Charge controller and battery meter questions

Plowman · October 2014

Re: Charge controller and battery meter questions

Cariboocoot wrote: »

I don't see why you think the Kid is too small, as it will handle 30 Amps and that is more than enough for 225 Amps hours which apparently is what you've got.

I was thinking with my 4 panels.

Could I still use 4 panels during periods of poor insolation (winter mostly)? They all have individual breakers and can easily be turned on and off. I got 4 panels in large part to deal with winter conditions in the Northwest (overcast and drizzly).

Cariboocoot · October 2014

Re: Charge controller and battery meter questions

Plowman wrote: »

I was thinking with my 4 panels.

Could I still use 4 panels during periods of poor insolation (winter mostly)? They all have individual breakers and can easily be turned on and off. I got 4 panels in large part to deal with winter conditions in the Northwest.

Yes, you could do this. You just have to remember to turn panel #4 on/off as conditions require and that panel production tends to drop off drastically with poor insolation so even 30% more may not be enough. I doubt the Kid would be hurt by an additional 10 Amp potential, it's just a waste of panel (they tend to cap over-paneling at 20%).

inetdog · October 2014

Re: Charge controller and battery meter questions

Cariboocoot wrote: »

This is the problem with load allowance. The controller can not know how much is going to battery and how much is going to load unless there is a shunt to measure each. From what vtMaps says the Classic is reading its internal current and comparing it to the external measurement on the WhizBang Jr. to determine this. That makes sense.

FWIW, the CC does not actually need to know how much current it is putting out to do a proper Bulk Amps and End Amps based strategy, so one shunt is all it takes to implement that behavior.
But it does have to recognize when the current is below End Amps only because the input PV power is limited.
It is still nice to also know what is going to a load for display and logging purposes, and any CC that is able to roughly calculate its own output would not need an additional external shunt.

Plowman · October 2014

Re: Charge controller and battery meter questions

Cariboocoot wrote: »

Yes, you could do this. You just have to remember to turn panel #4 on/off as conditions require and that panel production tends to drop off drastically with poor insolation so even 30% more may not be enough. I doubt the Kid would be hurt by an additional 10 Amp potential, it's just a waste of panel (they tend to cap over-paneling at 20%).

Thanks. I'll have to ask Midnite if leaving all 4 panels on would damage the Kid.

How much do you think a Kid with my 4 panels would improve production during the winter? Say during typical Northwest winter conditions, overcast and ~40F outside. Imp of my panels is 8.47, Vmp is 18.9. Vancouver, BC, has very similar conditions to my corner of Oregon.

I did a quick calculation and came up with a ~20% increase, but I don't have a high confidence in my figures. Here are my guestimates, assuming panels are producing at full voltage (due to cold) but only 1 amp/each (due to poor insolation). No idea if those are valid assumptions.

1.0 amps per panel
18.9 voltage
18.9 watts per panel

18.0 voltage of MPPT controller (95% efficient)
14.8 voltage of PWM controller

71.8 Watts with 4 panels + MPPT
59.2 Watts with 4 panels + PWM

vtmaps · October 2014

Re: Charge controller and battery meter questions

Plowman wrote: »

Thanks. I'll have to ask Midnite if leaving all 4 panels on would damage the Kid.

That has been answered by the Midnite engineers on their forum. Over paneling will not damage the kid.

On the other hand, running any power electronics at its thermal limits will shorten its life... I guess that shortening its life is not the same as damaging it.

--vtMaps

Photowhit · October 2014

Re: Charge controller and battery meter questions

Plowman wrote: »

18.0 voltage of MPPT controller (95% efficient)
14.8 voltage of PWM controller

71.8 Watts with 4 panels + MPPT
59.2 Watts with 4 panels + PWM

Your math is fine, but you understand that it will be more and less than that?
When in bulk and your voltage is below absorb you will have greater advantage since the voltage will be lower, once you reach absorption, you will be at the level you've done the math for until the batteries reduce the amount of current they will absorb, if you were charging at 10% that would happen pretty quick, but at the reduced current you will be there for a while...

