Building an EV motorcycle. Batteries: Need opinions.

[Ryland]

Originally Posted by TurnNBurn

This will be my first electrical project. I've had a lot of experience with fixing things mechanically (transmissions, engines, etc...) but this will be my first wiring project. What gauge of wiring would you guys recommend for the main battery setup? (wiring batteries, controller, and throttle)

Draw up all of your parts and make a diagram or a list of what needs to connect to what and what I did for my motorcycle was to make a wiring harness for the smaller gauge wiring and labeled everything, I partly did this because I wanted to bench test the battery management system before installing it on the frame, but at the very least a list of what connects to each component helped me a lot.

I checked some online wire size calculators and figured that for around 6 feet of cable at a peek of 400 amps but a sustained 150-200 amps that 4 gauge cable would be fine, auto parts stores should have bulk red and black cable, I really like welding cable because it's finer strands of wire so it's softer and more flexible, McMaster Carr has Heavy Duty welding cable that has bright orange insulation so I bought 10 feet of that for my motorcycle, it looks good and it's clear that it needs extra caution, I then bought red and black heat shrink tubing with hot melt glue inside (dual wall or dual layer) so I could color code all of my high current cables, I also make notes with white out pens (fine tip paint pen) as to what things are, like "Battery +" and "Controller M-" to make sure that I could not screw things up while assembling if I wasn't thinking clearly that day.

Another trick that I liked that I feel made my motorcycle cleaner in wiring it was for stuff like wiring in the DC to DC converter I slipped the end of a 14 Gauge piece of wire in with the welding cable along with a piece of 8 gauge wire for the charger before I crimped the lug on and I left those smaller gauge wires a foot or two longer then needed to allow me to bundle all my wires together to keep things tidy, if you aren't sure if you need a small gauge piece of wire on the positive and negative ends of your battery pack then you might just do a short pig tail with a push connect wiring connector that has the plastic shielding around it, that way you can add on later.

Repair shops that work on semi trucks tend to have decent crimpers for making battery cables, hammer crimpers work... kind of... but crimpers that press from multiple directions do a much better job, giving a pressure weld to the connection.

If you are going to draw more then a peek of 400 amps or have a longer run then 6 feet or so total of battery cable then go with a larger size cable, on a motorcycle tho you can keep everything close.
For wiring between the pack and the dc to dc converter I used 14 gauge wire, because I had that on hand I used it for a lot of other stuff as well, for the charger I used 8 gauge with an Anderson connector.
For the throttle, the twist throttle comes with it's own wire.
To power contactors, you are only drawing a few watts, so 16 or 18 gauge wire would even work.

[rmay635703]

Originally Posted by Ryland

I checked some online wire size calculators and figured that for around 6 feet of cable at a peek of 400 amps but a sustained 150-200 amps that 4 gauge cable would be fine, auto parts stores should have bulk red and black cable, I really like welding cable because it's finer strands of wire so it's softer and more flexible,

If you are going to draw more then a peek of 400 amps or have a longer run then 6 feet or so total of battery cable then go with a larger size cable, on a motorcycle tho you can keep everything close.

Chicken wire (small cable) can be irritating though because its easier to break (and wear out) My c-car is a rats nest of white 18 gauge, very irritating, a variety of "components" are no longer functional and I have no idea why they are wired, but alas his is a new one not a 3 previous owner kludged special.

Also, although I recommend the biggest gauge (numerically smallest) you can handle in any EV conversion, if he has the wire or its real cheap I would estimate that he could get away with very light gauge wires 6 or 8 gauge.

DC applications are not like AC in that you have a time variable in there and voltage drop is "less" important.

So even if he peaks over 400amps, on a motorcycle the duration would be minimal and likely his run time is also minimal, so he could get away with light stuff just because he would be within the 1hr rating for the material averaged out.

This saves a tiny bit of weight and potentially a a fair amount of cost, but he would loose a few percentage points on his efficiency mainly at high loads. He also might loose durability if the cable is not properly rated for vehicle use and rubs which to me is more important than the gauge, one reason why I have 0/3 welding wire even though I probably only need 4 gauge in here too.

I would say though that he better make sure battery interconnects are ALWAYS top notch, its the longer runs to the controller and motor that can be cheaped out on.

Kind of like the 80's GM vehicles with a 60amp alternator and 12 gauge wires.

[Ryland]

DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk

That is the cable sizing calculator that I used, with 5 gauge (what the calculator gave me) at 400 amps, 72 volts will drop to just under 70v if you have 3% loss in your cables, so of the 28,800 watts the batteries would be putting out at that point in time, 800 of those watts would be turned to heat, once you hit cruising speed and are drawing 100 amps or so you could have 6 gauge wire and only loose 1%, so while I agree with Ryan that larger cable is better, there is something to be said for spending less, having less weight and having the cable take up less space and being easier to route, that is why my Commuti-car (same make as Ryan's) has been upgraded from the factory 4 gauge to 2/0 cables, of course it draws near 600 amps peek and has over 25 feet of battery cable.

