First Electric Motorcycle Conversion Advice (1974 Honda CB360)

[harrisonpatm]

Electrically, that all looks like it will work as intended, to me at least.

One thing I am still confused on is where the "Trig -" wire from the contactor should go. Is where I have it in the diagram correct, or should I have it spliced into the "B+" wire.

You have it draw correctly, Trig - goes to B-, not B+.

What's the difference between the two rockers? Just color?

If you're going with 1kohm precharge, keep in mind that depending on the controller's capacitors, it could take anywhere from 5-20 seconds for a decent precharge. Which is fine.

Also, if you're going with 1kohm, you can basically use "any" 1kohm resistor, not sure you need a $10 item. You already ordered, but here's 10 suitable resistors for $6.

 

[RealPolarBear]

What's the difference between the two rockers? Just color?

Yup, literally just color. In my mind this will help me differentiate between the two different functions: one enabling the precharge circuit, the other operating the contactor.

Also, if you're going with 1kohm, you can basically use "any" 1kohm resistor, not sure you need a $10 item. You already ordered, but here's 10 suitable resistors for $6.

Ha, that is fair. I figured I mind as well order it all from one place for simplicity.

 

[Dui ni shuo de dui]

Alright so I've been working on incorporating everyone's feedback and I believe I have come up with a pre-charge contactor circuit that will work for me. Parts have been ordered.

For those curious about the components, they are as follows:
72V Coil Contactor
72V SPST Switch
72V SPST Switch
250A Fuse
1k Precharge Resistor
400V 3A Suppression Diodes

View attachment 351606

One thing I am still confused on is where the "Trig -" wire from the contactor should go. Is where I have it in the diagram correct, or should I have it spliced into the "B+" wire?

For me there's a mistake at the flyback diode system.
If you really want to use two diodes, in my opinion one should be a zener diode. I don't think it makes sense to use two regular diodes as you will be blocking the current in both direction, which essentially seems to me like an open circuit. Basically it's like having nothing at all.

I wouldn't bother with overcomplicating this thing and simply go with the traditional single diode system, as it's working absolutely fine.
But I'm not an electrical engineer, it's just my opinion.

So basically you plan on having 3 switches just to turn on the bike (not mentioning another physical or virtual switch to turn on the BMS so that's 4 in total). That sounds rather complicated to me but it's not my machine so if that's what you like then no problem. Otherwise you could simplify a bit by merging the precharge switch and the coil switch into one single switch. For example you could wire it to a three position switch, so that the right position if off, the middle position activates the precharge and left position activates the coil. Since you have to pass through the middle to go from OFF to ON then it would precharge just before switching ON no matter what.

Ah, also I would add a fuse before the coil, to protect the wiring system in case there's anything wrong with the coil.

 

[RealPolarBear]

Hi all! It has been awhile since I've been able to work on my e-motorcycle project but I finally was able to wire up the contactor and precharge circuit. I ended up following this diagram:



Despite the excitement of seeing everything fire up, I am facing a problem where even when I switch the contactor (red switch), and precharge circuit (black switch) off power is still getting to my motor controller, even though I hear a click. It is the weirdest thing and I cannot wrap my head around it. I am not sure if the contacts welded somehow but I will definitely be isolating the contactor and testing it for continuity later. If this is the case, I don't know how it would have happened. I feel like the circuit is pretty simple and I haven't even had the chance to put over 10A through the circuit. Right now it reads 84V. I am wondering if there is anything I should lookout for and test here.

Here is a link to the contactor.

 

[harrisonpatm]

Hi all! It has been awhile since I've been able to work on my e-motorcycle project but I finally was able to wire up the contactor and precharge circuit. I ended up following this diagram:

View attachment 359264

Despite the excitement of seeing everything fire up, I am facing a problem where even when I switch the contactor (red switch), and precharge circuit (black switch) off power is still getting to my motor controller, even though I hear a click. It is the weirdest thing and I cannot wrap my head around it. I am not sure if the contacts welded somehow but I will definitely be isolating the contactor and testing it for continuity later. If this is the case, I don't know how it would have happened. I feel like the circuit is pretty simple and I haven't even had the chance to put over 10A through the circuit. Right now it reads 84V. I am wondering if there is anything I should lookout for and test here.

