Help, again, re Charger for the LIPO4's

[mvadventure]

I'm still trying to download pics and post but in the meantime I'm suffering a technical glitch.

The new LIPO4's have 26.3 miles on them. They started at 53.6 volts and are now at 50.6 volts and the charger isn't working!

Since it's the weekend I can't get hold of Zane. Here is what I know:

The charger is a Li-ion charger, Model JSC 1175A 13s/2A. The green charge indicator only comes on when it is plugged into the wall and not plugged into the battery. The fan does not run. There is no power when I plug a meter into where it is supposed to go into the battery. The inside of it shows no apparent damage and the little fuse tests good.

For what it's worth the SN is 027269 and the D/C is 200706.

After a 16.5 mile run yesterday th battery went from 53.2 to 52.6 which was great. A high speed run of 6.3 miles is the balance of mileage. The range appears as though it will be great if I can ever recharge them.

Any ideas on the charger? Can I use my SLA charger?

Mike

 

[Jozzer]

For emergencies you can use your SLA charger, providing you monitor the cell voltages and stop the charger at the appropriate point. Better still if you have a DB or watts up so you can see whats going in current wise too.
Are these really LiFePo4? if so, cut off at 3.7v per cell, and you should be 90% charged.
Of course your SLA charger would need to put out around the right voltage (no more than a few volts above packs max charged voltage).

Having said that, I know nothing about your packs specifics, if some1 knows more wait for thier advice

 

[fechter]

I wonder if your charger is like Deepkimchi's.

You might take a peek inside and see if there is anything obvious.

 

[Beagle123]

The good news is that you won't do any damage to your batteries while you get a new charger. They like being stored at a lower voltage. Aparently, the best way to store lithium is at 40% charge.

I hope that we can find some really good charging solutions soon. I'm going to use a lab power supply to charge my batteries.

 

[Ypedal]

Beagle, i don't quite agree with the 40 % thing on these cheap Chinese LiFe cells.. the self discharge can be quite a factor, because of this i try to keep my pack fully charged, this gives more time before a potential weak cell dips down belo 2v !

MV : Do you have access to each cell ? can you test the voltage of each one independantly ? Does the pack have a BMS ?

What conectors were used on the charger ? a 2 lead or a multipin gimik ?

 

[mvadventure]

Finally got my pics downloaded so here are a couple of the batteries. Access to the individual cells is easy enough, all I have to do is cut a couple of dollars worth of wire ties away. I've added some heavy duty ones since the pic but I bought enough to allow for something like this.

Not the garden hose shock absorbers. Feedback here would be helpful, I was simply afraid not to provide some sort of relief.

I really need the bike tomorrow and don't want to change everything back to the SLA's so I'll do my best to follow Jozzers advice and use the SLA charger sparingly. I just have to make sure I don't get the + or the - crossed. Since the SLA charger has a three pin connector and the LIPO's have what looks like a computer 110 plug I''ll make mods to the batteries rather than take the charger apart.

I took the top of what I think is the BMS, the square aluminum sandwich on top of the batteries. Who knows, could have been a loose wire or something else obvious. I was surprised to find what appears to be caulk, still very wet, very messy, over some connectors along with some very lightweight aluminum strips apparently used to join them electrically. The strips were loose and moved around in the caulk once I took the top off and the caulk had squished well below the connectors onto the board. There was so much caulk the little aluminum strips with tiny Chinese writing were probably ineffective if they were designed to join the connectors/tabs or whatever they were. I didn't take any pics and should have.

If indeed I hook the SLA up and if indeed the batteries charge then the BMS questions is moot anway.

Mike

 

[Ypedal]

That white goop is most likely thermal paste ( it stays soft )

Those cells look curiously like Thunder Sky type ?? ( white box with ridges !!! )

But man.. that looks rough ( and i know "rough" !!!!!.. )

I'd like a quick snap of the charger if possible !

 

[Jozzer]

For temporary charge connectors i'd suggest bypassing the BMS and attaching a couple of leads directly to the pack, so + - is clear and you avoid giving the BMS any surprises
As long as you watch the pack whilst charging and keep an eye on cell voltages you should be fine. Watch out for warm cells too perhaps..


Steve

 

[mvadventure]

What I did, naturally prior to the message from Jozzer, was to cut the charger lead off of my SLA pack. Since the wires were clearly identified as red and black and the wires going into the battery, albeit through the BMS, were red and green, I felt 99% confident they would be OK.

So, I skinned a half inch of insulation from the negative charger wire on the battery and merely wrapped a couple of turns of wire from the SLA terminal around that and added the red wire to my positive lead. Since I have yet to obtain any Anderson Connectors it was simply enough to add the wire to the existing wires and put the wire nut back on.

Then, after hooking everything up and plugging the charger in, I tapped the switch for the charger and nothing snapped, crackled or popped. So I turned the key on in order to activate the watts up and did it again and the battery started charging.

When I received the battery there was 53.6 volts, after a brief test there was 53.2 and the decline from there is realistic. I monitored the charging cycle closely and shut it off when it reached 53.6 with the charger running. As soon as the charger cut off it dropped to 53.2 which was fine by me.

