A2b battery dead how to reverse charge?

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Aug 30, 2015
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Hi I bought an a2b with second battery from someone and it looks like it was sittig too long. The battery doesnt turn on and when connected to charger it stays green. With some tricks like turning charger off then on I can get it to flash yellow but after leaving overnight it flashes red.

I was wondering can I stick wires in the batterys output port, then solder to the charger pins to reverse charge it? Just wonder which pins get soldered to which on the charger?

I have a friend who probably has an rc type charger but didnt know if there were any hacks to try to get this battery running again. Thanks.

If this fails any suggestions for a battery thay would work well? 36 or 48 which is better. Looking for sort of simple way to get 10-20 more miles if needed. Thanks!
 
if it charges intially and then stops charging you have one cell that is pushed up to the HVC level and that turns off the charge. your only solution is to open the pack and find the high cells and drain the charge off of them so that the charger can continue to charge up the other cells until the pack can be balanced. if you charge now through the output you will overcharge the high cells and ruin the battery. as it is now it is recoverable perhaps but after overcharging the high cells it will be ruined.
 
why is the reason you want to do a "reverse charge"? for the battery is the same as putting a small load through the discharge or charge connectors.

There are some specifications to know. Battery chemistry? battery nominal Voltage? charger voltage? (rated and max measured) how much time stored with no charging? actual battery voltage? it is built-in charge and discharge separated ports?
 
If it's a genuine A2B pack , it will have decent quality cells (Sanyo normally) that seem to tolerate being ignored and left discharged for long periods. However, once it has drained to a "below safe voltage" (??) the BMS will prevent it being recharged as one or more cells will have dropped very low
But in order to get the pack back working again , you will have to crack it open and bypass the BMS whilst you look for the lowest cells to boost up individually to get the pack voltage back up to something like 25+ volts! when the BMS will let the charger work again.
You will need some skills, tools, a MMeter, and a lot of patience and care.
There is a site somewhere that shows how to crack that pack open ....I will try to link it for you.
EDIT:
Try this....http://grifftek.com/grifftek/Other_Fun_Projects_and_Hobbies/a2b_battery_packs/
 
i think he said it will charge initially but stops charging after a few minutes so that implies it is highly unbalanced right now. some cells are at the HVC and some are at the LVC so it cuts off on both ends.

if he will open the case and get access to the sense wires he could tell us what the voltages are on the cells. if he is still interested.
 
Hi All,

Firstly thank you so much, I am so thankful for your help.

My suspicion is that it was left too long and has dropped below 25v (based on nothing but gut feeling). I will follow guide to opening and will try to get some measurements from the cells which I will report here. So to clarify what is happening when I try to charge regularly, when I follow the guide and plug into bike first, then wall then flick switch the charger comes on and stays green like it has been plugged into a fully charged bike or a bike that wont take a charge. However I tried some messing around like unplugging and plugging right back in again or flicking the switch off then right back on again as it seemed to drain down the caps in the charger and when I tried these methods I could get the charger to go to a flashing yellow state, (I assumed this is some kind of trickle charge state perhaps), I left that over night a little sketched out in my office and it was flashing red the next morning, still wont charge or light up when I press the on button. So I think the best recourse is to open up the pack and use a multi meter to measure the voltages. If there is a cell or two that is too low can you recommend a charger that I can buy to get those cells back up to say 25v? Will try to get some numbers up here in the next day or so. Thanks!
 
we are trying to help you eliminate the guessing. plug the charger into the AC first, always. open the battery case enuff to get access to the BMS so you can measure the cell voltages.

measure the voltages on the BMS pcb at adjacent pins where the sense wire plugs into the BMS. use the 20V DC scale and measure each to .01V while charging. list the voltages here. post up pictures of the BMS too.
 
