question

Laura Hoey avatar image
Laura Hoey asked

BMV-712 always reads "Infinity"

I connected the BMV-712 to a new 170ah LFP battery yesterday (BMV is about 1-year old, and worked last year on a Lead Acid set-up). Although it initially indicated "10d 10h" when the battery was disconnected from shore power, now it reads "Infinity". I have done a factory reset, but nothing changed. I disconnected the UTP cable, but nothing changed. The battery monitor also consistently reads .11v lower than a direct read at the battery (I had this same problem with the Lead Acid set-up). For example, in the attached image the reading is 13.69, but a direct read at the battery is 13.8. I also wonder why "Starter Battery" indicates a voltage amount when no starter battery is connected?

Are there any tricks I can try, or is it possible I have a bad monitor? Maybe a bad UTP? Please forgive the messiness of my set-up right now, it will get cleaned up once I isolate the problem.

BMV Battery Monitor
img-3336.png (187.6 KiB)
img-3335.png (162.1 KiB)
img-3334.png (176.1 KiB)
img-3333.jpg (108.9 KiB)
img-3332.jpg (139.2 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
wkirby avatar image
wkirby answered ·

Is the battery fully charged and then synchronized? If it is not synchronized, it does not know how full the battery is and therefore doesn't know how much time to go. So it shows infinity.
Also ensure that you have amended the battery capacity setting on the BMV. The SOC calculations rely on knowing the correct battery capacity.

For the Voltage discrepancy, remove the fuse from the inline fuse holder along the red wire. If you can read it's rating, it's probably 100mA. This fuse has an impedance of about 6 Ohms. This calculates to a Voltage drop of about the amount that you are seeing.
Set that fuse aside and install a 1A fuse. The Voltage readings will be super.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Laura Hoey avatar image Laura Hoey commented ·

Thanks for your response, especially the inline fuse question (that was a real annoyance). I synced the battery last night when the voltage read 14.57v, which I consider fully charged for a LFP battery. It still continued to show Infinity. I may try bypassing the monitor all together, bring it up to full charge and then reconnect the monitor to see what happens.

0 Likes 0 ·
bora avatar image
bora answered ·

When I installed my BMV-712 I had the same problem, turned out I had the shunt wired up wrong. So a reversal of the -VE leads sorted the problem.

7 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Laura Hoey avatar image Laura Hoey commented ·

Thanks for your response. That's interesting.... I only have one lead connected, and it's to the B1 slot (closest to the UTP connection). If I try B2 I get no power. I may have to just ignore it, I never took the information that seriously anyway.

0 Likes 0 ·
Mark avatar image Mark ♦♦ Laura Hoey commented ·

@Bora is talking about the main NEGATIVE cable connected to the large M10 bolts on the shunt, not the positive cable connected to B1.

It's essential that the side of the shunt labeled as 'Battery Only' is connected directly to the battery negate terminal & that ALL loads & charge sources are connected to the other end labeled as 'Load / Charger'.

0 Likes 0 ·
Laura Hoey avatar image Laura Hoey Mark ♦♦ commented ·

I see, thanks for that clarification. Unfortunately (for me finding a solution), the wiring between the shunt and battery is correct. I'm beginning to wonder if the UTP cable became corrupted in some way.

Thanks for your input.

0 Likes 0 ·
Show more comments