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Old 24-10-2016, 02:20   #1
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solar charging confusion

I have 4 X 140W (560W) solar panels wired through a Midnite solar MPPT charger to 675ah of wet cell Trojan batteries(6 batteries , each 2 in series and then parallel).

My questions is..... whenever the sun is out at mid day I always see about 180 to 220W going into the batteries (bulk mode). when the charge reaches absorption mode I sometimes see about 300 to 400W, and if I equalize its 400-500W.

In bulk mode how come im missing out on those Watts going into the batteries (200W instead of about 500W)?

is that because that's as much as the battery bank would accept? would I benefit of accepting more charge if I increase the battery bank capacity?

thanks,
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Old 24-10-2016, 03:29   #2
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Re: solar charging confusion

Welcome to the forum Adib.

Your problem is a puzzle.

In the same conditions the solar regulator should be putting out more current in bulk than in absorption mode. By definition the regulator is throwing away some power in absorption mode to keep the battery voltage acceptable.

If the conditions are poor (say the sun direction is such that there is a large shadow on the panels) then the panel output will be less and the regulator will need longer in bulk before the batteries are charged enough to switch to adsorption mode. I suspect this is what is happening and causing you to correlate bulk charging with a lower output.

Normally the bulk voltage is automatically the same as the absorption voltage. Some regulators let you set the bulk voltage independently of the absorption voltage. Check the bulk voltage has not been inadvertently set lower than the absorption voltage. Other than that It is hard to imagine a controller fault that would lead to your symptoms.
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Old 24-10-2016, 04:52   #3
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Re: solar charging confusion

Greetings and welcome aboard the CF, adib.
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Old 24-10-2016, 12:00   #4
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Re: solar charging confusion

Shunt regulator???
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Old 24-10-2016, 12:21   #5
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Re: solar charging confusion

3 things I can think of (none may be right)

1) hot panels. Bright sun heats panels. Hot panels less efficient. Highest efficiency bright sun on cold panels (like when does that happen?)
2)watts error instead of Amps, or the meter algorithm is wrong
3)batteries are low at midday so low voltage makes watts/amps appear low
4) bad connection gets better with heat?
5) your "always" and your "sometimes" are delusions. Write down times and watts/amps.

I think its 1 &3 combined.
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Old 24-10-2016, 19:01   #6
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Re: solar charging confusion

when your solar first start's up in the morning the sun is probably pretty low in the sky and a later in absorb the sun is probably higher.

bulk or absorb will each max out the current as needed.

what is your battery voltage during those cases?
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Old 25-10-2016, 01:22   #7
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Re: solar charging confusion

Thanks guys for the info, I will try to make things more clear.

1. I made sure that the bulk and absorption settings are the same.

2. what I have described in my first post is considering the same conditions, sunny day between 11am to 3 pm, similar partial shading(backstay) as usual, same behavior for a year , noticed every day, this has been going on since I first installed the system and it has been working in the same way for a year now, I just always wondered why I wasn't getting that proper charge of about 350-450 watts during the bulk stage.

3. I have checked all the connections a few times and nothing wrong there.

for example on a normal sunny day:

Just as the sun is rising my battery voltage is about 12.4 V, and since the sun is very low I am only seeing about 5 amps, 62watts, Bulk stage,which I expect.

by about 11 am, my battery is about 13.2 V , I am getting 16amps,211watts, Bulk,on average.

It will continue that way for a few hours while the battery voltage creeps higher to about 13.8V , still showing about 16amps, 220W, bulk

when the battery voltage reaches about 14.4V or higher at around 2pm, the mppt switches to absorption mode , then I start getting more amps suddenly, about 25amps, and reading about 360W or more.

this sudden increase in performance of the charging system only happens after the batteries have been charging for a while and the mppt switches from bulk to absorption.

shouldn't I be getting the same type of performance of about 25 amps and 360W earlier on in the day when the sun is high and its in Bulk stage around 12 noon?

I always thought is was a case of what MarkJ mentioned in his Third point but thought I would make sure with you guys.
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Old 25-10-2016, 02:05   #8
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Re: solar charging confusion

What you are describing should not happen. It is very hard to imagine these sort of symptoms from a simple fault like a bad connection.

I think it must be an internal fault to the regulator (perhaps not tracking properly in bulk mode). Often these sort of faults are a software rather than hardware problem. Try a system reset (this will return all settings to default so record all the voltages etc so you can put them back in). On some of the Midnite controllers you can do a software update and this might clear the error. Otherwise it is back to the factory.

Ring Midnite first and see if they have any suggestions.

Let us know the outcome.
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Old 26-10-2016, 17:24   #9
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Re: solar charging confusion

I agree. switching from bulk to absorb at 14.4v is totally normal. but the lesser amps in bulk is unexplained. asumming you have simular sun is probably a controller issue
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Old 26-10-2016, 19:08   #10
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Re: solar charging confusion

How are you measuring your current? You have quite a large bank and it seems to be charging. I wonder if you have been mislead by your instruments.

Or, you have a controller problem...
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Old 26-10-2016, 20:59   #11
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Re: solar charging confusion

Fast reality check: Bypass the MPPT controller, disconnect it and anything else from the batteries, except stuff that really shouldn't matter, like the inactive bilge pump. If there's a fridge/freezer or any possible heavy load, make sure they are all OFF. If there's anything like an Echocharger, turn it off also. Now use a voltmeter and an ammeter (which may mean spending $50-100 on a clamp-on DC ammeter or else installing a shunt) and read how many volts and amps you are actually seeing when JUST the solar array is connected to JUST the battery bank. In theory, I'd expect to see the rated output, which would pretty much match the max you've been seeing in the "wrong" modes, give or take whatever the battery's SOC is allowing. What you are doing is confirming that the solar array IS putting out full output, and once that is confirmed, the only other culprit (unless you're hiding something(G) is the MPPT controller. Go over the reset and programming with Midnite, make Real Damned Sure you have it set right because I've seen manuals where pictures were upside down and switches were numbered backwards from reality. I'm betting that either you have a configuration problem, or a seriously sick controller, in which case it needs to go out for service. (And you may have a year of warranty extension if you bought it with a credit card, keep that in mind.) Bulk charge certainly should be using ALL the power the solar array can put out, subject only to the acceptance limits of the battery bank. Which simply aren't going to be HIGHER as the batteries get more fully charged.
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