Cariboocoot · October 2014

Re: Charge controller and battery meter questions

Actually you will not see much advantage to running 4 panels on the Kid over 3 most of the time. This is because the 3 panels have the ability to max out a 30 Amp MPPT controller to begin with:

3 * 158 = 474 * 0.77 / 12 = 30 Amps
4 * 158 = 632 * 0.77 / 12 = 40 Amps

The Kid will only pass 30 Amps. The MPPT advantage gained in cold temps will not be fully realized because the derated output is already at maximum. The advantage of the extra panel on less-than-sunny days is unpredictable.

Plowman · October 2014

Re: Charge controller and battery meter questions

Cariboocoot wrote: »

Actually you will not see much advantage to running 4 panels on the Kid over 3 most of the time. This is because the 3 panels have the ability to max out a 30 Amp MPPT controller to begin with.

I was talking about cloudy days only, I understand 4 panels is too much for the Kid when they're producing at maximum. Just trying to see if it would be worth it to get a Kid to deal with winter conditions.

I don't have a good understanding of my panel voltage, not a metric I keep track of. I have observed low amp output during overcast days. Hence the assumptions in my little worksheet, 18.9V but only 1 amp output per panel.

I think I mentioned in my OP that I'm going to buy a shunt-based meter, sooner rather than later, which is what got me thinking about a Midnite Kid. I'd rather get a Whiz Bang than a Trimetric, but if the Kid won't help me increase winter output, then I'll probably just go with the Trimetric, which I can use with my existing system. As far as I can tell the Whiz Bang can only be used with Midnite controllers, correct?

gww1 · October 2014

Re: Charge controller and battery meter questions

I was talking about cloudy days only, I understand 4 panels is too much for the Kid when they're producing at maximum. Just trying to see if it would be worth it to get a Kid to deal with winter conditions.

I have 5600 watts pv aray. Yesterday and today it was raining and I got 2 kwh total production per day. The only time I could see 4 panels help is on the bright sunny hot days of summer. If the sun comes out in winter you will be at max with 3 panels. If the sun don't come out you could have 50 panels and not max out the cc.

Good luck
gww

Plowman · October 2014

Re: Charge controller and battery meter questions

Photowhit wrote: »

Your math is fine, but you understand that it will be more and less than that?

Yeah, my assumptions were somewhat arbitrary, I just wanted to crunch some numbers. It does appear that an MPPT controller would work better under the conditions I assumed, but I don't know if these assumptions are warranted. I haven't lived with my little solar electric system in winter yet.

Is high voltage + low amps a valid assumption for cold overcast conditions?

Photowhit · October 2014

Re: Charge controller and battery meter questions

Plowman wrote: »

Yeah, my assumptions were somewhat arbitrary, I just wanted to crunch some numbers. It does appear that an MPPT controller would work better under the conditions I assumed, but I don't know if these assumptions are warranted. I haven't lived with my little solar electric system in winter yet.

Is high voltage + low amps a valid assumption for cold overcast conditions?

I think with the panels you have, since they have a relatively high vmp of 18.9, you might do better than others think with the Kid. I just speculate that the through amperage on a PWM CC at 18.9 VMP is likely very close to 30, and on a MPPT 30 amp CC you will be near the same, I do think you will 'flatten your curve, having the 30 amps longer when you would be more marginal early and late in the day. This charge rate is fine for your current battery bank, and if you choose to expand in the future and go to a 24v system it will increase your options. I would leave the panels attached, I think you checked over on the Midnite forum and basically got an 'A okay' response for this.

I'd also keep your Morningstar CC, you may find that you will use it when/if you expand the system. I haven't read much over on the Midnite forum, but have suspected that the Whiz Bang will enable the 2 CC to work better together, if you choose to expand. Since it's measuring the total current going into the batteries it should be able to make choices based on this information to help regulate the cycles.

I was about to head over to the Midnite forum, since I presented the over paneled for the battery bank situation I have, and see what their thoughts were.

I do think it will help, somewhat, on your overcast days, but as others have pointed out 20% more than a little is a pretty small number.

gww1 · October 2014

Re: Charge controller and battery meter questions

I plan on over paneling someday cause it is the only way to add more to my cc's. I agree with what photowhit says. I just think on overcast days you get nothing and there is no way to improve on that. The rest of the time it will probly help more then hurt. For the cost, I don't know but once you got it it won't cost more to use it.
cheers
gww

Photowhit · October 2014

Re: Charge controller and battery meter questions

Not cost effective, only in the sense of wanting to add a battery monitoring system and were to spend you money wisely. The added effects will be minimal (didn't I hear 'Coot say that 4 pages ago) but I'd think it would be money more wisely spent than a trimetric, though 2x the cost.

