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FarmerJake · 05-05-2021, 05:42 AM

I’ve got a 100 watt solar panel. I also have a BMS that is shunted across the battery, but noticed that it normally shows less than 1 amp of current flowing to the battery while the sun is shining. At one point yesterday, I checked my solar controller and it showed the panel was producing 3.5 amps, but the BMS was reading around 0.7 amps (and the batteries are not fully charged). As a test, I plugged into shore power and the BMS immediately shot up to around 8amps and then quickly settled down to ~4amps.

So, the question is: if my solar controller is showing 3.5amps flowing in, shouldn’t most of that be going to charge the battery? Am I missing something?

Zanzabar · 05-05-2021, 05:52 AM

Try adjusting the charge profile of your controller, might not be set up correctly fir your battery type. Sounds like it is in its 'float' stage.

FarmerJake · 05-05-2021, 05:59 AM

Thanks for the suggestion. I know it’s set for a flooded battery, which is correct. But I’ll take a look at the manual to see if there is some other setting that might be incorrect.

Mark_K5LXP · 05-05-2021, 06:44 AM

If the solar controller is indicating one level of current and the BMS something else, then that difference current is going somewhere.

Mark B.
Albuquerque, NM

FarmerJake · 05-05-2021, 06:53 AM

I found my answer in the solar controller manual. In the “normal” mode of operation it uses a float charge of 13.7V and limits the current to 1Amp. It charges in bulk mode for 30 minutes every morning (or for two hours if the battery is below 12.3V). I can also select a “boost” which will do a bulk charge at 14.4V for 30 minutes....which they recommend you do at the end of the day, which I find interesting because I’m not sure there would be enough sunlight to make that effective!

Now the next question. If I draw my batteries down to, say, 12.4V overnight. The entire next day (with the exception of the 30 minutes of bulk) the batteries will only be receiving less than 1A. So, at the end of the day, they probably won’t be fully charged, even though there may have been sufficient sun to do so! I don’t get it! I was also considering adding another solar panel so we can boondock longer, but now I’m wondering what that will buy me if the batteries will only receive a maximum of 1A anyway!

Rumline · 05-05-2021, 07:15 AM

That doesn't sound like a terribly useful solar charge controller. What is the make/model?

FarmerJake · 05-05-2021, 07:31 AM

Go Power! Model: GP-PWM-30-UL

Mark_K5LXP · 05-06-2021, 06:13 AM

Looking through the manual it's one of those kind of controllers that operates by assumption. Rather than have the user set the bank size, mode thresholds and times, it just sets the charge modes based on battery voltage and preset times. When the stars align and you hold your mouth right, this setup can probably work OK.

I don't see anywhere there's user adjustable settings other than battery type. It does have the "boost" which I would probably be using all the time, and the auto EQ feature is nice. It is what it is- a "hands off" simple, basic controller for light duty installations. If you find that over time it's chronically undercharging your batteries or doesn't utilize your panel capacity the way you'd expect or need, the only repair is by replacement. Since you already own it, let it ride for a while and see how it does. Maybe it's good enough for what you need.

Mark B.
Albuquerque, NM

astrocamper · 05-06-2021, 09:36 AM

Battery monitors with shunts need to be periodically synchronized. If you plug in so you batteries are being charged by the converter you can watch the voltage of the batteries reach their peak and the amperage flowing into the batteries drop off until you are effectively trickle charging. At that time synchronize your battery monitor at 100%.

Your solar output will only reach the peak when the battery charging and other current draw is equal or great than what is being produced by your 100 watt panel. Turn on some loads at about 1PM on a fully sunny day and see how much current is coming from your solar charge controller.

Rumline · 05-06-2021, 01:52 PM

Considering that a full-featured Victron solar charge controller is available for less money, I would never recommend this particular model. I never really had an opinion of Go Power before but this makes me highly suspicious of their products.

FarmerJake, are you still within the return period for this?

Rumline · 05-06-2021, 02:00 PM

Quote:

Originally Posted by FarmerJake

So, the question is: if my solar controller is showing 3.5amps flowing in, shouldn’t most of that be going to charge the battery? Am I missing something?

This is a separate issue. If you have any loads active, like lights etc, then the power from the solar panel can flow to those loads rather than into the battery. Even if everything is off you could still have parasitic drain of an amp or two from carbon monoxide detectors, etc that you might not be able to turn off without a disconnect switch or pulling a fuse. That's worth investigating anyway, just so you know what draws power all the time in your rig.

astrocamper · 05-06-2021, 03:26 PM

One of the things I did after buying my VE BMV-712 is to turn off everything and see what the base parasitic load was. Then I turned on one item for a few minutes to see what additional load each device took to run. This included turning on the big inverter/charger and seeing what the standby load was and then turning on the big loads such as microwave, toaster, blender, air conditioner on at a time.

FarmerJake · 05-06-2021, 08:08 PM

Thanks for all of the replies.

I spoke to someone in tech support. I was told it was probably in float mode since the batteries were “nearly” full. According to my BMS, the batteries were at 140-145amp-hrs (capacity is 150). So yes, they were nearly full. But, I still think they should be charging at a greater rate, until they get “very” close t9 full.

I have it plugged into shore power now, so I’ll resynchronize my BMS in the morning. We’re going on a several week trip starting tomorrow and will be boondocking for some parts of the trip. This will give me a good opportunity to see exactly what is going on under different conditions. I’ll take some notes each day, because I’ll never be able to remember it all!

Mark_K5LXP · 05-07-2021, 06:39 AM

Yeah, I'm not impressed. "Float" is when the batteries have completed an absorption phase, with this controller there's no distinction between that and just coming off of bulk phase. So there's quite a disparity there in terms of state of charge and if you cycled your batteries like this consistently they'd be chronically undercharged. It's my guess the protocol they've adopted with this thing is to err on the very conservative side. The "boost" button could mitigate that somewhat, so I guess the jury is out until you get some runtime on it and see how things work out.

Mark B.
Albuquerque, NM