Ok thanks so much for the help. I'll try that this week and will post. Seems like a little work to get the case open but I am up for the challenge to potentially save me some cash. Any advise on where I put the mulitmeter prongs once the case is opened? I saw the pictures in the previous post but could use some direction on how to actually measure the voltage as in where the multi meter prongs go. Also you said post the values while it is charging, but the charger lights stays green, should I have that going on while I am measuring with the multimeter? Thanks!
 
Ok never mind that last comment you made it pretty clear where the multimeter pins go, will try that tomorrow and see what I can manage. Thanks!
 
yes, measure while charging. you will find one of the cells is close to or at the HVC and you will have to discharge the high voltage from that one cell to keep it charging up on the charger. so you have to get the pack open or just give up now.
 
Ok other dumb question. If I were to give up now would it be possible for me to put another battery pack on it for $2-400? Any tips on connecting to the bikes input port? I figure I could fashion a means of allowing the battery to be removable but secure, and could use the battery stock charger at my office. The main challenge from my perspective is connecting to the bike. Any tips on a good setup? It might be easier to spend a few hundred vs mess with the pack and the potential hazards.
 
I'll make a separate thread for that question, I'll try to read battery voltage first, should posts back in a few days. Thanks!
 
there are no hazards. it is just a hassle to get it open because of how they glue it together. follow the threads on how to open it but once you have access to the BMS then you will know which cells are the high ones and how far outa balance the pack is now.
 
You can check the pack voltage currently on the connector pins.
That will give you an idea where the pack is .
There is another thread over in the battery section about connecting up a different pack to the "B" port.
https://endless-sphere.com/forums/viewtopic.php?f=2&t=71243&p=1075399&hilit=A2b#p1075399
You will probably have to cut off the existing connectors as it hard to find those 5 pin female sockets
( I guess you could cut use the one from your current pack ?)
But really, it's a waste to junk the current pack just to save a little effort doing some fault finding...it's not that hard.
 
Measuring the pack voltage on the terminals doesn't always give the right answer. If the BMS is switched off, you can get anything fom 0v to actual pack voltage. You might get a better result if you measure the voltage on the charge socket as long as the charging FET isn't switched off or charge fuse blown.
 
Hillhater said:
There is only one socket on the A2B pack, and unless something has changed, only common pos and neg connections for charge and power discharge.
The one I worked on had a charge socket on the back. While I think about it, I remember an on/off button on it too, so to eliminate the obvious, does this battery have the on/off switch and has it been pressed? Maybe some all-round photos would help so that we know what we're dealing with.
 
Hi All, I am going to try the crack open method starting next week I have a wedding to leave for so I will be away for a few days. I agree I think knowing the cell voltages is the way to go. I have press on off nothing lights up happens. Will send pictures next week and an update. Thanks!
 
He needs o open it to get the cell voltages.

I got mine open by heating up the aluminium case until it was just about too hot to touch. I used a hot air gun. I then levered off the ends with a screwdriver, but it left a lot of lever marks. The problem is that the ends are glued on with silicone sealant. Obviously, you need to remove all the screws and pegs first.
 
It's definitely silicone. I tried for hours to get the ends off before I had the idea of heating. It's still not easy, but the heat definitely helps. The heat doesn't melt the silicone, instead it just releases a bit of the grip.
 
Hi all got it open not that bad at all. Hammer and screw driver on bottom of the "u" in the middle to start then work around. Got it open in about 20 min no heat needed just put on solid ground give it a good wack and work your way around. So now the question is how and where exactly should I measure the cells? When I peel on side in the middle I see a red and black wire but not sure if that helps since it is a whole group.. Next idea was the main board there but to take that off its like 4 bottoms of bolts not as obvious looking as screws so not sure if I should even mess with that and just find a way to measure the cells individually or as a group some other way. Anyways here are some pictures https://www.dropbox.com/sh/bu6415rjjbpi38g/AACpYvPcpH5MIY1Hu8Dqgi0oa?dl=0

If someone can offer guidance on where to measure and how ill try later tonight or tomorrow and will post values here. Thanks!
 
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