BMS and Charger questions

[redorblack]

I see a lot of people are using the Signalab V2.5 BMS. apparently sourcing them from Ping. I don't see him listing them on his website separately... are some of you buying just them to replace the Headway BMS setup or scavenging them from Ping battery packs?

The thing I did see on Ping website... an option to upgrade to a 9A charger with the 48V 30ah pack. Anyone get just one of those? Would it work ok with a Headway 16S pack? I'd be under 1C with my 48V10Ah Headway pack... the idea of tripling the charge rate from the 3A charger I got along with my Headway pack (at least for a good portion of the charge) has a lot of appeal.

Is there a downside to running a 9A charger... maybe not balancing the cells as well? I'm thinking a cell would hit HVC and the pack wouldn't get a chance to balance out through the stock BMS? Would the Ping not fill the Headway cells due to a bit lower charge voltage?

I have been a bit concerned about my Headway pack having 2 cells a bit lower than the rest, while 14 cells are 3.6-3.7v when the charge cycle with the matched 3A charger, one was 3.58v and one stays under 3.4v. I found a wall wart 500ma 4.5v power supply and cut the charge plug off it and wired it to the low cells and plugged it in while monitoring voltages. I brought the 2 cells up to about 4v and let them rest, (only took a couple of minutes) then hit them with some juice again when they dropped back down under 3.65v. I just checked current and the "500ma" power supply was putting 860ma out when I applied it and went down to about 600ma after a couple of minutes. I disconnected it and switched back to voltage and the cell is up to 4.02v. Am I hurting the cell or just getting it closer to topping off? It dropped back to 3.65 in the amount of time it took me to walk back here to the computer and write those last two sentences about checking current and voltage...

 

[dak664]

I think those voltages will reduce the capacity and lifetime. 3.65 is full charge, anything above that starts degrading the intercalate. It would be an interesting experiment to see what a good whack does to a cell at 4 volts vs 3.3 volts

3.55 is practically full, within 0.1AH I'd say. Under 3.4 could be anything, 5AH or more. But if they charged up beyond 3.65 they are as full as they can get (anymore).

 

[dogman dan]

I've read others say that 4v will ruin specific models of lifepo4 cells. Not killed, but lifecycle reduced by it. I wouldn't do it again. Pings charger and bms stops at 3.75, and is considered a high charge.

Is this a new pack? New lifepo4 does need a few cycles to start balancing nice, and so does lipo. A few cells at 3.4 will reduce the capacity of the pack, but I think it's pretty well proven that a slight undercharge is beneficial to cycle life. So is both charging and discharging at more moderate rates.

Do you need 9 amp charging? Or you would just like it. 5 amp charging would fill you in 2 hours, I'm using that rate with my pings, and it seems quite fast enough for my needs. But I have lots of battery, and can carry 70 mile range easily.

Now that I'm going over to lipo on my "fun" bikes, I realize that if I needed just a few more miles I could carry 5 ah of 10s (40V) in a really tiny package as an emergency reserve.

You can buy singalab bms from ping by just asking in an email. Also High Tech Bikes can sell you one, again you may have to ask for it in an email.

 

[redorblack]

I've read others say that 4v will ruin specific models of lifepo4 cells. Not killed, but lifecycle reduced by it. I wouldn't do it again. Pings charger and bms stops at 3.75, and is considered a high charge.

Is this a new pack? New lifepo4 does need a few cycles to start balancing nice, and so does lipo. A few cells at 3.4 will reduce the capacity of the pack, but I think it's pretty well proven that a slight undercharge is beneficial to cycle life. So is both charging and discharging at more moderate rates.

Do you need 9 amp charging? Or you would just like it. 5 amp charging would fill you in 2 hours, I'm using that rate with my pings, and it seems quite fast enough for my needs. But I have lots of battery, and can carry 70 mile range easily.