You could just use what you have, it might be a bit nerve racking the first winter, but you have a genny. Then look at where you want to go and what you feel you need in the future. I think you talked about switching to an electric fridge?(I'm easily confused though...lol) If so, you might want to use this system until the battery bank is about to fail and go to a classic (which comes with a Whiz Bang Jr) and a 24v(or48v) system.

Plowman · October 2014

Re: Charge controller and battery meter questions

Thanks for the responses folks. If money was no object, I'd just get a Midnite Classic (and more panels and batteries), but I'm poor. The cash outlay is a big deal to me, especially having spent close to $2000 on my system this year, which is a good chunk of my annual income.

I might be able to justify up to $500 more, but it'd have to result in a significant improvement in the performance or management of the system. A Trimetric would qualify, as would a bigger, true sine inverter (I'm thinking Xantrex Prowatt 1000W). Doesn't look like the Kid would result in a significant improvement in the winter, not enough to justify the expense at least.

Photowhit · October 2014

Re: Charge controller and battery meter questions

Save your money, claim your tax credit, and your on your way. I did several of my expansions with the help of the tax credit and no electric bill... You might have some issues with none inspected equipment depending on your local, installation codes if any...

Cariboocoot · October 2014

Re: Charge controller and battery meter questions

The effect of cold and the effect of cloud are two different things.

The first is predictable, in that a panel has a temperature coefficient and so a reasonable estimate of increased/decreased Voltage for a given temperature can be calculated. There is not going to be much advantage here because the Vmp is already high enough to make up for reasonable V-drop under normal conditions and still max out the controller, so further Voltage increase under cold conditions will result in higher Voltage but the power gained from that can not be realized.

The second can't be predicted because there is no standard for "cloudy". Panels may produce 1/2 their current, 1/10 their current, or no current at all. Panels are a current source and will try to produce Imp 'first' as it were. If they can not produce current at Batt V then no charging takes place. Changing the Voltage up usually does not result in any improvement in charging because 2V is 0.5I.

In other words you could have 10X as much panel as you'd normally need and still have zero charging on a cloudy day, depending on how cloudy it is. It really won't matter much if it's configured as all parallel at 18 Volts or all serial at 180 Volts. Above a certain point it's just a waste of PV - and money.

Plowman · October 2014

Re: Charge controller and battery meter questions

I understood most of that Cariboocoot

I do understand that the answer to my question about how my system will perform in the winter is "it depends." I'll just have to see. I've only had the 4 panels up and running for 7 weeks now, had 2 panels for a few months before that. Have not lived with solar in the winter. Yet.

Should be an interesting learning experience. Can't be any worse than last winter, when I was totally reliant on my generator. I'll see how it does, and if performance is unacceptable, I'll consider getting a larger MPPT controller and possibly more panels and batteries next year.

Alaska Man · October 2014

Re: Charge controller and battery meter questions

I have found charging in the morning with my generator and letting the sun finish off the recharge is the most efficeint way to go. If like me you are only going to get 3-4 hours of usable sun a day during the depth of winter, you might want to give it a try.

I'm not sure about what you have for a charger, but I can bring my bank from 75%-80% up to 94%-95% in little over an hour. With my Yamaha that's about 4 cups of gas. You can buy a lot of cups of gas for the cost of a more panels and another MPPT controller.

I do think you will find more batteries would work better for you than more PVs.

Constantine Faller · September 2015

vtmaps said:

Re: Charge controller and battery meter questions

Bottom line: equalize, and then know for sure where you stand. If it turns out that your batteries are getting fully charged, then adjust your controller to spend less time in absorb. If they are not getting fully charged, we can troubleshoot... maybe it is the controller... but first you need to know for sure the SOC of your batteries.

SG is, of course, the gold standard for SOC. But you cannot read your hydrometer to a resolution high enough to differentiate between 99% SOC and 100% SOC. Consider this: If you are repeatedly charging up to 99.9% SOC, that 99.9% becomes your new 100%. After awhile, your battery is reduced to 99.9% of 99.9% of 99.9% etc. This is slow deficit charging and the SG slowly declines as more and more electrolyte is lost to sulfation.

