Serious strangeness from 36v EVC Headway pack.

[StudEbiker]

Okay, I have one of the closeout 36v Headway packs with the matching rear carrying rack. Here is the strangeness. When I run a wire from the charging port and test the voltage I get a reading around 38v, however, if I run that same lead to my Turnigy watt meter, the meter stays dark. I have two other packs here that I have tested the same way and the watt meter is good, so you can forget about the meter being bad. I also have the light bulb set up. Remember, I am definitely getting a volt reading with a multimeter across the wires. When I plug the light bulbs in...butkus. Nothing. So now I have a charger on the pack, the red light is not coming on and I have the watt meter in between the charger and the battery. The meter is not showing that any juice is flowing into the battery, just showing a voltage of around 44.6v. Can you think of any reason the wires would have voltage but not show on a working meter or light the light bulbs? The only think I can think of is if the meter and the bulbs are both drawing so much current it is tripping the lvc, but I don't think that's the reason.

[StudEbiker]

Okay, so I lfet it on the charger for awhile and went back and tried it again and this time it came up, but the reading through the watt meter was only @ 36.31v. Does anyone know what the LVC on these headway BMS is? If it is 36v, then it may have been tripping the BMS. If that is the case then I may have a problem with this pack because the red light is not coming on the charger when plugged together. I was a little concerned about this pack already, but I thought it might just need to be cycled a few time to get it balanced, but it is starting to look like it may be worse than that.

[Ypedal]

It's time to open it up and take a look inside ( something that should be done on any headway pack regardless.. check for loose wires etc.. )... check the cell voltages directly.

[StudEbiker]

Yeah, I have the pack open and all the wiring looks okay. As far as checking the individual cell voltages, I am not sure how to do that. Should I check them at the multiwire connector that connects to the BMS?

[dnmun]

don't short out the sense wires.

[Ypedal]

^^ what he said ! lol..

but start by checking each cell at the + and - terminals and report back first.

[StudEbiker]

okay, will do.

[StudEbiker]

I had a chance to check the cells and.....I think I found the problem. Eleven of the cells were between 3.327v and 3.493v except one. It was at .468v. Okay so now what?

[snowranger]

Try single charging that low cell to see if you can wake it up. Otherwise, it's toast and you need to replace that cell. Didn't EVC at least warranty the cells if not the bms?

[StudEbiker]

Can I single cell charge with one of my 36v chargers here monitoring the voltage as I charge or do I need one of the special single cell chargers that I have seen advertised on here? No, EVC doesn't even exist any longer I don't think, so no warranty on the cells.

[dnmun]

if you can get a single cell charger and charge up the low cell, you may be able to see if it will hold a charge. i see that the voltfreaks are on sale now too. tony tieger just ran an ad today.

[snowranger]

You might be able to use a cell phone charger. They'll typically end at 4+ volts, but you can remove it when the cell gets to 3.7 volts. Are the cells the screw tab kinds or soldered?

I recently bought one of those 48V headway packs from EVC before learning about their debacle. I was kind of disappointed to find out the cells were soldered. If anything were to go wrong, I'd be hosed without a solder tab welder. My pack was ridiculously out of balance when I got it (only got 8.6 ah out of 20 on the first discharge), but seems to be okay now after manually balancing. There were no cells as low as yours though.

[dnmun]

you can cut the tab on those welded cells, the replacement cell has another tab spot welded on each end and you just solder the tabs together.

if you get the single cell charger, you can cut off the plug and solder some alligator clips on the end of the cable and then you can charge any cell in the pack by clipping on to each end of the cell, just use common sense and don't reverse polarity on the connection or clip it on another cell.

[snowranger]

Thanks Dnmun. Hope I never have to do that. It does look like these headway packs are overbuilt which is good.

[StudEbiker]

I lucked out and found a 3.7v cell phone charger at Goodwill today. It even has two separate wires so it should be pretty easy to splice on some clips. Wish me luck!

[StudEbiker]

Well, the Nokia charger that is clearly marked "output: 3.7v" is actually outputting 8.64v according to multimeter....glad I checked. Can I still use this charger as long as I monitor the voltage as it's charging??

[dnmun]

tony has the single cell charger on sale.

[StudEbiker]

Yeah, but they are not going to be in stock before the end of the month. This is for a build I am doing for someone else. If I can't wake this cell up then I need to move on replacing it. I saw on another thread that L4P said that once a cell goes below 2.8v it should just be tossed so I'm thinking this may be a fruitless pursuit anyway.

[Ypedal]

the nokia charger will drop down in voltage the moment you put a load on it with a cell.. keep a close eye on it but should be fine.

that cell is more than likely toast, i've been able to revive a PSI cell below 2v but it makes the BMS work overtime trying to make it match the other healthy cells... nothing to loose by trying to save it.. but don't expect it to work.

[snowranger]

Yes, the cell phone charger will drop down. They all use 3.7 volt lithium ion batteries.

[StudEbiker]

The saga continues. So I spent some time getting the charger all wired up with a watt meter inline so hopefully I could monitor the charge as I was charging (which didn't work so I guess it was below the working voltage of the meter) and then I connected the clips to the runt cell. Boy, it didn't take very long for the voltage of the cell to come up! Took the charger off and put the multimeter on it and I could see the voltage falling fast. Did that a few times to see if the rate of descent would slow, then I thought maybe I would charge the cell up to 3.6v and then plug the 36v charger into the pack and maybe that would help to hold the cell voltage up in the 3.6v range. When I did that I was somewhat shocked to see the voltage on the runt cell go to about 7.6v in the blink of an eye. After playing around with it a little more it seems that the BMS is sending twice the charge to that cell which of course is ridiculously too high for the cell and is probably what ruined it in the first place. So is there anything I can check beyond what I have done or am I looking at replacing the BMS and the bad cell? Man, I am more than a little frustrated with these packs right now.

[Ypedal]

The entire pack is seein the same amount of power from the charger, the BMS canot feed the cell extra power, however it is supposed to shut down the charger when that cell goes over ~3.8v or so... this indicates that the BMS is either faulty or there are other problems here..

That cell is a paperweight unfortunately... it went that high in voltage because the rest of the pack is charging and that cell is as full as it can get so the voltage shoots up high very fast..

[dnmun]

where did you measure the 7.6V and did it ever measure the 3.5V that you mentioned?

[snowranger]

Are you sure you aren't measuring two cells in series, i.e. 7.6/2=3.8?

[StudEbiker]

where did you measure the 7.6V and did it ever measure the 3.5V that you mentioned?

I measured the 7.6v at the ends of the cell. I was careful to place my leads in the same location every time I took a reading, so I don't think it is possible that I was reading two cells. I never got the cell to hold at 3.5v, when I put the Nokia charger on it, the voltage would go up very fast. So I got the cell in the 3.5 range and then (as the voltage was falling) I put the 36v charger on the whole pack.