Low voltage cutoff and sag

[mrzed]

Hi all,

I am running a 9C kit from eBikes.ca with a 36v/8aH NiCad. The site states a recommended 1v per cell as the low voltage cutoff to prevent cell damage, that would be 30v.

With the cycle analyst showing around 6aH discharge, the pack runs around 32-33v with no load. Running level, sags down a little over 30, but for acceleration and especially up steeper hills, it can readily sag below 28 for short periods.

Should I:

1. Set the LVC on the cycle analyst? I would expect this would cut off power when I often want it and so I have not yet gone this route
2. Carefully feather the throttle on hills to try keeping it as close to 30 as possible (what I am doing now)
3. Not worry about sag and just not let the pack discharge below 30v at rest

 

[dnmun]

you should charge up the battery if it is low, no need to run it into the ground. but your controller should already be cutting out if you drop below 30.5V.

if it drops to 27-28 under load, i think you would still be safe, but try to charge before then.

30V in standby is a good number to keep above.

 

[dogman dan]

I have two 24v nicads from ebike ca that I'm running series connected (48v) with a 5304. I try very hard to limit full throttle riding to keep from toasting the batteries, but when I bought them, and used them as I first intended, paralelled for 24v 16 ah, I had no worries, no noticable sag, and never got the pack hot no matter how much I hammered the throttle. Get a second nicad pack or some sla's and paralell them, and your problem will vanish. It'll be heavy, but worth it. For now, the best way is to pedal a bit more and use the motor more in an assist manner.

 

[mrzed]

I always pedal - but i do use full throttle on flats and hills for the most part - intermittent though as the ride is quite variable. They get a bit hot, but the longest leg of my ride is 15 minutes, and I'm in a temperate climate - rarely over 20c.

I'm draining them about 75% because that's my commute - but I do charge them every day. My initial plan was to keep this pack for 2-3 years, as it is adequate for my needs, then upgrade to a 48v LiFePO4 later when they are cheaper. The torque difference in the motor is quite notable when it is fresh off the charger at 40v. I just can't justify the cost when the current setup works just fine for pulling the kid to daycare.