Solar Charge Controller End Amps Base Load Considerations

[B and C]

Wish Sternwake was still around for this.

Something I have not seen addressed in solar charging is base loads connected to the battery, i.e. propane/co detectors that are always on as well as any other device that would constitute a load on the battery day and night.

I have a base load of 1.2 amps.  My charge controller is a MPPT MidNite Kid with a WhizBang Jr. and a 500 amp shunt.  I also have a Bogart Trimetric battery monitor that only shows me what is going on.

My battery negative is tied to the shunt and the other side of the shunt is chassis ground.  All my loads are on chassis ground, nothing tied directly to the battery or the load terminals of the controller.

My question is end amps.  If end amps are supposed to be 1.7(8) amps (1/2 C for my system (350AH AGM)) but I have a 1.2 amp base load, do I set end amps at 1.7 or 0.5?

I have it set at 1.7 currently and usually get to 100 % according to my Trimetric (also set at 350AH battery).  Is this optimal and way off the mark?  These are older telephone system batteries with no info on end amps.  I got them when they were 5 years old and have been using them off an on for 4 years.  I just have a gut feeling that I am under charging them.

I cannot seem to find on Google ('course I maybe I am not using the right search terms) anyone addressing this base load and end amps.

 

[John61CT]

If the AH counting SoC meters are installed and working properly

then they should only show the amps actually being accepted into the bank,

net of any loads.

350AH bank .005C endAmps is indeed 1.7-8A.

1/2C means .5C so confusing.

If you want, drop to 1A, with FLA no harm, just keep well watered.

Note worn bank may never get that low, so tweaking is fine.

Sounds to me you're not undercharging.

Can also tweak V higher.

But that first "if" above is the key, don't use chassis ground myself. . .

 

[B and C]

John, you're say the base load has no effect on end amps?

AGM batteries, not FLA

 

[B and C]

If the AH counting SoC meters are installed and working properly

then they should only show the amps actually being accepted into the bank,

net of any loads.

The Bogart is connected to the shunt according to the directions supplied by Bogart. 

The meter shows me how much I am taking from the battery after sunset or when I disconnect the panels.  This is where I get my base load from.

I can see my base load slowly disappear in the morning as the sun comes up.  Although I don't care what the meter says.  My logic says the solar controller sees the base load too as it is supplying power for it and I should set end amps lower to compensate.  I know I have it set right if there were no loads.  My question was about the base load which was not addressed AFAIK.  You seemed to talk about everything else.  Not sure what "net of any loads" is.  Call me dense if you want but I would like simple.  To put it simply, do I subtract my base load from my end amps or not?

Is there any question of how I have my loads connected?

 

[John61CT]

No.

Say your loads are pulling 3.5A, while charge source is putting out 8A.

The AH counter should show 4.5A going into the bank.

Net means after the other factors are accounted for, the final result.

 

[B and C]

OK. Seems like the going into the bank is also going into my baseload.

Have you got a reference for this or just an assumption?

 

[John61CT]

Seems like the going into the bank is also going into my baseload.

No idea what that is supposed to mean.

Part of the input goes to carry loads.

The remainder is available to be "accepted" into the bank, actual rate depends on SoC, voltage and resistance.

No "reference" needed, like saying gravity pulls toward the ground, that's just how it works.

But only with the shunt installed at that bottleneck bank location.

Put it somewhere else, and it will measure something else.

Can make up a portable ammeter / AH counter by placing Anderson plugs at various strategic spots around the system, measure just solar contribution or just the alt output, without regard to which loads it's going to.

Or just measure consumption of one circuit or one device.

In this case you're measuring what that bank is "using" as a load, pulling from the charge source.

Not sure how else to explain it. . .

 

[John61CT]

One key point is that with the charge source active nothing goes "through" the bank, that is just another load.

At higher current outputs, all the loads are serviced directly from the source.

If load currents get higher then they pull from the source and the bank, and charging stops.

Hope that helps.

 

[DLTooley]

You could disconnect some or all of your base load and observe the change.

