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Old 09-25-2021, 08:36 AM   #21
Volt_Ampere
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Default Re: Starting my EZGO Marathon Lithium build.

I would put the balance leads right on the battery. That current is small enough that it won't affect the shunt's measurements of current drain.
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Old 09-25-2021, 12:23 PM   #22
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

I would normally agree with that. A balance lead right on the cell is best. But I really believe that the black lead coming out of the balance plug simply powers the BMS and Bluetooth module, seeing that the first two cells were zero volts without the B- from the high current side connected. I can't explain why it was the first two cells though. I could see the first cell showing zero if the reference was the B- of the high current side, but why the second cell? Seeing that the other 12 cells showed the proper voltage, obviously they read the two leads tied to each cell. That second cell has a regular balance lead on each side of it, just like the upper 12 cells. Why would it read zero?

It does not make any sense. You would think that voltage measurement for all the cells would come from the balance leads. And that it would use the black lead on the balance plug as the common reference.

And the secondary concern is that I don't feel that it would be good for there to be a difference of potential between the black wire of the balance plug and the B- of the high current side.

But I guess that a maximum of 75mV difference of potential, and only at 500A of current draw isn't bad.

Maybe as an experiment, hook the black wire of the balance plug straight to the cell. Watch the cell voltage reading on the app at high amp draw. Compare that to a voltmeter reading of the first cell at the same time, and see if I can see the 75mV difference.

Like I said, probably overthinking this.
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Old 09-25-2021, 12:42 PM   #23
Volt_Ampere
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Default Re: Starting my EZGO Marathon Lithium build.

It probably makes no difference but if it's part of the BMS cell voltage measurement, you don't want any extra voltage drop in that cell measurement. Cell measurement with any decent BMS is differential between each cell - not all referenced to negative.
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Old 09-25-2021, 08:19 PM   #24
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

Yeah, it was just weird that the first two cells showed no voltage without the B- on the charging side hooked up. I hooked the black wire straight to the cell.

Today I got the shunt installed. I added some more fuses, obviously because any wire attached to B+ should have a fuse a close as possible to B+. That way if there is a short in the wire, it will blow the fuse back at the battery, and not burn a piece of wire.

I added a fuse for the voltage converter. There is a fuse inline with it, but it's right at the converter. A lot of good that will do if the wire gets nicked between the converter fuse and the battery.

I didn't run the multi-conductor cable from the shunt to the front of the cart, but I did plug in the display and tested it. It does show that 10mA is flowing all the time, that's something to watch. I took the cart around the driveway for a little bit, and I know I still have some tweaking to do in the Alltrax. But the maximum battery amps I saw during acceleration was 60A. Cruising constant speed on level ground was between 5A and 12A. In my few minutes of running around the drive, I didn't use any AH, it still said 0.0AH. Something to note is that the polarity is based on the battery's point of view. Loading it up during running shows negative amps.

I decided to try a little bit of charging while I was supervising it. I checked the voltage again on the charger, and plugged it in. Earlier in the day I had cut the smaller DC side connector off the charger, and crimped on terminals for the Anderson SB50. At first, no current was flowing. I started to get worried, then I realized that I had not attached the wires from the charging port to the B+ of the battery and C- on the BMS. So I shut off the charger, attached those wires, and all was good. It was pulling about 9.7A, and the charger is rated for 10A. I watched the app and the cell voltages started to rise. After 30-40 minutes, almost 9AH went into the battery. I let it run until all the cells got to 4V. The max cell differential I saw was 0.018V. As far as I can tell it didn't get into any balancing, but the charging current was starting to taper off.

Tomorrow I'll allow this set to charge and balance, with supervision. Then I'll hook the balance leads to the other set of batteries and charge and balance those. After that I can install my jumpers to parallel up the two sets of batteries.

Maybe I'll start to run the wires under the cart for the 12V to the front for the headlights and the radio. Along with that I'll run the multi-conductor cable for the monitor, and start looking into installing the display and the radio.
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Old 09-26-2021, 08:43 PM   #25
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Default Re: Starting my EZGO Marathon Lithium build.

As I laid in bed this morning, I came up with an idea. I've been thinking about these balancing leads wrong all along. When I look under the seat now, I see this huge mess of wires. Most of that mess comes from having those balance leads tied to each of the plates I added to each cell.

