I have a bmv-712 but it does not show any positive readings when charging the battery. It displays negative readings but I can’t figure out why it does not display positive readings when charging.
Any tips???
asked
BMV-712 Input Detection??
It turns out I had the solar charger connected to the “battery” side of the shunt rather than the “load” side.
This fixed the problem.
I appreciate everyone’s quick response.
Thank you!
Glad you were able to get it working again! The great things about these devices is how simple they are; there are only so many things that can possibly go wrong with them :-D
Thanks! So now my question is why does the battery voltage readout drop when I’m using energy... for example, when I have things plugged in or lights turned on. Sometimes the voltage drops to 11.8V even when I know the battery is fully charged. When I turn everything off then the voltage readout climbs back up to 13-14v.
Yes, this is normal; your loads are of course consuming energy, so you'll see a voltage drop when you switch them on and that voltage will steadily decrease as you leave them on and consume the energy stored in your batteries. The drop to 11.8 is a bit extreme; that must be a big load! Keep in mind that you may be starting with a fully charged battery, but as soon as you apply a load it's technically not fully charged anymore, because you have now consumed some of the stored energy.
As you increase the Ah capacity of your battery bank, you'll see less of a voltage drop when you switch on your loads, as the load is spread across more capacity; furthermore, different battery chemistry = different behavior when under load. A flooded battery behaves very differently under load than a lithium battery, for instance.
The reason the voltage "comes back" when you switch off your loads is slightly complex to explain without you having a prior understanding of the way a battery actually works... I'd suggest some internet research and possibly YouTube surfing to get a grasp the fundamental chemical operation of a battery; until then, suffice to say that a fully charged 12v battery typically has a resting voltage of around 12.8v; this will be higher immediately after charging (13-14v) but will drop to the resting voltage when a load is applied; thereafter, the more of your battery capacity that you use, the lower the voltage will show; furthermore a battery under active load will show a lower voltage than its resting voltage because, simply put, it's not resting. When the load is removed, the voltage reading will return to its resting voltage minus the capacity that was used to run the load.
Your charger should be charging at around 14v, so if you're actively charging or have recently completed a charge cycle, I'm not surprised you're seeing that voltage. If you're not actively charging or very recently completed a charge cycle, however, and you're still seeing the voltage climb back to anywhere near 14v after you've had a load on the battery, then you're very possibly over-charging your battery, which is extremely bad for it. I definitely suggest that you consult your battery manufacturer to establish the recommended charging voltage for your particular battery(s) and then review the charge profile settings on your charger to ensure that you have the appropriate charge profile set.
This is gold. Thank you for the info!
The 11.8v was a reciprocating saw running off of my inverter.
I think you may be right about it climbing back up to only 12.8v.
I have seen my battery voltage as high as 14.4v during charging...but I assumed my charge controller would prevent over charging.
I will look further into the possibility of overcharging.
Again I very much appreciate all the valuable information!
Yes, your charge controller running at 14.4 is perfectly acceptable for most batteries except AGM and Gel. Most other types of lead-acid batteries or lithiums, however, will be perfectly happy at 14.4 charging voltage.
Another note is that yes, reciprocating saws and other capacitive loads have a major startup draw, then that will taper off once they're fully running. Furthermore, the inverter itself is a capacitive load, and simply turning it on will cause a semi-momentary voltage dip.
The SOC will even tell me my battery is charged but the voltage readout drops really low.
@Darcy Martin, 99.8% of the time that a BMV isn't showing charge it's because your charger isn't hooked to it. Keep in mind, as stated in the instructions, that one wire should be connected to your battery negative, and that wire goes to the "battery" side of the shunt. ALL other system negatives must be connected to the "load" side of the shunt. That includes chargers, component negatives, chassis grounds, etc. The BMV uses the negative shunt to measure all current in/out of the system, so if your charger is hooked directly to the battery, the BMV can't see it.
Make sure that nothing other than the "battery" side of your shunt is connected to your battery negative post; if you're still having issues after that, post some pictures of your setup and we'll figure it out from there.
No, I'm not trying to be a jerk...
Okay, I've never seen a BMV-712 firsthand, but this sounds like some basic DC voltage troubleshooting. First off, I'll assume that you aren't expecting to see a + symbol to the left of the numeric readout. What is happening when you see the negative (-) readings? Are all the necessary wires connected to the shunt properly? If in doubt, double and triple-check. Check the continuity of your cabling. You can trust, but you must verify. Are you seeing any voltage increases during the charge phases?
Has the unit been synchronized? This is going to be difficult to troubleshoot without more information. What kind of arrangement is this? Solar/generator/alternator involved? We need a wiring diagram. You need to be the eyes for the forum. The more accurate details you can provide, the better. If in doubt, go look, and take some pictures for us.
packrat
Something else came to mind. Did you need to, or have you calibrated the zero current setting? Refer to the manual for a better explanation than I can provide at the moment.
packrat
i Will look into this as well as I have not done a zero calibration.
