to getting soaked and conducting along/through unexpected places.

I would recommend harnessing everything up completely before ever connecting the pack to be live voltage, and hi-pot your system at at least 5x your intended long term operating voltage. If it passes (which isn't that hard), the spray down every surface that would get wet during use (driving in rain etc), and re-hi-pot with it all soaking wet. Once you confirm no isolation leaks to chassis or other unexpected places, you could spray it all with a salt brine solution and wait a few days and hi-pot again. If you're able to pass all that with 5x system design voltage, then clean everything up as best as possible, and you've got a shot as a safe system.

 

[Punx0r]

Bear in mind what knowledge I have is based on industrial rather than EV wiring, but the real solution would be to avoid any butt-joints. For splicing a large cable commercially you'd used something like a resin-filled "boat" joint. Otherwise I'd take cables into an IP65 enclosure (with glands) and join inside with a screw terminal block or crimp connector inside. The enclosure and glands provide the insulation and strain relief.