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REC and WS500 User Forum

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REC Q incorrect (high) Voltage sense on most positive cell (Cell 8)


I recently received my REC Q from you guys.  Looks great! I'm in the process of testing it in advance of installing it on my cells.  I'm seeing a voltage sensing anomaly on what would be cell 8.  I have a full writeup of the issue here:


I've also emailed REC directly but haven't heard back from them yet.


Hey Nate, nice setup you have there!

I went through your blog findings and we are going to have to punt this one back to REC but I suspect it's a relativity issue(resistor impedance vs internal circuit impedance).  If I were to guess I would think that the final cell analog input has a slightly different internal impedance, possibly by design and that when connected to an actual battery it becomes inconsequential, but with just a 2.4k ohm resistor it shows up.

I am going to include Tine, the REC guru, in this thread and he should be able to clear it up.


@rick_tech_support, thanks!

Primoz at REC got back to me in the meantime with a suggestion that fixed the issue.  Essentially the resistances on the "battery simulator" were too high.  @tine, nothing more needed!

Updated write-up: github.com/natecostello/van_two_point_oh/blob/master/blog/2021-4-10/REC-Q-CAN-Comms-Voltage-Sense-Anomaly.md

Thanks all for the prompt response and effective solution.

It looks like we were on the right track, because the resistance of each voltage divider resistor was so high they were affected by the internal impedance of the analog input circuitry.

From Tine:  He should use 180-390 Ohm and it will work OK.

For those interested in pre-testing their configuration while waiting for their cells to arrive this is a great idea!



natecostello has reacted to this post.

@tine @rick_tech_support any issue with using something as low as 56 Ohm?  I have a bunch laying around and was going to use them?

That's likely a bit low and may generate a bit of heat.  If you have lots, just put them in series in sets of 4 per drop, for a total of 32 (4x56 ohm= 224 ohms).  Right in the range that Tine suggests

Just a note to all.  The resistor test battery simulator described above will work with the Q Series, but the 12V Active BMS uses active cell balancing and during startup it first tests this function.  If there is no actual cell present to test, it will generate an error and not complete its startup.

In short, you can use a resistor divider circuit to test the Q Series but not the ABMS.