The batteries have a plug on top of them for the balance leads from the BMW system. Battery Hookup threw one of those plugs in the boxes for each of the 4S and 5S units I bought. The garage has been a bit of a mess, but I found 4 of those plugs out of the 6. I'm sure the other two are somewhere, but I really don't need them. Once the units are all paralleled up, I only need 3 balance plugs.

Of the 4 plugs I found, 3 of them had 8 wires, and one had 9. I would figure that the 5S units would have the 9 wires. Since I have 2 4S units and 4 5S units, I would think that I would have 4 plugs with 9 wires, and 2 plugs with 8 wires. Unless Battery Hookup made a mistake and threw in the wrong plugs, which could have happened.

I stripped the wires of both an 8 wire and a 9 wire plug, plugged each of them into both a 4S and a 5S unit, and measured voltages. After a little figuring, I determined the pinout. I decided to make all the plugs I'll use the same, even though I only need the B- for the unit at the low end of the series string. But it makes sense to make 3 plugs the same, and just not use a wire if I don't need it. I looks like the 8 wire plugs don't bring out a wire that's tied to the B- of that unit. I'm assuming that they get the connection from the B+ of the unit in series under it, since that wire was brought out on all the plugs, whether it was a 8 pin or 9 pin. I was able to use a razor blade and move a pin in the plug from pin 1 to pin 12.

I then decided to pull the cart outside and put it back on charge. I let it charge about 3 hours, and it's still not fully charged. I think it's close though. Charging current was under 1A. The BMS app said there was 14 minutes left. Not sure how to interpret that though.

Tomorrow I'll finish building the three plugs, test them, then cut off the 1/4" ring terminals and solder the wires to these three plugs. I'll test it at the plug for the BMS again, and then finish charging the first string.

I also figured I'd throw in a current pic, since I haven't added one for a while.
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Old 09-26-2021, 10:47 PM   #26
Volt_Ampere
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Default Re: Starting my EZGO Marathon Lithium build.

I agree that's a rat's nest! Be very careful when working with the balance leads. You can fry them instantly if you short them together. If it's on a plug, don't plug it in until you have all of the connections sorted and double checked. I was real careful working with the balance leads on the Leaf cells I recently got because I did not even have access to the internal connections of each 7S module.
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Old Yesterday, 11:39 AM   #27
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

I agree on the rat's nest. Other than the balance leads, all the rest of the wires are run in a "path" and will easily go into some split loom tubing. Putting the balance leads into the plugs will knock that part of the rat's nest down to three distinct runs of split loom tubing.

Yes, I'll double and triple check as I solder the plugs on. Then ohm things out. Then plug in one battery unit at a time while checking voltages on the unplugged BMS plug. The I'll unplug the three battery plugs, plug in the BMS plug, and then plug in the battery units starting with the B- end of the string.

Or I'm wondering if I should always plug in the plug at the BMS last. I was figuring that I could unplug these 3 plugs at the battery units to completely disconnect all current draws from the batteries for the winter. It's a little difficult plugging and up-plugging at the BMS all the time. It will be much harder after I put the cover on the box.

I'm wondering on your opinion if it would be safe to always plug in the battery unit starting at the B- end of the string, and then plug in the middle unit, then the top unit. Then on un-plugging, unplug the B+ unit first, then the middle, and lastly the bottom. What do you think?

I learned years ago while installing a remote start, always connect the main ground wire first, before hooking up anything else that can supply power. That way if any current is going to flow, it will go though the intended and designated path, not some unintended case or antenna connection. Those unintended paths could have very small circuit traces and not handle the current.
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Old Yesterday, 01:59 PM   #28
Volt_Ampere
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Default Re: Starting my EZGO Marathon Lithium build.

I would plug in the BMS connector last. Not sure it matters but that would be my choice.
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Old Yesterday, 08:25 PM   #29
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

Yeah, that's just going to be a pain. The plug is hard to work with anyway, and it's in the box so I would have to take the 6 screw out and take the lid off.

I did get the plugs installed today. It was pretty easy. By the time I got it done, the wife was home from work, and she wanted to eat dinner, so it really wasn't worth pulling the cart outside and putting it on charge, to just be done for the night anyway.

Hopefully I'll finish the charge of the first set tomorrow, and then start charging the second set.
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