Here is a link to the contactor.

While it's possible that the contacts on the (black) precharge switch have welded shut, it's unlikely with that resistor in line. If they did weld shut, then the resistor is always on, and the controller technically does always have power.

How are you determining that the controller is still getting power? You can turn it on and it holds power and voltage? Because it's possible that the capacitors are holding the 84v charge from the batteries after turning it on to test the contactor. And if they're big enough, they are possibly holding said charge long enough to keep the controller on for awhile. I'm assuming that you don't have the motor hooked up or anything yet?

 

[RealPolarBear]

I hadn't considered the capacitors in the controller. I have a little battery monitor at the connection to my motor controller. It reads 84v and I can turn the keyswitch for my controller and still have lights and motor power. It's the weirdest thing.

 

[harrisonpatm]

Simplest check is to probe the two main contacts of the contactor with a multimeter set to continuity function. If you read a short circuit regardless of the contactor being on or off, then yeah, bad contactor.

 

[harrisonpatm]

You can use the same method to check whether the contacts of the black precharge switch have welded shut

 

[RealPolarBear]

Just tested for continuity across the contactor and unfortunately it shorted when the switch was both on and off. Both switches themselves only shorted in the on position. So I guess the contacts are welded together; there goes $140 . I don't know how my circuit would've possibly welded the contactor as there's a 250A fuse and I was getting readings of 84V. Further, I haven't applied a load of more than 5A off the battery to test the motor. The contactor is rated for 500A continuous and 900V! I think I'm going to be out of luck trying to get a refund or replacement of any sort. Can anyone recommend a contactor which might work better for me?

 

[harrisonpatm]

You just bought it, right? Send it back. Send a picture of your multimeter reading a short in both open and closed positions.

 

[RealPolarBear]

Sadly I bought it at the end of may and just not got it unboxed and tested. To my avail... it doesn't work. The customer support of the website I bought it from said that, "these devices can be destroyed in seconds," which is absolutely baffling to me. They essentially believe the fault is on my end. I don't know how I could have a chance at destroying it without first blowing any fuses. As much as I wish I could, I doubt I'll get my money back. Of course, I will still try.

 

[harrisonpatm]

You also mention that you hear a click. That kinda implies that they're not fully welded together; there wouldn't be a sound if nothing was moving.

Can you take a picture of how it's actually wired up?

 

[RealPolarBear]

That's what I was thinking too but I just can't explain the full continuity, regardless of the switch being on or off. I attached the best picture I could and a video of the switch having an audible effect on the contactor without turning off the power AT ALL. The battery monitor is monitoring the circuit after the contactor and I am still able to fully power lights and motor. Let me know if there is anything more I can provide to help.

 

[harrisonpatm]

That's what I was thinking too but I just can't explain the full continuity, regardless of the switch being on or off. I attached the best picture I could and a video of the switch having an audible effect on the contactor without turning off the power AT ALL. The battery monitor is monitoring the circuit after the contactor and I am still able to fully power lights and motor. Let me know if there is anything more I can provide to help.

View attachment 359279

You did the multimeter continuity reading on the contactor like the picture above?

If so. Disconnect everything from the contactor completely. Don't power the coils, then do a multimeter continuity test. Shorted still? Let's see if its an actual broken contactor

 

[RealPolarBear]

I tried disconnecting everything like you stead still to no avail. Are there any other tests I can run or is my contactor as good as dead. Here is a video of my test and the setup:

 

[harrisonpatm]

Yeah, it's a dud. Sorry.

 

[RealPolarBear]

I’m now taking recommendations for a new contactor if you have any tried and true winners.

