Battery Choice.

[tomtag]

I recently converted an MTB & at the time did not realise how important battery selection was. After reading more & more on here I am now interested to find out whether I have made a good choice that matches the motor & controller or not. I have a MXUS XF08C rear hub motor with a KT 36V 250W 6Mosfets 15A Brushless DC Sine Wave Controller. The battery I bought was a 11.6Ah 36V bottle type battery from Yosepower. I believe it contains Samsung 29E cells. It is no longer on their site so cannot post a link. I would be really interested to know if this is a good battery & whether it allows me to see the full potential of the motor if anyone would be kind enough to comment?
Thanks.

 

[Alan Quay]

There's no reason why that won't work with a 15a controller. If it were too small it would probably cut out on low voltage, so you'd know about it.

I assume its has 40 cells, in a 10s4p configuration? (ie, about 2k in weight)

 

[WheezyRider]

I recently converted an MTB & at the time did not realise how important battery selection was. After reading more & more on here I am now interested to find out whether I have made a good choice that matches the motor & controller or not. I have a MXUS XF08C rear hub motor with a KT 36V 250W 6Mosfets 15A Brushless DC Sine Wave Controller. The battery I bought was a 11.6Ah 36V bottle type battery from Yosepower. I believe it contains Samsung 29E cells. It is no longer on their site so cannot post a link. I would be really interested to know if this is a good battery & whether it allows me to see the full potential of the motor if anyone would be kind enough to comment?
Thanks.

Sounds fine, I would expect 20 to 30 mile range depending on use and conditions for that size pack. I had an issue with one Yose Power battery where the solder joint to the main fuse failed. But I think generally they are ok and the Samsung cell bottle type is their more premium product.

 

[Nealh]

29E cells are very good as long as they aren't stressed by current demand 10s 4p should be good for a 15a controller, if you can find a 10s 5p/14.5ah 29E battery it would be even better. I have two 29E 14.5ah batteries now well in to their sixth year and both return 30 - 40 miles in PAS 1 or 2, early in their life I abused them with current and 25+ mph speed and they took a hit but still are reliable and only cut out/sag under throttle use after I have put about 15 miles on them.

 

[tomtag]

Morning All, Thanks for the responses. It sounds as though I have chosen a battery that is suitable for the motor which is good news. I just need to look after it well now to give as long a life as possible.
I try to set off with low assistance or by dragging the brake slightly to cut out the motor until I'm moving & also don't use the throttle at all so that will hopefully avoid any high current draws. I copied the controller spec above from the advert for the kit, but I have a feeling it was marked 7/10A on the actual controller. I will open the housing again and have a look. I also haven't had max speed setting above 16.5 mph so hopefully that allows some protection as well.
Nealh is there a reason why a 10s 5P battery are an ideal option? Is it due to the fact they can allow a higher current draw? (ie. 5 x continuous current rating of individual cell -2.75A in place of 4x). So would be less vunerable to damage when setting off etc?

 

[tomtag]

And AlanQuay, to respond to your question, I believe it is a 10S 4P configuration, but am unable to get it off the bike at the moment to check weight. It is in a black steel bottle shape housing that Yosepower are still using for some of their other batteries. I think the weight of it on the initial advert was 2.7 or 2.9kg with housing which seems about right?

 

[Nealh]

No need to drag the brake setting off just use PAS 1 or 2 level which will draw minimal current, speed wise you will be fine up to about 20mph.
Yes more cells in parallel lessens the current draw from each individual cell in the parallel connection, 5 cells rather then 4 means each one is 20% less stressed.

 

[WheezyRider]

Morning All, Thanks for the responses. It sounds as though I have chosen a battery that is suitable for the motor which is good news. I just need to look after it well now to give as long a life as possible.
I try to set off with low assistance or by dragging the brake slightly to cut out the motor until I'm moving & also don't use the throttle at all so that will hopefully avoid any high current draws. I copied the controller spec above from the advert for the kit, but I have a feeling it was marked 7/10A on the actual controller. I will open the housing again and have a look. I also haven't had max speed setting above 16.5 mph so hopefully that allows some protection as well.
Nealh is there a reason why a 10s 5P battery are an ideal option? Is it due to the fact they can allow a higher current draw? (ie. 5 x continuous current rating of individual cell -2.75A in place of 4x). So would be less vunerable to damage when setting off etc?

"15A" Controllers are usually marked as about 7 Amps continuous and 15 Amps peak. As Nealh says, don't worry too much about starting off with the brake applied, just use a lower assist level. You can find a good review of your cells here:

Test of Samsung INR18650-29E 2900mAh (Blue)

It says the normal max continuous current draw is 2.75A/cell, so 11Amps for packs with 4 cells in parallel. For peak use, it's 8.25Amps/cell, so 33Amps peak for your pack (although the BMS/internal fuse may trip things before you reached that level). It's unlikely that you'll strain the pack too much in everyday use. I think the only time might be if you are going up a very long steep hill at full assist, drawing maximum amps. But even then, if you look at the link, the guy did discharge cycles at 7Amps down to 2.8V and nothing catastrophic happened.

To maximise pack life, try to avoid deep discharges as much as possible, don't leave the pack in the garden shed in freezing weather, don't charge below 5 Deg C if possible, and certainly not below freezing.

NB, for safety, if charging in the house, never leave Li-ion cells charging unattended and especially not overnight.

