QNBBM 8S

[Horsefly]

My QNBBM 8S active balancer arrived yesterday and I hooked it up. In my 8S pack of the little Navitas 25Ah cells, I have one that refuses to stay balanced with the others, so I was anxious to see how well the active balancer works. This pack is just for me to educate myself until I get around to buying larger cells, so although I would have hoped to have 8 good cells, I'm actually kind of glad I've got one misbehaving cell so that I can test the balancer. The Overkill BMS with passive balancing was not up to the task.

So far I'm pleased with the QNBBM. When I hooked it up the bad cell was about 170mV below the others. I did a brief discharge and then a charge (each about an hour), then left the pack alone with no charging or discharging. This morning the difference was only about 15mV.

Of course, there's no documentation for the balancer, and what I've found on-line seems to mostly be explanations of what it does for the purposes of selling more of them. If anyone has found some useful documentation, I'd love to get a link.

One thing that is a bit strange. There is a constant high-pitched tone coming from the board. It isn't really loud and so doesn't cause a problem, but I can't figure out what is causing it. At first I thought the sound might be only when it is performing energy transfers to make the pack balanced, but this morning they were well balanced, and it was still making the sound. Anyone else notice this? Any idea what the sound is from or what it means?

 

[snoobler]

I have the QNBBM single balancers you chain together. What you're hearing is "coil whine." I have single cell ones for Lithium and 12V ones for lead-acid. They all emit that whine. Some more than others.

They will attempt to balance at all times. If your usage exceeds 2A, they won't be able to keep up.

 

[Steve_S]

That high pitched sound is Normal and while not very loud it can be annoying. I actually do not hear it with my boxes unless I open the lids.
Online docs SUCK ! DeliGreen could certainly do better on that point without a doubt.
A respectable Discharge/Charge cycle and let it sit for a bit and the balancer will do it's job. Given a few days things will settle and even up better.
I have the older models without BlueTooth interface and they have now released one with an Interface. That is one functional feature I wish I had with mine BUT luckily, because I use Charger BMS', I can still see cell levels and activity.

 

[Horsefly]

If your usage exceeds 2A, they won't be able to keep up.

Hmmm. Not sure I understand this statement. Are you saying if the required balance current is more than 2A?

I have the older models without BlueTooth interface and they have now released one with an Interface.

They have one with Bluetooth?! Ugh. I would have bought that instead. The Bluetooth on the Overkill BMS shows me the battery voltage, which I guess is good enough. I've disabled the balancing on the BMS, and a Bluetooth from the QNBBM would (I assume) show me when it is balancing and the to/from cells.

 

[Steve_S]

The BT model of QNBBM's is "Fresh" so info is sparse.

 

[Horsefly]

They will attempt to balance at all times.

Hey @snoobler (and @Steve_S) I wanted to confirm this (and some other things):

1. The QNBBM doesn't know know if the pack is charging, discharging, or neither, so it will attempt to balance between the highest and the lowest cell at all times?
2. Lacking any documentation I searched on-line and can't find what the trigger voltage is. I.e., how out of balance do two cells need to be for the QNBBM to kick in?

I definitely have a bad cell. With the QNBBM disconnected the one cell dropped down to below 3V with no loads. The other cells remained about 3.3V. When attempting to charge the pack the BMS triggers on HVD before the suspect cell gets above 3.4V. With the QNBBM connected everything works much better. With the pack sitting quiet, they all balance to within 7mV overnight. When charging the bad cell does still cause a problem, but I can charge to a higher pack voltage than before.

 

[snoobler]

1. Yes.
2. Manuals on this page:

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10mV

You're describing a failed cell with excessive self-discharge possibly from a partial short. It should be removed from service.

 

[Horsefly]

1. Yes.
2. Manuals on this page:

Affordable Electric Vehicle Batteries & Components from Electric Car Parts Company

Electric Car Parts Company is your one-stop-shop for affordable electric vehicle parts and components including batteries. Shop our selection and order now!

www.electriccarpartscompany.com

10mV

You're describing a failed cell with excessive self-discharge possibly from a partial short. It should be removed from service.

Thanks for the link to the manual. Looks short, but maybe I don't need much.

I ordered a replacement cell as soon as I saw what it did. It is supposed to arrive mid next week. Different branding, but same exact Ah rating and physical size, so I'm hopeful I can drop it in as a replacement.

 

[Horsefly]

Ok, so I think I have a couple of questions for QNBBM experts (@snoobler and @Steve_S, but others as well):

1. I've got three items that will connect via balance leads to each cell. I'm thinking of maybe consolidating the three into once balance lead to each cell, and have a small hobby board that combines three separate devices. So the three devices (BMS, QNBBM, and a hobby charger that won't normally be connected) into one. This seems like a logical thing to do, but I don't see comments about it. Is there anything wrong?
2. Of the three the only one that is doing more than a voltage sense on the balance leads is the QNBBM, since it is actually inserting / drawing off some current through the balance leads. Should I be using larger wires because of that? That is, should be leads from the hobby board to the cells be something more like AWG18 instead of the AWG22 (or even AWG26) I would use for the other devices?

On a separate note: The cell that I thought was bad has been performing really well in my charge and discharge tests since I put in the QNBBM. Recall I mentioned that when I checked one morning that cell had gone below 3V while the others remained more like 3.3V, so I figured that cell was shot somehow. I ordered a new cell, but since then the QNBBM showed up and I've been doing several charges and discharges of the pack. It seems like all is well. The pack capacity is pretty much what I would expect (a little less than the spec).

I had earlier had a hobby charnger (iSDT Q8) hooked up to - but not powered - the pack. I'm kinda wondering of it may have done something to cause that one cell to look bad. Otherwise, I don't see how this one cell was bad and now is good.

Of course, I'm yet to pull the one cell and do a capacity test on it, which I suppose I should.

 

[snoobler]

1. The farther away the BMS lead gets from the battery, and the closer to another source (balancer), the less accurate it will be. It won't be a lot, but I don't like it.

2. I would be fine with 24awg. They don't move that much current most of the time.

 

[Steve_S]

I suppose you can do multiple devices but KISS applied is best honestly, the least stuff there the less to have issues with.
I used 12g wire of equal length from QNBBM-8S to cells. BMS wire harness is wired to the QNBBM terminal block as shown below.
I am using Chargery BMS8T's so that gives me displays on cell etc. I am absolutely NOT a fan of having multiple things attached to the cell terminals as such.. I am actually pondering drilling & taping the BusBars for a small screw and installing the LEADS to them that way as opposed to using the cell terminal, this method seems to be gaining popularity with positive results.

Now I have seen people use MOLEX Connectors to bring the BMS & Balancer wires together and then out to the cells from there. Alternatively, others have Fused it using a Fuse Block also shown, so QNBBM, BMS to one side through the fuse to cell.
The really tricky part (PITA Factor) is to make sure the connections are 100%

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Hope it helps, Good Luck.