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Unread 10-22-2019, 02:49 PM   #71
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Default Re: Lithium hunting cart overhaul

Has anyone using a BMS had the issue of the actual cell voltage (as measured using a digital multimeter) being off by 70-80mV? My cells actual voltage rating is 3.92 (a couple at 3.91), and the cells range anywhere from 3.91 up to 3.97.

Is this something to be concerned about?
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Unread 10-22-2019, 03:37 PM   #72
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Default Re: Lithium hunting cart overhaul

On your previous post you posted a picture of your setup screen. In that screen it shows an item called "Balance stop Diff Voltage" and you have that set at 5mv (.005V). Your cells are 6mv (or .006V) apart. So, I think your BMS is doing exactly what you told it to do.

Were it my BMS, I would want the balance V to be closer.
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Unread 10-22-2019, 04:37 PM   #73
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Default Re: Lithium hunting cart overhaul

I don't think he quite explained it right, from what I understood from our PMs and why I told him it is a concern is because:
1) If You use your meter directly at the battery posts, the voltage needs to be the same as measured by the meter at the end of the wires where they connected to the BMS, there is not enough length or current to cause a measurable drop.

2) If the BMS is measuring all cells off by the same percentage as the meter, then it is just a calibration issue, but if only a few cells are different, that is a wiring issue.

3) The BMS 16T specifies -5mV/+5mV accuracy on their ADC inputs so 70mv is way off to just be a tolerance factor.

I think he has a bad crimp or pinched wire or perhaps a bad connection in those wires.
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Unread 10-22-2019, 10:51 PM   #74
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Default Re: Lithium hunting cart overhaul

Sergio, if i had a bad connection or bad crimp, wouldn't I get a different voltage when I back probed it at the wiring harness? When I do that, I get the exact measured voltage on the digital multi-meter at the battery for each one. However, the BMS doesn't read that way.

I told the manufacturer this in an email, and I sent him a picture of my BMS readings, and he says it's a calibration issue.

At this point, I am thoroughly confused. I think I am going to send it back, and also get two new wiring harnesses (just in case).

DaveTM, the photo I posted about those settings that you re-posted is not my actual unit. I was asking what folks set theirs too. In any event, mine aren't .006 volts are apart, they are .07 volts (70mv) apart for one cell and about 30mv apart on the others.

Final question, probably for Sergio, if I removed all the connections and just connected the wires to the battery bolts and screws, wouldn't that eliminate any possible crimp or improper solder issue? That way, I could really see if it's a crimp issue?
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Unread 10-22-2019, 11:46 PM   #75
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Default Re: Lithium hunting cart overhaul

I thought Your meter read different at the BMS (back probing) as well, that was my #1 comment about the length of the wire not being an issue.

Since the voltage reading is the same at both ends of the connections the wiring is not an issue.

I would not feel comfortable with that margin of error, it could be a symptom of other internal issues on the BMS and that is one piece of equipment You need to be accurate when detecting high and low cell voltages.
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Unread 10-23-2019, 12:22 AM   #76
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Default Re: Lithium hunting cart overhaul

Quote:
Originally Posted by Sergio View Post
I thought Your meter read different at the BMS (back probing) as well, that was my #1 comment about the length of the wire not being an issue.

Since the voltage reading is the same at both ends of the connections the wiring is not an issue.

I would not feel comfortable with that margin of error, it could be a symptom of other internal issues on the BMS and that is one piece of equipment You need to be accurate when detecting high and low cell voltages.
Initially, I had three cells showing zero. The cell following those was, according to the BMS at 4.48. I knew that wasn't right because the digital multimeter was reading 3.92 at the battery.

You then told me to back probe. I found that the three had a crimping problem. I then fixed it.

At that point, it became apparent, that the BMS was still reading the cells as being higher than actual, some such 20-30mv, two as high as 60-70mv. Oddly enough, the first one and last one are accurate.

I haven't removed all the ring terminals or butt connectors, and just connected the wire to the screw/bolt, but I may. If I'm going to send it back, may as well try that first.
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Unread 10-23-2019, 08:44 AM   #77
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Default Re: Lithium hunting cart overhaul

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Originally Posted by MyCousinVinnie View Post
If I'm going to send it back, may as well try that first.
That sounds like a good plan!
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Unread 10-27-2019, 09:02 PM   #78
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Default Re: Lithium hunting cart overhaul

Update - I removed all the ring terminals and just tried the wire to the taps. That’s didn’t solve the problem. I sent it back the manufacturer per his request. Hope this works.
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Unread 10-27-2019, 09:03 PM   #79
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Default Re: Lithium hunting cart overhaul

Update - I removed all the ring terminals and just tried the wire to the taps. Thatís didnít solve the problem. I sent it back the manufacturer per his request. Hope this works.
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Unread 12-31-2019, 04:22 AM   #80
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Default Re: Lithium hunting cart overhaul

Quote:
Originally Posted by MyCousinVinnie View Post
Update - I removed all the ring terminals and just tried the wire to the taps. Thatís didnít solve the problem. I sent it back the manufacturer per his request. Hope this works.
Did you end up fixing the issue? Also, any chance of an updated wiring diagram with the relay, shunt, fuses, etc? I'm looking at going the Chargery route on my build.
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