[TurnNBurn]

Originally Posted by Ryland

DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk

That is the cable sizing calculator that I used, with 5 gauge (what the calculator gave me) at 400 amps, 72 volts will drop to just under 70v if you have 3% loss in your cables, so of the 28,800 watts the batteries would be putting out at that point in time, 800 of those watts would be turned to heat, once you hit cruising speed and are drawing 100 amps or so you could have 6 gauge wire and only loose 1%, so while I agree with Ryan that larger cable is better, there is something to be said for spending less, having less weight and having the cable take up less space and being easier to route, that is why my Commuti-car (same make as Ryan's) has been upgraded from the factory 4 gauge to 2/0 cables, of course it draws near 600 amps peek and has over 25 feet of battery cable.

Neato. Thanks for that link and info. I'm going to look into cabling a bit further. First I need to get batteries picked I think. That way I know how may volts and amps and amp hours are flowing.

Motor should be here Thursday and I got my Magura throttle grips in. Last thing I need now is cabling and batteries and I'm riding. (oh, and a motorcycle class license)

[TurnNBurn]

Actually, I overlooked something. Battery management systems and chargers. If I'm going with Lifepo4 batteries, do they have integrated BMS or is there an external one you'd recommend?

I was looking at the Winston batteries (Electric Motorsport EV Parts) 3.2v 90 Ah.

I actually had another question regarding the amp hour. Do you guys think the 90 Ah is worth the extra money over the 60 Ah? Do you know the math on figuring out how to estimate total range with the extra 30 Ah?

Nevermind. I found it: Sizing your Battery Pack - DIY Electric Car Forums

[rmay635703]

Originally Posted by TurnNBurn

Actually, I overlooked something. Battery management systems and chargers. If I'm going with Lifepo4 batteries, do they have integrated BMS or is there an external one you'd recommend?

I was looking at the Winston batteries (Electric Motorsport EV Parts) 3.2v 90 Ah.

I actually had another question regarding the amp hour. Do you guys think the 90 Ah is worth the extra money over the 60 Ah? Do you know the math on figuring out how to estimate total range with the extra 30 Ah?

Winston are some of the best for hobbiest use given their nice cost/ahr.

But...

It really depends on your needs and the platform you are building off of.

If you are talking low voltage AKA 36v-48v, 90ahr would be great for a decent range but if your talking higher voltage I don't think it would fit in quite as nicely. Unless you have a heavier platform to start with.

Something else to note, (although more expensive per WTHR) is that for motorcycles BB30's and NiMH Hybrid battery packs can be used instead. These can be had for a couple hundred per complete pack (if you look/wait) but weigh more, are high voltage but also can last longer and can be easier to charge.

Many will lambast me for said statement above but I think it really depends. If you can locate a cheap Ford escape hybrid pack locally it makes a great starter pack, can be paralleled if you use motor run diodes and separate chargers and can last longer than lithium in more extreme use and during more extreme weather (aka it handles cold well).

The only real reason to consider the NIMH however is to avoid a complex BMS and reduce the likelyhood of pack death. If you are anal you can probably get away with lifepo4 with no BMS but if you are not and tend to not pay attention NiMH can be more forgiving (usually).

I am still on junkyard lead for the moment and likely for a good time in the future but this was due to some negative lithium experiences so my thoughts may be jaded but care should be taken when you take the lithium plunge.

Also my previous statement about larger than needed cables was that I prefer to use them (you can run an 0/3 with half the conductor coroded away and still not zorch)
but that in your case you might get away with even lighter wire than the calculator mentions depending on how long and how far we are talking and what your actual cruising amps really are.

I would hope a motorcycle would be quite low.

Good Luck
Ryan

[TurnNBurn]

Originally Posted by rmay635703

Something else to note, (although more expensive per WTHR) is that for motorcycles BB30's and NiMH Hybrid battery packs can be used instead. These can be had for a couple hundred per complete pack (if you look/wait) but weigh more, are high voltage but also can last longer and can be easier to charge.

This is the first I've seen NiMH suggested for a motorcycle. Do you have any online vendors you'd recommend I check out? Also, are these the smaller packs like you'd find Lipo packs?

[rmay635703]

Originally Posted by TurnNBurn

This is the first I've seen NiMH suggested for a motorcycle. Do you have any online vendors you'd recommend I check out? Also, are these the smaller packs like you'd find Lipo packs?

I cannot recommend any supplier, they are only available used from your local junkyard and are only a good fit for someone who wants to tinker and recycle something from the wrecker.

I mentioned it because the local wreckers when they get a hyrbrid (they usually avoid them) they want the battery gone asap and sometimes just about give it away, even considering these are 5.5-6.5ahr 144-300v packs.

[Ryland]

a battery management system is needed with lithium because they are not as forgiving, a BMS that can cut power to the main contactor as well s cutting power to the charger is ideal, otherwise you risk damage.

[TurnNBurn]

Originally Posted by rmay635703

I cannot recommend any supplier, they are only available used from your local junkyard and are only a good fit for someone who wants to tinker and recycle something from the wrecker.

I mentioned it because the local wreckers when they get a hyrbrid (they usually avoid them) they want the battery gone asap and sometimes just about give it away, even considering these are 5.5-6.5ahr 144-300v packs.

Cool. I'm going to check out a few and keep my eyes peeled. Why do they try and get rid of them ASAP? Is it an environmental issue keeping them around?

-edit-

I've got a few leads to some auto shops. I have a few questions. Am I looking for just the batteries or do these setups come with a BMS? i'm thinking about snagging the chargers as well if I can get a hold of some, but I just want to know what I'm looking out for to include in my setup.