Electric Bikes - motor cuts out with quick throttle...

Does anyone know what could be causing this problem? I have a 500 watt hub motor, 72 v clyte controller, and 48v 20ah lifepo4 battery. The kit works great 90% of the time. The problem is that when I twist the throttle moderately quickly to get going or while I'm on a hill the power seems to cut out. My cycle analyst flickers and then shuts and then the throttle is unresponsive. I have to unplug the battery-controller connection, replug it in, and then everything is fine again until I give too quick a throttle again and it cuts out. Any suggestions on how to fix this issue.

Sounds like a Bad BMS.

Cycle Analyst should record the peak current for you, even though it gets shutdown. I'd reset the CA, make the system shutdown, restart it and check peak current to see if you are exceeding the battery's maximum rated current. If the current draw is within spec, you may have a bad BMS as brownj24 said. If not, you have the choice to bypass the BMS to get more peak current, I'm not sure what the consequences of that is, or get a battery with more peak current allowance.

Or you may be hitting the low voltage cut off of the controller at peak current. This could happen if you have one or a few bad cells.

Good point gmouchawar, Cycle Analyst should also record minimum voltage which would help with that determination.

Cycle analyst shows min Voltage of 17.6 before it cuts out.

That is way too low for a 48V pack. Something is drastically wrong.

This is the lowest reading captured by the cycle analyst just before the power cuts out from the battery/BMS. Is it possible that the cycle analyst is reading the quickly declining voltage immediately after the BMS shuts off the battery (which happens when I apply a quick throttle)? So, it would actually be a reading after the the BMS has been engaged as opposed to prior? I don't know, just a thought. How do I know for certain if it's the battery or the BMS? I have been quite happy with the battery other than this one issue. I get a consistent 40 km on one charge with a 300 lb load (me 240, battery 25, motor 20, bike 15). Should I be getting more?? Not sure what to think about this battery.

You raise a very good question about what the CA is recording when it's in the process of losing it's own power supply.

Does anyone know what voltage the CA needs? It may not be a bad idea to build a dedicated power supply form the CA using NiCads or any cheap batteries, this was you'd know for sure it's not falling victim to the shutdown.

The following is a msg I got from the guy who sold me the battery on ebay...

"Hi friend
Can I suggest you a method?
The technical told me that the BMS limit the current early...Can you see the picture? There are 10 resistance wires, two parts..You can make one part to short circuit, using solder wires...Can you make this?
The technical told that the BMS is OK, but the design is not so good,so it make output current small...
Looking forward to hearing from you.."


I've never soldered anything and I just want to confirm that he's asking me to solder together, in pairs, 4 of the 10 resistance wires on the BMS. I've attached a picture. Maybe some slightly more detailed directions if any of you know exactly what he's talking about. Thanks!

hmm shortening the shunts with solder will also change the max amps drawn from the battery.
i would test the voltage on each cell before moding.

bypassing the protecion for the cells is a last resort.

cheers

If you go the shunt bypass route, I'd do it with some alligator clips and jumper wire to see if that really solves it before I'd start soldering. My 2 cents.

It sounds like the vendor is instructing you to bypass one of the two banks of shunts. I've never pulled one of those things apart or seen a circuit diagram so it's hard to say. May be a good idea to sketch something out showing what you are planning to do, scan and email it to him for clarification.

I have the same problem. I think it has to do with the C rating on many ping ping battery's being <1. Thus when you request too much power at once from the battery, the whole bike shuts down to prevent the battery from being damaged. I believe the only way to fix it is to get a device to restrict the amount of power that the motor can drain at one time.

Yeah,

Misslexi is right. He's asking me two bypass one of the two banks of shunts shown in the picture. I've attached another picture of a clarifying sketch he sent me and it seems obvious that's what he's talking about.

Good suggestion regarding the alligator clips. I will definitely do that. Just to be sure, I need to alligator clip each of the bars in one of the banks of shunts in order to bypass that whole bank, right?

I was thinking I could bypass a couple bars at a time in one of the banks until I found an optimal current flow.

The important question I have is when do I risk doing damage to the battery? Right now, although it's really annoying, I can put up with the problem. The last thing I want to do at this point is ruin the battery or any other component.

Could one or more of you knowledgeable folks lay out the things I should be aware of when trying this solution? THanks!

if you do it avoid steep hills. look for swelling of a cell and overheating. just keep a eye on the pack
untill you fully test it.

Good suggestion regarding the alligator clips. I will definitely do that. Just to be sure, I need to alligator clip each of the bars in one of the banks of shunts in order to bypass that whole bank, right?

Lets say you have 5 shunt wires he's instructing you to solder, you can accomplish this electrically with 4 jumpers; 1 to 2, 2 to 3, 3 to 4, and 4 to 5.

I don't know enough about the circuit to understand why the recommendation to bridge the shunt. The only way I can imagine this altering things electrically is if the 5 shunts are connected in series, something like end A of 1 connected to circuit, end B of 1 connected to end A of 2...end B of 5 connected to circuit. This arrangement would have some finite resistance which when bridged would be at, or close, to zero resistance. This would allow more current to flow though the shunt. Since I have no idea what the function of the shunt is, I can't speculate as to what the outcome of the experiment will be.

Keep us posted.

I'll give it a try and let you guys know what happens. Thanks for posting.