My Headway pack I got last Veteran's Day, and has somewhere between 500-1000 miles on it (running it on both a Rans Wave and a Greenspeed GTO trike), mostly fast in city commuting. I opened it up because I'm concerned about the range, around 15 miles rolling at a 25 mph average speed riding in city traffic (about 28-30mph cruising speed). That's when I found the one cell around 3.34v with the rest between 3.58 and 3.70v (most either 3.65 or 3.70) right off the charger. I've got a cycle analyst on the Wave, but don't trust the calibration. I think now that I have my good power graphing multimeter back home, I'm going to run it til it hits LVC and open it back up to measure the cell voltages and see if it's the one cell weaker that is kicking it off or if the whole pack is down. I wish I had a stable 10 amp load I could throw at it through the controller and set the calibration correctly.

As for the 9 amp charging... if it wasn't much larger or heavier than the 3 amp charger I have, I'd carry it with me for opportunity charging, the difference in how much juice I could get back while having an coffee or lunch stop is pretty significant. I could about do a full recharge while grabbing a meal. It doesn't make any improvement if I'm just doing an overnight or during the workday recharge where there is 8+ hours available, but if I'm looking to extend my range on the road, it's pretty significant.

 

[dak664]

At that current there will be very little equalizing at the end of the charge, the BMS will disconnect within a few seconds once any cell is full. It needs to stay on for a few minutes at 150 milliamps each time, or a few hours at 150 milliamps every 50 cycles or so. An easy way to limit the current is put a 10 ohm resistor in series.

 

[scoot]

That's when I found the one cell around 3.34v with the rest between 3.58 and 3.70v (most either 3.65 or 3.70) right off the charger. I've got a cycle analyst on the Wave, but don't trust the calibration. I think now that I have my good power graphing multimeter back home, I'm going to run it til it hits LVC and open it back up to measure the cell voltages and see if it's the one cell weaker that is kicking it off or if the whole pack is down. I wish I had a stable 10 amp load I could throw at it through the controller and set the calibration correctly.

I believe that you may have a quick remedy at your disposal (maybe not, but worth a try perhaps). If it were me, I would perform a single cell top off on that 3.4 cell with a single cell charger following one of your normal charge cycles. That would ensure a complete balancing and may totally resolve your problem. If that cell, or any of the others is a truly weak cell, then my guess is that you will need to observe a discharge graph under load. If your suspect "weak" cell is one of the first 8 in the series then you could plug in a CellLog8s into the JST-XH connector that plugs into your BMS and go for a ride ? Then upload the data in the Logview software and look for that cell to be discharging at a significantly lower voltage than the others. But then again, if the single cell "top off" works then you may not need to bother with that. I have concluded that a single cell charger is one of the most useful tools in my collection.

Once the pack is completely balanced, then the BMS (any BMS) may have a better chance of keeping it there. And based on the Headway BMS reputation, I would upgrade to a more known reliable one too... JMHO.

edit: and yeah, I agree with what what dak said about the high charging current limiting what the BMS can accomplish... I've sean that in action myself.

 

[redorblack]

Ok, I took my Wave out for a ride and went to meet up and cruise with some friends that are riding STP today. I ran it til the pack shut off, then pedaled to a local coffee shop. Took the pack out of it's case and measured individual cells.

I got this...

2.90... 2.85... 2.85... 2.78
2.88... 3.00... 2.73... 2.51
2.97... 2.97... 2.88... 2.85
2.80... 2.90... 2.88... 2.97

That 2.51 (unloaded and having 'recovered' for 15 minutes or so) is the same cell that's been lower charged as well. According to my Cycleanalyst I went 25.8miles averaging 20.1mph and used 6.68Ah. The pack should be 10Ah, but it could be that I am screwed up on my calibration on the Cycleanalyst.

My thought is that rather than trying to top off the low cell once the regular charger thinks it's full, maybe I should single cell charge it from discharged for a while, at least until it catches up with the rest of the pack, then let the main charger finish it off. Would hitting it with the 4.5v wall wart be a problem with the cell low?

Interestingly... the 3.00 is the cell that was reading 3.58v before while the rest were 3.6-3.7v and I hit that cell with the wall wart a few times to get it's voltage up with the rest last night.

Also I've just been attaching the bare wires from the wall wart to the screws on the cell and then plugging it in... I'm not trying to go through the BMS or disconnecting the cell from the rest of the pack.

