New 16-cell Battery Management System (BMS)

[fechter]

That should be no problem. You would only need to change one resistor on each channel. As long as you know ahead of time what voltage you want, the proper resistors can be used.

There should also be some selection of low voltage cutoff point depending on which TC54 versions is used. Again, you would need to know this ahead of time to make a part substitution.

What kind of cells take 4.2v?

 

[commanda]

What kind of cells take 4.2v?

ThunderSky.

Amanda

 

[jeffkay]

And Kinion. Also weird lipo packs...

 

[jeffkay]

Richard or Gary, I forgot, is there any way to connect to the bms for end of charge? I want to turn off my PS (has a logic line for that) when it is done. If no, I guess it would be easy to tap the LED, but we have yet to see the final schematic...
Jeff K.

 

[docnjoj]

Hey Gary! Non expert alert!!! Can I use a regular 36 volt W/E charger to charge Lifebutts? This assumes using your BMS!
otherDoc

 

[fechter]

Richard or Gary, I forgot, is there any way to connect to the bms for end of charge? I want to turn off my PS (has a logic line for that) when it is done. If no, I guess it would be easy to tap the LED, but we have yet to see the final schematic...
Jeff K.

No, that feature is not part of the new circuit. Once all the cells take on as much charge as they can handle, they will just float at the set point voltage. If the charger is turned off, the batteries will be drained slightly by the charge control circuit and possibly the charger. It might be possible to use some kind of timer switch to terminate the charge.

With LiFePO4 batteries, they should be able to float for quite a while without damage. This would not be good for Lipo or Li-Co cells.

A standard SLA charger can be used if it can supply enough voltage for the number of cells.
In most cases, it might be a bit on the low side and need tweaking or used for a different number of cells. A 36v SLA charger would probably be a few volts shy for what 10 cells would take.

 

[docnjoj]

Hey Richard! Thanks! Would this "few volts shy" effect have negative consequences to the batts, or could it result in longer lifespan for Lifebutts? I realize it wouold be undercharged and therefor less range!
otherDoc

 

[GGoodrum]

Richard or Gary, I forgot, is there any way to connect to the bms for end of charge? I want to turn off my PS (has a logic line for that) when it is done. If no, I guess it would be easy to tap the LED, but we have yet to see the final schematic...
Jeff K.

I'm not sure about an end-of-charge signal yet. We're still testing what happens with different charge voltages, etc.

-- Gary

 

[GGoodrum]

Hey Richard! Thanks! Would this "few volts shy" effect have negative consequences to the batts, or could it result in longer lifespan for Lifebutts? I realize it wouold be undercharged and therefor less range!
otherDoc

Actually, most 36V SLA chargers have a CC/CV cutoff around 44-45V, which is 3.66-3.75V per cell, for a 12-cell LiFePO4 pack. We're using 1% resistors on each channel's input divider, which means the cutoff can range between about 3.65-3.70V. The charger just needs to be just higher than the sum of the shunt cutoff voltages. An easy way to test this to simply connect the charger to the BMS board, without the cells connected. If the charger is putting out enough voltage, all the orange LEDs will be on.

-- Gary

 

[docnjoj]

Thanks Gary! Good Deal! If the little lights dont light...............? In other words, is undercharging bad??????
otherDoc

 

[sharkmobil]

Not that bad. AFAIK a little undercharge actually prolongs the life of the batteries.

 

[julesa]

I'm new here, ... does anybody here have any idea if my contoller COULD handle the 16 cells, which I would prefer anyway. I ride this to work each day, and I'm often running late. Any extra speed would be nice.
dc

Hello Dave.. yes.. your crystalyte controller will take a 48v pack .. charged up to 56v no problem .. ( well. sometimes they blow up.. but i've done this many..many times over with 16 cells without any issues.. ) :wink:

Hi Ypedal, have you tried this with your ezee controller? I was thinking I'd get one of those and run at with a 16 cell LiFePo4 pack.

 

[PJD]

Amanda,

Are you referring to Thundersky LFP cells?

There seems to be a rather large consensus that you should charge these cells to about 3.7 volts per cell, as in other LiFePO4 cells. Do NOT charge them to the "factory recommended" 4.25 volts per cell. Most people believe the factory recommendation for charging the LFP cells to 4.25 volts was erroneously carried over from their lithium cells. (LiCoO2, LiMnO2) It seems odd that most people recommend defying the factories own recommendation, but such sloppiness in specifications, product testing, and QC seems to be unfortunately typical of Chinese firms.

But, if you have newer data that suggests that 4.2 volts is the correct charging voltage, I'd like to hear it!

Paul D.

 

[PJD]

An easy way to test this to simply connect the charger to the BMS board, without the cells connected. If the charger is putting out enough voltage, all the orange LEDs will be on.

That won't work on a lot of chargers - the charger needs to detect a certain minimum voltage or it doesn't turn on.

 

[commanda]

Amanda,

Are you referring to Thundersky LFP cells?

There seems to be a rather large consensus that you should charge these cells to about 3.7 volts per cell, as in other LiFePO4 cells. Do NOT charge them to the "factory recommended" 4.25 volts per cell. Most people believe the factory recommendation for charging the LFP cells to 4.25 volts was erroneously carried over from their lithium cells. (LiCoO2, LiMnO2) It seems odd that most people recommend defying the factories own recommendation, but such sloppiness in specifications, product testing, and QC seems to be unfortunately typical of Chinese firms.

But, if you have newer data that suggests that 4.2 volts is the correct charging voltage, I'd like to hear it!

Paul D.

I was just going on Thundersky's published data. I'll rethink that and set my BMS to 3.7 and see what capacity I get.

Should add I've ordered and paid for the cells, but don't expect to see them for several months yet.

Amanda

 

[fechter]

An easy way to test this to simply connect the charger to the BMS board, without the cells connected. If the charger is putting out enough voltage, all the orange LEDs will be on.

That won't work on a lot of chargers - the charger needs to detect a certain minimum voltage or it doesn't turn on.

This will work with a Soniel charger, but yes, you may need to "jump start" the charger by applying voltage from the battery long enough to get it going if it has that kind of battery disconnect safety feature.

 

[PJD]

This will work with a Soniel charger, but yes, you may need to "jump start" the charger by applying voltage from the battery long enough to get it going if it has that kind of battery disconnect safety feature.

So, will this be needed to use your board? Should I plan on adding a "start charge" switch that momentarily applies battery pack voltage to the charger "+" and "-" connections?

 

[fechter]

I was referring only to testing the charger voltage. In normal operation the battery would be connected and would feed voltage to the charger.

 

[GGoodrum]

This will work with a Soniel charger, but yes, you may need to "jump start" the charger by applying voltage from the battery long enough to get it going if it has that kind of battery disconnect safety feature.

So, will this be needed to use your board? Should I plan on adding a "start charge" switch that momentarily applies battery pack voltage to the charger "+" and "-" connections?

No, this only apllies to my comment about testing the board without the cells connected, to see if the charger puts out enough voltage to be a bit higher than the sum of the shunt voltages. Normally, the board would be connected to the cells all the time.

 

[shinyballs]

Gary,

Also what are the dimensions of the the TP201's (and the LVC). Maybe you can add this info the your website. Thanks!

I also have the same quesion, so I know where to mount before building my battery casing

 

[fechter]

I split this topic and started a new one. The discussion continues in the new thread:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416