Parallel Batteries

Benjahmin

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Nov 10, 2014
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#21
Yeh, it was an oversight, normally quite careful. Good job we're only talking 0.2v difference.
 
D

Deleted member 4366

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#22
Yes, that's why you mustn't charge in parallel. The BMS of the second one cannot switch off the charging when a cell reaches the maximum 4.2v. Basically, the second battery will continue charging until a cell in the first one reaches 4.2v.
 

Benjahmin

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Nov 10, 2014
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#23
So, a year on and the system works well. However the Ezee battery (that I suspect is pouch cells) now only charges up to 41.1v. Seems to hold the charge fine. So I'm wondering, at what stage do you call it a day with a battery? Couldn't say what it's range is now because I've been using it in parallel since the OP here. The max voltage difference is getting close to the 0.5v differential that I have in mind as a safe limit. What do you reckon?
The Insat battery (Boston power cells) always has charged to 41.5.
 

anotherkiwi

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Jan 26, 2015
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#24
So, a year on and the system works well. However the Ezee battery (that I suspect is pouch cells) now only charges up to 41.1v. Seems to hold the charge fine. So I'm wondering, at what stage do you call it a day with a battery? Couldn't say what it's range is now because I've been using it in parallel since the OP here. The max voltage difference is getting close to the 0.5v differential that I have in mind as a safe limit. What do you reckon?
The Insat battery (Boston power cells) always has charged to 41.5.
I would say the day it only charges to 41v it has had it's time. My bottle battery only charges to about 41.2v these days so I only use it in parallel with 10 Ah of LiPo and since I started doing that it is pretty stable.
 

Nealh

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Aug 7, 2014
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#25
Once the voltage starts becoming different then best only paralleling once out on a ride and the Boston one is at the lower pack voltage level.

Problem with an older tired battery is the better one will suffer a little as it has to make up for the lesser ones shortfalls. The Ezee pouch cells probably have high IR and may be a bit puffed if any packing pressure is released. Time to call it a day is when you determine if the older parallel pack actually still gives you any advantage.

Run locally with just the Ezee battery and see how it performs, if it sags badly and cuts out in under ten miles then might be best to call it a day, as mentioned above any battery in P that is a bad performer will be asking the other one to compensate which may cause damage to it. If one sags badly the other will try and compensate each time by large flows of equalisation voltage and a lot or most may be wasted as heat.
 

Benjahmin

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Nov 10, 2014
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#26
Yup, I'll have to give the Ezee a run on it's own and see what the local hills do to it. Kinda want a new battery but I think I have a shot of Yorkshire genetic ( that's like a scottish one but with the warm streak of generosity removed :D).
 

Benjahmin

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Nov 10, 2014
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#27
Just done the local shopping run, a faily hilly 8+ miles, on the Ezee battery alone. Start voltage was 41.1. On the way back at around 6 miles there's a 3/4 mile hill with about 400yds of it at around 1/6 0r 5. This bought the battery indicator down to 1/5. It recovered to 4/5 going down the other side but was at 2/5 by the time I'd done the gentle climb to home. It recovered to a resting 4/5 38.2v.
Given the amount of hilly miles you have to do to get anywhere around here, plus my big Ezee motor, plus the fact that the battery I run in parallel is actually for our guest bike, I'm guessing that the time may have come. This battery was bought in November 2014, cells unknown, always been kept inside. It's been punished with some pretty long and sreep climbs fairly regularly and, in total (including time paralleled) it's done getting on for 8000miles. Seems fair to me. I'll have to get some pictures and measurements ready for Jimmy.
 

Nealh

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Aug 7, 2014
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#28
What's the controller rating on your Ezee ?

38.2v is about 50% considering battery is missing 5-8% top charge, advantage of paralleling is that not only does ah/wh become accumulative but also the battery amps. Even with a poorly/ageing battery cell amp draw is lessened, the only factor unknown is how much voltage flow there is between the two packs when in use if the older one sags badly.
 

Benjahmin

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Nov 10, 2014
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#29
Well the spec sheet says 54v max 30v min, 20A limit. Never looked before, that's interesting. In practice I use it fairly exclusively in setting 2/5. Don't know if the setting are current limiting or speed, suspect the latter.
I think the main thing here is that the Bga battery was built for and can be used on another bike. It gets used when my daughter or some other guest visits. If I were to do that and use the Ezee battery solo in it's present condition, I don't think I'm going to get far. Again, spec sheet says it's 18650 Samsung cells, I'd always assumed they were pouch cells.
So thanks for the question Neal, you've made me take another look at the spec sheet with the greater understanding of being around here for a while.

There is an oddity with this kit that I've never got to the bottom off.
The only time I hear the motor turn off is when brake lever is pulled or I stop peddalling. So, if I am going down hill at say 25 or 30 mph and continue to peddle the motor can be heard rotating, if I stop peddalling I can hear it stop. It never reaches a cut out speed. I wonder if it actually relies on magnetic saturation for it's speed limit. When on the work stand pas 5 or throttle gives a cateye computer reading of 19mph. On a flat road, with me peddalling, I have achieved this speed and the motor just continues. Not a bother, just odd.
 

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