 

[dak664]

See my discharge curve at http://endless-sphere.com/forums/viewtopic.php?f=14&t=13717
2 volts is the headway BMS cutoff. I'd say your pack was fairly balanced, the 2.8V cells wouldn't have more than 0.5 amp-hour in them. But, assuming the BMS is working properly your pack would be guaranteed at absolute maximum charge if you gave it 50-100 ma for 10 hours or so.

[Edited] Meant to say, 10 hours of low current equalizing after the full charge cuts off.

 

[redorblack]

I just plugged the wall wart in on the cell that was lowest... went to 3.14 with the power supply plugged in. I did a bit of pack charging and the stable cells are around 3.22v. So I'm going to let that cell charge until it hits that for a while and then put the pack back on it's charger. Maybe I'll go get a resistor as recommended and make some jumpers so I can put that in line with the main charger in order to get the pack balanced further.

BTW, the cell is up to 3.22v and seems to be staying there... under the assumption that it might be about a .5Ah under the rest, I think I might just let it suck up power for about a 1/2 hour to an hour unless the voltage rises further. This might get it in line with the rest of the cells.

Edit: Just pulled the power off the cell after about a 1/2 hour, my meter was flicking from 3.22 to 3.24v at about a 50% duty cycle. With the power supply off it's steady at 3.22v. I'm going to let the cell rest for about a half hour and see if it stays there. If so, I'll put the pack back on it's charger, if not I'll juice that cell a bit more. Maybe all I'll get out of this is a .25Ah to a .5Ah more range, but my goal is to feel satisfied I don't have a bad cell. If I do, I'll replace it. At least if I get it close, doing a trickle charge at recommended won't take forever.

 

[scoot]

You might inadvertently make it more out of balance with that approach I'm afraid. That "bottom balancing" approach may just make more work for the BMS in the end... it works on a top balancing approach.

Again, suggest doing your normal charge (lower current if possible) , then see where you are at again. At that point when all of the cells are above that 3.5 level, then you know at least they are equally charged, except any or the one that is still in the 3.3 range.

If the suspect cell is still low, attach you 4.5 volt charger to the suspect cell (don't need to disassemble any thing) and watch that cell carefully/constantly with your volt meter... disconnect it when it reads 3.8 volts and all should be balanced (filled up).

And I tend to agree with dak again... that 2.5 one does not seem too far off (maybe a 1/2 ah or less) than the rest of them.

 

[redorblack]

Thanks Scoot,

After letting the pack rest about 40 minutes, the 'weak' cell is now right in the middle of the voltage of the rest of the cells. Hooked the pack charger back up and it's also right at the average of the charge voltage the rest of the cells are at. I'll check it as it continues to charge as a pack, but I think that might have been all I needed since the BMS shuts off rather than putting any juice in with the stock 3A charger once the majority of cells have hit the HVC. Or, I suspect the charger is shutting off when it sees a certain current/voltage combo, only popping back on once the surface charge drops a bit, and with it hitting the pack with 3A, it just flicks on for a fraction of a second a couple of times and then gives up again.

When I first got the pack, I was monitoring charge voltages with my graphing meter and saw a lot of this on and off activity with the charger supplying 63 volts while flipping on and off. After a few cycles of using the battery I didn't see that anymore and I considered myself a happy camper until I tried doing a round trip to work and back thinking I'd only used about 1/3 my capacity getting there. I didn't make it a 1/3 of the way home... but I chalked up the 6.6Ah used or so (on a 10Ah pack) to the cold (was significantly below 0c).

I need to find something to load the pack with a 10 amp draw in order to calibrate my CycleAnalyst properly and to see how long the pack will actually last at 1c.

 

[pgt400]

I've been using the SignaLab V2.5 for the last couple of months. Works great. Using it with a 16S3P A123 pack. All the cells peak at 3.6v within 30 seconds. I did balance the cells with a single cell charger first as the SL BMS bleed current is low. I've never hit the LVC yet, I usally just charge after 10 miles, picture below shows all 16 LEDS on at full charge.View attachment DSCN1859[1].JPG

 

[gblast123]

Is there any way to obtain the ping 2.5 version without the battery pack?

I emailed Ping and they told me that it was not for sale without the battery.