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NeverForever avatar image

Can the BMV-702 Limit Charging Current?

Originally, I was having a problem that was well explained in this forum, i.e. SOC = 100%, despite battery being at 12.5v. So, I changed the "charged voltage" setting from default 13.2 to 14.1, since I'm usually solar charging. But the SOC still reads 100% at 12.6V to 12.8V. Now, since I'm concerned about my battery health, I am trying to fully recharge with a generator. However, it seems that the system thinks it's at 100%, float stage, so only draws 5 amps (it would normally draw 40-50 amps off this Honda 2000W). My battery bank is two 8D batteries, so 5 amps will take forever. Or is something else wrong?

BMV Battery Monitorbattery chargingSOC
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3 Answers
NeverForever avatar image

@MrT: Thank you both. Apologies for my suboptimal understanding of these systems. There is a BlueSolar charge controller MPPT 100/30 for the solar, with a Mastervolt Mass Combi to charge the batteries. In case it could be relevant, I changed out the existing standard batteries for Lifeline GPL-8DL 4 months ago.

My issue is that the BMV continues to show 98-100% SOC, seemingly regardless of the actual charge. BMV settings are battery capacity = 510 ah, charged voltage = 14.1, set tail current is set at 1% because of the 510 capacity, but I don't see a setting for float voltage. When I attach a generator via the shore power input, the batteries only charge at 5 amps. Of course, while charging, the BMV shows the charge as 14.1-14.3 volts. After 12 hours of charging at 4-5 amps, as soon as the generator is disconnected, the BMV shows the battery charge as 12.7 volts. What am I missing? What could be causing the charge to be limited to 5 amps, when the batteries are at 12.5-12.8v and "charged voltage" is set to 14.1v?

Thanks again!

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Justin Cook - Bay Marine Supply USA avatar image

@NeverForever, something else is indeed very wrong. Either your voltage readings are wrong, or something is amiss in your charger, or something is amiss in your system wiring... under no circumstances, however, can a BMV-7xx limit charging or discharging of your battery bank in any way, shape or form.

I strongly encourage you to take your entire system to a qualified and experienced DC systems installer to fully inspect the whole installation and identify and fix the actual problem(s) that are present on the system.

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MrT avatar image

Your BMV doesn't limit or control anything … it is just a measurement device. You haven't said what charger you are using with the generator but if it is only charging at 5amps, it suggests the battery is near fully charged. If you fully charge with a proper multi-stage charger (configured for the chemistry of your batteries), sync your BMV … and it has been set with correct parameters ie battery capacity, charge voltage, float voltage etc .. then the BMV should approximate you battery SOC

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Thank you both. Apologies for my suboptimal understanding of these systems. There is a BlueSolar charge controller MPPT 100/30 for the solar, with a Mastervolt Mass Combi to charge the batteries. In case it could be relevant, I changed out the existing standard batteries for Lifeline GPL-8DL 4 months ago.

My issue is that the BMV continues to show 98-100% SOC, seemingly regardless of the actual charge. BMV settings are battery capacity = 510 ah, charged voltage = 14.1, set tail current is set at 1% because of the 510 capacity, but I don't see a setting for float voltage. When I attach a generator via the shore power input, the batteries only charge at 5 amps. Of course, while charging, the BMV shows the charge as 14.1-14.3 volts. After 12 hours of charging at 4-5 amps, as soon as the generator is disconnected, the BMV shows the battery charge as 12.7 volts. What am I missing? What could be causing the charge to be limited to 5 amps, when the batteries are at 12.5-12.8v and "charged voltage" is set to 14.1v?

Thanks again

If the batteries are only absorbing 5A at 14.3V, then they are "full". If they immediately fall back to 12.5V on taking off the charge, then one of those "full" batteries is actually "failed", and can't actually absorb a meaningful charge. Or perhaps if you are lucky there is just a very poor connection somewhere.

While the battery is charging, use a multimeter and test the voltage between every point (between battery cells, battery take-offs, take-offs to DC bus, all the fuses, DC bus to charger, and any in-between) to see if there is any unusual rises, falls or inaccuracies.

Then do the same when the battery is discharging. That should begin to reveal where the problem might be.