Hi.. I recently got a new solar panel from somewhere... fell off truck... lolI know mppt is the way to go im mysituation but am asking for advice...panel 250 wattsvolts 30v.What would you do with this residential panel?\Someone told me the panel can produce up to 20 amps//Please guide me as I need help in this area. I can take pics if needed...Batterys are two 24 group 75 ah .

For a high voltage panel like that you basically have to use an MPPT controller. Yes, in great conditions you might see 20 amps out of the controller (not the panel) because 250 watt/ 12 volts = 20.8 amps. This would take very ideal conditions but it can happen.You can actually use this panel, or any panel for that matter, with a PWM controller, you'll just never get more than the Imp out of it which is probably about 8 or 9 amps. You'd be wasting half your potential power.

Hi,Because it is a high voltage panel an MPPT controller would extract more power than a PWM one.250/30 = 8.33 ampsSo if you use a PWM controller the solar harvest would be about 8.33 amps. There may be a risk that the PWM would not appreciate having 30 amps thrown at it, and it might let out the "magic blue smoke".On the other hand, with an MPPT controller harvest would be about 17 amps. The panel is a good fit for an ecoworthy 20 amp MPPT charge controller. They cost about $102.00

PWM would be a bad idea with this type of panel - you'll lose half the power. So the question is not "PWM or MPPT" but "which MPPT". Ecoworthy 20, while being pretty basic, is a good fit indeed. I wouldn't want it with my batteries - he is "too fast", so to speak ;) but then, I wouldn't want a solar smaller than 400W either.

I use a Morningstar MPPT-15 w/235 W panel. You would be giving up 5 A in ideal conditions if using the same. The Ecoworthy 20 A was talked about nicely in another recent solar thread on this Forum. The Morningstar has a lot of functionality and has battery temp compensation available.

Solar help... Mppt or PWM | Good Sam Community

Almot
Explorer III
Apr 29, 2016
lawrosa wrote:

Per the trojon site

Correct the charging voltage to compensate for temperatures above and below 80° F (26.6°C).

This is going to be a very long topic.
You don't believe anything, do you?

80F must be typo. Original formula is in Celsius.

Troja T105 data sheet:

"0.005 volt per cell for every 1°C below 25°C
0.0028 volt per cell for every 1°F below 77°F"

Once again, Absorb time should not be too long. In my controller it is both current-based and timer-based. Timer over-rides the current. I set the current to 0.7A and timer to 90 minutes. If it doesn't drop to 0.7A after 90 minutes, the timer will switch it to Float anyway. You don't want to boil your battery all day long.
Almot
Explorer III
Apr 29, 2016
red31 wrote:
pianotuna wrote:
From the Blue Sky 3024iD manual.

"The default compensation factor of –5.00mV/°C/cell is
appropriate for most lead-acid batteries."

but ya don't count every cell in all the strings of batteries.

I think Don didn't notice the number of zeros 0.028/10F vs 0.005/C. I almost made same mistake when reading those 0.028. Who measures these things in 10F anyway?
red31
Explorer
Apr 29, 2016
pianotuna wrote:
From the Blue Sky 3024iD manual.

"The default compensation factor of –5.00mV/°C/cell is
appropriate for most lead-acid batteries."

but ya don't count every cell in all the strings of batteries.

12v = 6 cell in the above formula. 1, 2, 4 batteries configured as 12v = 6 cell
lawrosa
Explorer
Apr 29, 2016
Almot wrote:
Lawrosa,

Some confusion here again.

Correct formula:
0.005 V per 1C per 2 V cell above or below 25C.

An equivalent variation if you can't use C:
0.028 V per 10F per 2 V cell above or below 77F.

Note that it's 77F, not 80F.

"Normally", temperature compensation is controller's job, not yours :)... Set and forget. Not the case with this controller, unfortunately.

Can or do I charge at the higher voltage until the amps taper to what? 3 amps? 1 amp?

I set my controller to switch to Float when current drops to 0.7A. You can't "set" yours, but try switching manually to Float when it drops to 1.5A maybe. There is no hard rule for that. If you always have some loads running, it may never drop below 2A.

Per the trojon site

Correct the charging voltage to compensate for temperatures above and below 80° F (26.6°C). (Add .028 volt per cell for every 10° below 80° F (26.6°C) and subtract 0.028 volt per cell for every 10° F (12.2°C) above 80° F (26.6° C))
Almot
Explorer III
Apr 29, 2016
Lawrosa,

Some confusion here again.

Correct formula:
0.005 V per 1C per 2 V cell above or below 25C.

An equivalent variation if you can't use C:
0.028 V per 10F per 2 V cell above or below 77F.

Note that it's 77F, not 80F.

"Normally", temperature compensation is controller's job, not yours :)... Set and forget. Not the case with this controller, unfortunately.

Can or do I charge at the higher voltage until the amps taper to what? 3 amps? 1 amp?

I set my controller to switch to Float when current drops to 0.7A. You can't "set" yours, but try switching manually to Float when it drops to 1.5A maybe. There is no hard rule for that. If you always have some loads running, it may never drop below 2A.
samhain7
Explorer
Apr 29, 2016
lawrosa
Again. Great post. I can see this thread being referenced frequently.
One other cool thing do you have a schematic of YOUR setup? Even a crude one.
Also some more detailed pictures? (One of everything hooked to your battery is something I don't think I have seen.
I am pretty much going to be an exact set up as you except I will be getting the Tracer controller.
pianotuna
Nomad III
Apr 29, 2016
From the Blue Sky 3024iD manual.

"The default compensation factor of –5.00mV/°C/cell is
appropriate for most lead-acid batteries."
pianotuna
Nomad III
Apr 29, 2016
"Battery charging voltage also changes with temperature. It will vary from about 2.74 volts per cell (16.4 volts) at -40 C to 2.3 volts per cell (13.8 volts) at 50 C. This is why you should have temperature compensation on your charger or charge control if your batteries are outside and/or subject to wide temperature variations. Some charge controls have temperature compensation built in (such as Morningstar) - this works fine if the controller is subject to the same temperatures as the batteries"
pianotuna
Nomad III
Apr 29, 2016
Hi,

That is not what I have read.

lawrosa wrote:
pianotuna wrote:
Hi,

I believe this is a misunderstanding. The charge voltage needs to increase by a particular amount for every degree below 77 F (25 c).

It needs to be decrease by that same number for every degree above 77 f (25 c).

lawrosa wrote:

Yes I know to raise or lower the volts .028 per cell for every 10 degrees above or below 80f. This equates to .336 volts for 12 cells.

Its every 10 degrees in ambient temperature not 1 degree..At least thats what I read from all the battery manufactures sites pretty much..
lawrosa
Explorer
Apr 29, 2016
pianotuna wrote:
Hi,

I believe this is a misunderstanding. The charge voltage needs to increase by a particular amount for every degree below 77 F (25 c).

It needs to be decrease by that same number for every degree above 77 f (25 c).

lawrosa wrote:

Yes I know to raise or lower the volts .028 per cell for every 10 degrees above or below 80f. This equates to .336 volts for 12 cells.

Its every 10 degrees in ambient temperature not 1 degree..At least thats what I read from all the battery manufactures sites pretty much..

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