 

[John61CT]

If the BM is just measuring bank acceptance,

and the total Loads + trailing amps is under the source output

then turning off Loads should show no change at all at the BM

 

[highdesertranger]

we need to stop using abbreviations so much. newbies have no idea what you are talking about. the first time you want to use BM write out battery monitor(BM) then in the rest of the post use BM. this is especially true with electronic posts. doing it this way helps newbies learn the lingo. this post is not trying to single John out it is meant for everybody. thanks, highdesertranger

 

[rm.w/aview]

Thanks for pointing out this incredibly annoying aspect of posting.

 

[B and C]

If the BM is just measuring bank acceptance,

and the total Loads + trailing amps is under the source output

then turning off Loads should show no change at all at the BM

The battery monitor (either charge controller or battery monitor) is NOT measuring just bank acceptance.  It is measuring what is going to the battery AND the load because all the charging/discharging goes through the shunt.  :huh:

Wow.  I think I finally got it through my pea brain.  The last part of the above sentence tells it all.  The charge goes through the shunt as a positive amount to the battery and the part going to the load is a negative amount going through the shunt in the other direction leaving whatever is left as a positive amount going to the battery.

Thanks for the discussion.  I just needed someone to talk it out with I guess.

 

[John61CT]

The battery monitor (either charge controller or battery monitor) is NOT measuring just bank acceptance.

No, these are two completely different devices, measure different things.

The CC is only measuring what it knows about, its output and maybe some loads powered from its own load terminals if any.

Unless it has its own BM+shunt add-on.

A BM measures via the shunt at the battery. Only measures what goes into (and later, out from) that battery.

The loads' energy powered by the charge source, does not go anywhere near the battery, so the BM does not measure them. You would need another ammeter / AH counter with the shunt placed at the circuit you want to measure.

> It is measuring what is going to the battery AND the load because all the charging/discharging goes through the shunt.

Yes at the SC, no for the BM.

> The charge goes through the shunt as a positive amount to the battery and the part going to the load is a negative amount going through the shunt in the other direction leaving whatever is left as a positive amount going to the battery.

This latter is sometimes true, but only when energy is going from the bank to the loads, not during charging when only the leftover energy is going **into** the bank

 

[highdesertranger]

ok I asked nicely once, consider this the second warning. look at the above post CC, BM, SC with no explanation of what these abbreviations mean. somehow we must include it in the post if it's to much trouble to write charge controller(CC), battery monitor(BM), solar controller(SC) then maybe you shouldn't be posting. write it out once in each post with the abbreviations in parentheses then you can abbreviate it. if we don't start doing this I will start delete posts. highdesertranger

 

[B and C]

Wow.  I think I finally got it through my pea brain.  The last part of the above sentence tells it all.  The charge goes through the shunt as a positive amount to the battery and the part going to the load is a negative amount going through the shunt in the other direction leaving whatever is left as a positive amount going to the battery.

Thanks for the discussion.  I just needed someone to talk it out with I guess.

The sentence you quoted is before this sentence.  I didn't delete it to kinda show how I got to the conclusion.  The bold part is what is pertinent.

Thanks again

 

[John61CT]

HDR you mean keep writing it out every new post when it's already been defined earlier in the thread?

I don't think that's reasonable?

 

[highdesertranger]

but they were not defined early in the thread I went back and checked. this thread is loaded with abbreviations. try to remember there are many newbies here and they don't learn from gibberish which abbreviations are. is it that hard? are we that lazy? highdesertranger

 

[Weight]

I think that it Is Reasonable. (delete sentence) Some of these threads go on for pages with many side tracked discussions. It would be better if our abbreviations were defined often in the thread. Especially as definitions can vary.

 

[frater secessus]

John, you're say the base load has no effect on end amps?

The physical/electrical position of the shunt means it only senses current to/from the battery bank. And that is what endAmps is measuring. Elegant, no?

This is why John referred to a properly installed setup. If it's not installed according to the manufacturer's instructions then it's measuring The Wrong Thing.

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