 

[harrisonpatm]

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

For a 12v coil, you'd need a 72v-to-12v converter

Amazon.com

72v coil on that one

 

[RealPolarBear]

Ok, I just ordered the 72v coil from amazon that you recommended. You said you've worked with this one before, correct? Any issues or so far so good? We'll see if the same issue occurs as the last contactor ... hopefully not. In the meantime I get to start making the battery box

 

[Dui ni shuo de dui]

I guess this is one more actual experience of a contactor not being much more reliable than FETs
Reminded me of the beginning of the thread when we were having this discussion:

While it's unlikely for a BMS to have a serious failure, when the FET's fail, they can fail closed and are then unable to shutoff current. It's exceedingly unlikely for a contactor to fail closed, there's a spring pushing it towards open position. I suppose the only way for it to fail closed would be for the contacts to weld together. Which is why I recommended a contactor way way overrated for OP's use, at 900vdc and 500A capability, for his 72v/200A capable system. In addition, depending on exactly what parts were used to build a BMS, turning off output voltage may still cause some voltage to leak through. I'm not an electrical engineer, I just know that when I turn off my BMS via an app, I can still get low voltage readings off my battery terminals. I'd rather see 0V.

That's what I've always heard as well.
Then a friend of mine did the experiment himself, tried some automotive contactors. They all failed closed. It was a bitter disappointment as he wanted to install one to bypass the BMS mosfets in order to go over 600A battery.
BYD stuff, some big and beefy contactors intended for EVs, not the cheap stuff.

So I have to disagree on that now, even though I thought it was correct just a few years ago.

Again, I suggest you think again about whether adding a contactor actually worth the trouble. If they fail closed as we just saw then it means you can't trust it more than the BMS mosfets... so what's the point?
So far that is 140USD +15USd + some change for DCDC converters, for no added value.

 

[harrisonpatm]

Can't argue with that! OP gets to decide if it's worth it, maybe he'll go with just the BMS. I'll stick with contactors

 

[Tony01]

From the beginning of the topic I was going to say your batt is the weak point but not with a 72/75 molicel which you can charge at 1c or 75 amps which is right on the edge of the max a level 2 handle will give. Nice.

I would run no contactor and just leave everything plugged in. If the batt fails, there is nothing that will prevent your house burning down unless you keep your lithium outdoors at all times (as I do).

I would also run no BMS and simply balance manually from time to time. A large pack like that will only go out of balance .05v in 6 months even if you commute on it daily and even charge at 1c. I’d recommend also only using 3.5 to 4.1v per cell group, the cells will be healthier and you can beat on it mostly.

Less things to fail. A failed bms or contactor can scrap your battery too.

 

[j bjork]

If you get another contactor, make sure your pre charge works. When a contactor "fail closed" it usually means the contacts welded together because there was a high load when they were closing. (like charging capacitators)

 

[RealPolarBear]

Less things to fail. A failed bms or contactor can scrap your battery too.

This is a completely fair point. I figured having at least one more safety can’t hurt besides the key switch off the controller. That said if this next contactor suffers the same fate as the last one, I’ll just leave everything plugged in. I guess it’s good to figure all this out while it’s still laying on the floor not in the bike.

If you get another contactor, make sure your pre charge works. When a contactor "fail closed" it usually means the contacts welded together because there was a high load when they were closing. (like charging capacitators)

I’ll definitely be considering this w the new contactor, thank you!

 

[Dui ni shuo de dui]

I would also run no BMS and simply balance manuall it's ok for y from time to time. A large pack like that will only go out of balance .05v in 6 months even if you commute on it daily and even charge at 1c. I’d recommend also only using 3.5 to 4.1v per cell group, the cells will be healthier and you can beat on it mostly.

I'd say it's ok for a bike you're using only from time to time, but I wouldn't advise such a thing for a daily driver.
You just can't properly monitor the cells everyday, there will always be some external event to distract you. You won't check your cells after going to a party, or if you have some kind of emergency going on, or whatever.
Most of the time you also won't be there monitoring the end of the charge process, which is where most of the catastrophic failures happen. At least the BMS will monitor the cells drift and cut charge if something in your cells or your charger goes wrong. It will also beep at you if something is going out of the parameters you defined.
Manually doing the BMS job is technically doable, but thats a lot of hassle if you want to do it the proper way, plus it is very prone to human error. And you just can't do it in real time while riding.

The argument that a failed BMS can scrap your battery is not wrong, because everything can fail. But it is misleading because a failed user manual monitoring is far, far more likely to happen than a failed BMS. The best solution is to have both working together: the BMS as the primary safety source, and the user as a BMS controller.