If you do have sulfation and it has been longstanding, it is probably not reversible. 95% may be the new 100% for your batteries. Or maybe not. An EQ will bring your batteries to their fullest potential.. what ever that may be. If you reverse some sulfation (assuming there is sulfation and that it is reversible), you can expect to see a bit of an increase in your end amps.

--vtMaps

Hoping it is ok to post on an older thread -

I have a question on the above comments, and others, on 100% SOC:

Do we use the SOC after an equalization as the 100% SOC baseline, cuz it would seem it is actually an overcharge with SGs commonly 1.800, 1.900, or higher, and voltages to match?
or
Is our new, age adjusted baseline, whether we call it 99.999% or 100%, what can be achieved after the next full absorb charge with voltage of 2.4 - 2.45 v/cell?
or other

* roughly speaking, full being no rise in SG in 1 or 2 hours (hydrometer accuracy + 0.002)

Constantine Faller · September 2015

And thank you for pointing out that manufacturers can potentially lessen warranty claims by recommending higher charging voltages that might not necessarily maximize the service life of the battery.

vtmaps · September 2015

Constantine Faller said:

Do we use the SOC after an equalization as the 100% SOC baseline, cuz it would seem it is actually an overcharge with SGs commonly 1.800, 1.900, or higher, and voltages to match?

In THEORY, the highest SG you can achieve is 100% for that battery. There is certain amount of sulfur in a battery cell. It exists as sulfuric acid and/or lead sulfate. When all the sulfur is sulfuric acid, the battery is at 100% SOC and the SG can go no higher.

In PRACTICE, several folks have observed that the SG of an overcharged battery may slightly exceed the manufacturer's specified SG. The effect is transient, if you charge the battery and let it sit for awhile the SG will drop back to specification.

I don't know how to explain the effect (if, in fact it is real). Perhaps overcharging drives some other chemical into the electrolyte. Remember, an hydrometer does not measure sulfuric acid concentration... it measures SG. If we ASSUME that the electrolyte is only sulfuric acid and water, then we can infer the sulfuric acid concentration from the SG. If there is something else in the electrolyte, the SG may not be attributed solely to sulfuric acid.

Does that answer your question?

--vtMaps

inetdog · September 2015

Maybe I am just misreading the OP's information, but this is what I think I see:

OP: My CC is staying in Absorb too long and my batteries are NOT getting fully charged because of that.
I see this as a major logical error. The OP does not want to program a shorter Absorb, he wants to get to a higher SOC during the available Absorb time.

The solution is either to extend the Absorb (PV output willing) or increase the current during the Absorb stage.
Since many battery makers suggest a time of 6 or more hours at the Absorb voltage before switching to Float, that is just not possible with PV. The solution is to accept that the PV driven charging cycle is not compatible with the mains driven cycle recommended by the maker.

If you set a higher Absorb voltage the current will necessarily remain higher during the Absorb stage. As long as you do not exceed C/10 or get to 100% SOC before you run out of sun or switch to Float you will not be damaging your FLA batteries.

One potential monkey wrench you should keep your eye out for is that if for some reason you don't draw down the batteries at all one day, the next days charge cycle will start at a near 100% SOC. And the higher Absorb voltage may not let the CC switch to Float normally based on the End Amps setting. So you may want to set End Amps higher and also raise the Float voltage if you go down this route.

If you do not have a battery shunt and so cannot distinguish battery end amps from load current, you have a bigger problem and will have to experiment some more.
Your goal is to get as close as possible to 100% SOC each day, even if you have to increase the Absorb voltage to do it.

PS: The reason that the Bulk stage is ending too soon (if it is) is basically that the Absorb voltage is set too low.
The proper Absorb voltage should allow a smooth transition from full Bulk current to a gradually decreasing charge current that starts at that same value as the Bulk current.

PPS: You have probably done this already, but the battery voltage should be measured at the terminals. If the resistance of the wire and connectors from the CC to the battery bank is too high the CC will be reacting to an incorrect battery voltage.
Same with temperature compensation if provided. If the CC thinks that the battery temp is higher than it really is it may cut the voltage back too low. And at least some CCs with remote temp sensing conveniently display the nominal voltage while delivering the temperature compensated voltage.

Charge controller and battery meter questions

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