ajbremer avatar image
ajbremer asked

Victron MPPT 100/50: Doesn't go into Float...

I have the Victron MPPT 100/50. It's a 12 volt system hooked up to solar panels and eight 6 volt batteries. I'm inputting over 600 watts from the panels. The battery section of my SmartSolar app I use on my iPhone says my voltage is over 14 volts but I still see that it's in the Bulk mode. I'm concerned that too many charging volts are going into the batteries because the Victron hasn't switched to Float mode. Does it take awhile to go into Float? Here's what I have in my settings:

Battery Voltage: 12V

Max Charge Current: 50A

Charger enabled: Yes (on)

Battery Preset: User Defined

Absorption Voltage: 14.40V

Float Voltage: 13.50V

Equalization Voltage: 16.20V

Automatic Equalization: Disabled

If I see a voltage of like 14.5 and it's still in Bulk mode, can that be dangerous? Thanks!

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1 Answer
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snoobler answered ·

The danger associated with 14.50 depends on your batteries. It may or may not be harmful.

I'm assuming these are lead-acid.

Lead-acid charging requires the absorption voltage be held for a period of time. It depends on the absorption duration setting you have on the expert screen. For batteries discharged a significant amount, the absorption period is typically about 2 hours. If the discharge is shallow, and you're using the adaptive algorithm, it will be shorter. Here's what a charge profile looks like:


A = bulk, below the absorption voltage. Charger will send however many amps it can.

B = absorption, holds the voltage and tapers the current.

C = Float, occurs based on the rules for terminating the absorption phase.

A common criterion for dropping to float is a tail current. Using your charger numbers, a 100Ah lead acid battery held at 14.40V until the current drops to 2A (2% of capacity) is fully charged. Different manufacturers may state different criteria, but it's typically 1-4%.

You said "over 14 volts," but you didn't say if it was over 14.40. If it's not to 14.40V, it's in the bulk phase. If it's AT 14.40V, it needs to stay there long enough to get fully charged. That depends on the output of the charger and the capacity of the battery.

Note that few voltage measuring devices are exactly accurate. I would not be concerned by voltage differences ±0.05V or so.

Also note that properly charging lead acid requires something called temperature compensation. Lead acid voltage values are typically for 25°C conditions. If it's colder, the charge voltage should be higher. If it's higher, the charge voltage should be lower.

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