simonmtl avatar image
simonmtl asked

100/20 goes thru charging cycles many times in 1 day !?


Just got my installation done yesterday! Fun to look at and check the statistic on the app :)

My system is 100/20 mppt, 2 x 225 ah 6v, 295w solar panel and bmv712 installed in a sprinter van

Yesterday got the charger to charge and everything looked fine, but this morning I went to work parked the van under the sun, it was in bulk mode at that time. 8 hours later, after work I come back to the van, check the mppt status light it shows it’s in absorption, which I though was normal. Then I check the app and it shows it did went thru the float mode for a part of the day...

So I drive back home, once there it was now in float mode, thought it was weird. Went inside my house get a snack, and now it’s back in bulk mode

Is that normal?

I thought the cycles was to happen one after the other and it was not going to cycles thru them. Maybe I’m confused...

Just to make it clear, I have a 12v refrigerator hooked on the system, duty cycle is about 15minutes and it roughly draw 50w while on

Also I have checked the plates they look clean without sulfatation

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2 Answers
Mark avatar image
Mark answered ·

What do you have your float voltage set to & during that time was the float voltage able to be sustained or did it drop?

Depending on which firmware you are running in your MPPT, the 're-bulk' voltage will be either 13.7v or 13.4v - so if the float setpoint voltage happens to be set below this voltage or if the battery voltage drops below the 're-bulk' voltage (due to loads + lack of solar power) then it will trigger a new charge cycle starting with the bulk phase again.

If this happens late in the day it will most probably never reach absorption before dusk & finish the day in bulk phase.

In the upcoming firmware release, it is intended for the 're-bulk' voltage to become user configurable.

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simonmtl avatar image simonmtl commented ·

Ok! I didn’t know it could do a rebulk, I thought charge mode were happening one after the other with no coming back, but it makes sense that it can do rebulk

So my batterie are Magnacharge GC225 which are six volt and from what I understood is a de-branded Trojan T-105

My firmware is the latest version, so I don’t know what is the rebulk voltage is!?

My setting is

Abs 14.8v

Max abs time 6hrs

Float 13.20v (might be too low)

Eq 15.5v

Those are data I took from a T-105 data sheet but I found another one on the web for the t-105 that has different float and eq (13.50 and 16.20). I didn’t use them cause I thought maybe that was for a newer version of the T-105 and I wanted to play safe using lower number. I don’t want my batteries to explode :/

I will be contacting Magnacharge directly to have real spec from them since I can’t find it on their website :(

In the meantime, should I increase float?

Any danger if I put numbers too high??


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Mark avatar image Mark ♦♦ simonmtl commented ·

See your new post for my comments regarding MPPT FW rev & re-bulk voltage.

I prefer not to advise directly on what charge voltages you should use (that's up to you) - but based on the T105 data sheet 13.5v is the recommended float voltage & does not seem excessive to me.

Going too high with the absorption voltage is much more of an concern as it will cause rapid gassing to occur (~14.8v is probably on the high end, but if its recommended by the battery manufacturer should be OK).

Attached below is some very good & interesting information charge voltages & gassing/water consumption with wet lead acid batteries - the extract is from the free Victron Energy book 'Energy Unlimited';

But I would also recommend to use automatic temperature compensation with your MPPT - otherwise you really should keep a constant eye on battery temperature and MANUALLY keep adjusting the charge voltages as required per the battery manufacturers specifications;

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simonmtl avatar image
simonmtl answered ·

thanks again.

so I got the data sheet from the manufacturer today, good news is that my setting was correct

now, i think I will be contacting my distributor to have some advice over the phone..

trojan-gc-225-1.png (359.3 KiB)
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