Bill avatar image
Bill asked

My reseller is telling me that if I hookup a BMV 712 to multiple controllers they will stay syncronised?

My two controllers charging the same battery bank are setup exactly the same but one will be in bulk the other float very often. Is my reseller correct about the BMV keeping them working identically? I plan on adding LiFePo4 batteries and want to keep them in pristine shape using two 100/50's, with 640w on each controller. -Bill

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2 Answers
Justin Cook avatar image
Justin Cook answered ·

@bigbillsd, that's not exactly accurate; to be fair, you absolutely and 100% should have a BMV on your system so that you know what's going on with your battery bank, but it's not (currently) going to help synchronize your controllers.

The reason that you're seeing the "one in bulk and the other in float" so frequently is because one of the controllers is turning on earlier than the other; the first controller wakes up, decides at that moment -based on current battery voltage- how long its absorption cycle is going to be, and starts charging your batteries. The second controller wakes up a little later (partially because the first is now raising the battery voltage, which affects the batt voltage +>5v initialization parameter of the controller) and since it wakes up later and sees a higher battery voltage, it decides how long its absorption cycle will be, and that will be a much shorter period of time than the first controller because, again, it's seeing a higher voltage than the first one did.

Basically, the first controller to wake up will spend the longest in bulk and absorption. It's not a problem, really, because you can only harvest as much power as your batteries will take anyway, and I'm sure you're still getting a full charge every day. It's just a little off-putting on the surface because you expect them to be operating in sync... but, by the very principles by which they work, it's virtually impossible for the two controllers to ever be perfectly in sync.

That being said, two things:

1: You can get a lot of benefit from having a BMV, but syncing the two controllers is not one of them; yes, with the BMV you can create a VE.Smart Network between your BMV and both controllers, but this is not currently going to affect the actual charging rates or timings of them.

2: A firmware update is in the works that should let paralleled MPPTs share more information amongst themselves to more efficiently charge a single bank between two or more controllers. So it might be said that your reseller is preparing you for the future, but if you buy one today and install it, you should not currently expect to see any marked difference in behavior.

Still, however, I'll say again that you absolutely should have a BMV on your system, particularly to help monitor and protect your lithiums once you get them.

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Bill avatar image
Bill answered ·

Understood, I am going to swap out my Trimetric for a BMV real quick to gain the extra Bluetooth range.

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