Naturally since it's a beautiful day and all I have to do is chores I really don't feel like doing, (and my bride isn't home) I went for a brief ride. The first two or three tenths of a volt went fairly quickly but then it stabilized and was using power at a reasonable rate despite the fact it was operating at 25 - 27 MPH. Upon my return I plugged it back in for a half hour and at 53.6 pulled the plug again.

I feel confident, at this particular moment, this will work until I get the charger fixed/replaced/tossed in the ocean.

Whilst I was waiting on the charger and watching "Q" school on the golf channel I completed a project that Xyster would be proud of. I'll take a pic and post in another thread.

Thank you very much for giving me the confidence to use the SLA charger. It really sucked to have these brand new, ugly or not, batteries that were giving me the range I need and having to change them out with the SLA's.

Mike

 

[Ypedal]

Ok.. one very important detail.. do me a favor.. and check each cell voltage and report back !!!

You want them all to show aprox 3.6v on full charge.. and no less than 2 to 2.3v during discharge.

The resting voltage on LiFe is not the same as LiPo( cobalt and manganese ).... so the 53v rest voltage could be misleading..

 

[Jozzer]

16 cells right? Since your only charging to 3.35v per cell I doubt there will be a problem with pack imbalance causing overcharging. If you can monitor cell voltages individually whilst charging beyond this point then you could charge the pack to 57.6 (3.6v per cell) safetly.
Probably you are only charging to 3/4 capacity.

Another way would be to watch overall voltage carefully in the final stages and stop charge once the voltage starts rising quicky (3.5v per cell on A123 batts, may be slightly different on those). You'll soon notice the difference when they are ready! Even if 1 cell is ready first, its voltage rise will be noticeable over pack voltage.

All this may be academic, possibly your SLA charger cant do much more than 53v anyway??

Glad your still on the road

 

[GGoodrum]

Actually, your 48V SLA charger can be used just exactly like you would with your SLAs. There is no need to manually stop it at 53.2V. Each of the LiFePO4 cells puts out a "nominal" voltage of 3.3V, so for your 16s setup, that is 52.8V. The optimum voltage these like to be charged to is 3.65V per cell, which for the 16-cell pack is 58.4V. The fully charged "resting" voltage is typically somewhere between 3.4-3.5V, or about 54-55V.

12V SLA batteries have 6 cells. Although the "nominal" voltage is 12V, or 2.0V per cell, the fully charged "resting" voltage is about 2.2V per cell, or 13.2V. For a 4 SLA series setup, the resting voltage is about 53V. SLA chargers typcailly use a cutoff voltage that equates to about 2.40-2.45V per cell, so a typical 48V SLA charger uses a cutoff of 57-58V. That is very close to the optimum 58.4V your 16-cell LiFePO4 needs.

All of the better SLA chargers use a combination constant current (CV) and then constant voltage (CV) charging profile. The charger starts out in a constant current mode, where the current is held to the maximum the charger can put out, and then voltage is allowed to climb up. When the voltage reaches the cuttof voltage (i.e. -- 2.45V per SLA cell...), the charger automatically switches to the CV mode where the voltage is held at the cutoff, and the current slowy drops down. When the current drops to somewhere around 10% of the maximum, the charging stops.

Almost all Lithium-based chargers work exactly the same, and use a CC/CV charging profile but they just have different cutoff voltages. For Lithium-Cobalt chemistries, the cutoff is 4.2V per cell, and you'll have quite the fireworks show if the charge voltage exceeds this value. With the much safer LiFePO4-type cells, the optimum cutoff is 3.65V per cell, but they can go over this without problems, but you might eventually shorten the cell life if you make a habit of doing this.

If you stop the charger right at the cutoff voltage, the cells will only be about 85-90% full. The CV mode is what provides that extra "topping off" so that the cells can be fully charged.

In any case, you can pretty much have a drop-in replacement for any SLA setup by using multiples of 4 LiFePO4 cells is series (i.e. -- 4s=12V, 8s=24V, 12s=36V, 16s=48V, etc...). The nominal voltage is higher (12V vs. 13.2V), mainly because SLAs have larger voltage sags under load, but the fully charged "resting" voltage is very close (13.2V vs. 13.8V), as is the optimum charger cutoff voltage (14.7V vs 14.6V).

Before charging you can check to make sure the cell voltages are all fairly close (under .2V difference between the lowest and the highest is okay...), and then let the SLA charger do its thing, all the way to the end. You should then end up with a pack resting voltage around 56-57V.

-- Gary

 

[mvadventure]

Wow, It's hard to explain what all this help means except it's great and I thank each of you.

The resting voltage of each cell is 3.29 when I cut it off at 53.2. Now that I understand it's ok I'll let the charger run a little longer. Each cell measured 3.29 exactly with no variance.

I took a pic of the charger for ypedal.

Zane did email me and I believe he understands the problem. I'm waiting to hear back from him to see if I need to hit the charger with a hammer or if he thinks it's something else. He is in Singapore which slows down communication somewhat as he wouldn't be there if he wasn't busy.

Mike

 

[recumbent]

Wow, this is one very informative thread. 8)

Good luck, "mvadventure" with the broken charger when you get it back. Sure is nice to know we have a back-up charging system readily available.

Thanks to all that participated to this bundle of information.