 

[Nealh]

The cells can deliver 8.25a but don't expect good use out of them, they will suffer damage as I found out before I really understood cell specs.
The 1c rating is usually the safe current draw for a low power cell, the C rating is 1x the minimum capacity stated, as you go up the scale 10a, 20a cells etc have a higher C rating up to 8x C. The more the C rate drawn the lower the cycle capacity over lifespan of a cell.

 

[WheezyRider]

The cells can deliver 8.25a but don't expect good use out of them, they will suffer damage as I found out before I really understood cell specs.
The 1c rating is usually the safe current draw for a low power cell, the C rating is 1x the minimum capacity stated, as you go up the scale 10a, 20a cells etc have a higher C rating up to 8x C. The more the C rate drawn the lower the cycle capacity over lifespan of a cell.

Absolutely. And with a 15A controller, it should keep things to 3.75A per cell, and it should only be drawing that for long periods if going up a long steep hill (or cycling into a gale!).

Nealh, what is your advice for charging to maximise battery life? You don't want them being deeply discharged, so you want to recharge whenever you can, but you also don't want to be charging them back up to 4.2V/cell every day. Some people say you should only go as far as 4.1V/cell for maximum pack life. What do you do practically to achieve that?

I've wondered about using an Arduino to cut charging when the pack gets to 4.1V/cell, then have it set so that say after every 30 charges it does an equalisation balance charge to the full 4.2V/cell. Have you got a set up like that?

 

[Nealh]

I now simply charge to 41v for my 36v batteries and 53.3 for 48v , I adjust the voltage pot to 41v and that's it. So far this year I haven't seen any change in battery use with mileage or cut outs so cells are relatively remaining well balanced, my main use bike uses a simple KT lcd with basic functions and a four segment battery bar the bar remain solid and loses a bar every 25% of battery reduction no dancing up and down unless I use throttle where it will drop a couple before rebounding. If I notice a change then I will simply use the charger which is set for 42v to balance charge.
The top 0.1v accounts for about 2% of total battery capacity/range, I'm not seeing any detriment to range as it is usually spent by 1.5 - 2 km of use it holds little in the way of mah as does going below 3.3v.

Here is the discharge range for 5300mah 13a rated Boston Swing cell using a continuous 1a discharge load.
4.2v - 4.1v 100mah.
4.1v - 4.0v 450mah.
4.0v - 3.9v 400mah.
3.9v - 3.8v 500mah.
3.8v - 3.7v 525mah.
3.7v - 3.6v 700mah.
3.6v - 3.5v 11000mah.
3.5v - 3.4v 650mah.
3.4v - 3.3v 380mah.
3.3v - 3.2v 130mah.
3.2v - 3.1v 80mah.
3.1v - 3.0v 40mah.

The charging regime isn't for everyone but it is a simple practice to carry out.
Before every charge I always check charger output, time taken 5 seconds.

 

[WheezyRider]

I now simply charge to 41v for my 36v batteries and 53.3 for 48v , I adjust the voltage pot to 41v and that's it. So far this year I haven't seen any change in battery use with mileage or cut outs so cells are relatively remaining well balanced, my main use bike uses a simple KT lcd with basic functions and a four segment battery bar the bar remain solid and loses a bar every 25% of battery reduction no dancing up and down unless I use throttle where it will drop a couple before rebounding. If I notice a change then I will simply use the charger which is set for 42v to balance charge.
The top 0.1v accounts for about 2% of total battery capacity/range, I'm not seeing any detriment to range as it is usually spent by 1.5 - 2 km of use it holds little in the way of mah as does going below 3.3v.

Here is the discharge range for 5300mah 13a rated Boston Swing cell using a continuous 1a discharge load.
4.2v - 4.1v 100mah.
4.1v - 4.0v 450mah.
4.0v - 3.9v 400mah.
3.9v - 3.8v 500mah.
3.8v - 3.7v 525mah.
3.7v - 3.6v 700mah.
3.6v - 3.5v 11000mah.
3.5v - 3.4v 650mah.
3.4v - 3.3v 380mah.
3.3v - 3.2v 130mah.
3.2v - 3.1v 80mah.
3.1v - 3.0v 40mah.

The charging regime isn't for everyone but it is a simple practice to carry out.
Before every charge I always check charger output, time take 5 seconds.

Nice. Do you have a specialist charger, or did you open up a standard charger and find the voltage out adjust pot?

 

[Nealh]

Basic Sans charger.

Basic Sans charger mods/adjustments.

Over the years I have acquired 4-5 Sans type chargers for 36v and have a pair set up for 41.2v charging (not balance), every 6- 10 charges I fully balance with a standard 42v charge to ward off an imbalance that may occur. The Sans will charge 10 -12s as it has a voltage adjustment range of...

www.pedelecs.co.uk

 

[WheezyRider]

Basic Sans charger.

Basic Sans charger mods/adjustments.

Over the years I have acquired 4-5 Sans type chargers for 36v and have a pair set up for 41.2v charging (not balance), every 6- 10 charges I fully balance with a standard 42v charge to ward off an imbalance that may occur. The Sans will charge 10 -12s as it has a voltage adjustment range of...

www.pedelecs.co.uk

Thanks for the link! I took apart a charger last year, hoping to find a pot inside as it was 42V output, but it didn't have one. I had thought about putting a couple of diodes in series with the output to drop the voltage down to 41V and set up a switch so I could swap between 41V and 42V. However, I've looked at my Yose Power chargers and they are SANS, so hopefully I will be able to find a pot inside them to adjust output. Unfortunately, they don't seem to have screws like yours to get them apart, so I might have to 3D print a new case afterwards!