Cheap vs $200+ solar controller advice for newbie, please.

tanksalot · February 2015

I recently purchased and installed a used Kyocera KC187g 24 volt panel for my (smallish) RV. My brother's into solar, but he's also an EXTREME cheapskate. I turn to him for advice, but it's driving me nuts. When I got the panel, I also bought a cheapie $25 "MPPT controller" which appears to be working fine. I also bought a Tracer 1210RN solar controller on Amazon, but I'm concerned because the amperage rating is only 10 amps for a 12 volt system (my error).

I had read on the NAWS site that their Morningstar SunSaver 15 Amp MPPT Solar Charge Controller is what I should use. I'd naturally prefer to have a stable, dependable system, but am going nuts rationalizing paying $225 when my $25 cheapie SEEMS to work. I did also inherit some of that " cheapskatedness", but I can spend the money if I have to. I've invested $250 in new Trojan T-105's, and I do not want to jeapordise (?) them.

We're going to be moving our RV soon (we're in Quartzsite now) so I need to make a decision soon.

Thanks in advance for your opinions.

Tanksalot
Stan F.

BB. · February 2015

The Monringstar 15 amp 12/24 volt MPPT charge controller is a very nice little unit. The limitation is that, roughly its maximum solar array supported would be around 280 watt array (cost effective maximum) for a 12 volt battery bank...

If you ever plan on adding more panels to your RV, you might want to think about a larger charge controller (30 and 45 amp "nice"/not cheap units are available as the next size up).

If you do get the Morningstar, get the remote battery temperature sensor option. The little unit really needs that for accurate/optimum battery charging.

When looking at controllers, look at the prices for "options". LCD displays, remote battery temperatures sensors, remote computer interface, etc.... Some vendors include those in the base price, others as "not cheap" options.

-Bill

tanksalot · February 2015

BB:

Thanks for the reply. Please understand I'm NOT trying to contradict you (I'm not smart enough), but I still don't understand why I should pay almost 10X my cheapie from the used-panel guy for another controller, or why my Amazon unit isn't good enough (the amp rating is marginal, I know). I need the peace of mind, and have a digital voltage display hooked up to the cheapie controller which helps. I don't need bells and whistles, just a charged battery that doesn't get boiled or will run down. If the cheapie controller, or the Amazon unit will do the trick, I'll stop here.

Thanks again.
Stan F.

solar_dave · February 2015

If the SG stay good I would say you probably can stay on the cheapie. Did you actually measure the amps coming out of the controller when fully loaded? you are just below on the ragged edge of 5% if the 2 T105 are 225 amp, for a occasional use camping unit it may suffice.

BB. · February 2015

I never try to push anyone to buy hardware.. i try my best to answer the questions asked.

MPPT controllers tend to be more expensive because they have "costly" copper+ferrite inductors/toroid coils. A $25 unit--Many times they silkscreen MPPT on the cover and have just a PWM unit inside.

If the $25 unit meets your needs and is reliable.. Why not.

Some examples:

shift wrote: »

Re: Tri star charge controllers...

In the mean time if anyone happens to be pro with electronics and can provide some input based on the circuits let me know!

The third one is labled MPPT charge controller (first picture). But does not have enough copper to really do much:

Here is the Rouge 30 amp MPPT charge controller:

http://www.roguepowertech.com/products/chargecontrollers/mppt/mpt3048.htm (click on the more photos link if you wish)

Attachment not found.

That is type type of coil/toroid that one would expect to see (or even several).

-Bill

Photowhit · February 2015

If you're curious about the current it's putting out, stop by an auto shop that specializes in electronics, don't charge the battery that day and use it a bit. arrive at the shop near solar noon and hook up the charge controller and ask them if they will put a clamp meter on the cable and see how much current is flowing into the battery. If it's near or above the panels current rating it might be an MPPT type, if it's 50-75% it's likely an PWM type. Nothing wrong with this type of controller, you will just lose a large part of the wattage as it can only pass the current through and not reduce the voltage and recover some/most of it as current.

scrubjaysnest · March 2015

Photowhit wrote: »

If you're curious about the current it's putting out, stop by an auto shop that specializes in electronics, don't charge the battery that day and use it a bit. arrive at the shop near solar noon and hook up the charge controller and ask them if they will put a clamp meter on the cable and see how much current is flowing into the battery. If it's near or above the panels current rating it might be an MPPT type, if it's 50-75% it's likely an PWM type. Nothing wrong with this type of controller, you will just lose a large part of the wattage as it can only pass the current through and not reduce the voltage and recover some/most of it as current.

I'm not understanding your test method. With a PWM in summer full summer sun under your above conditions I measure 10.5 amps into and out of the PWM CC. That is an amp and half above rated for the panels. In winter sun conditions in AZ I measured 9 amps into and out of the PWM CC which is rated for my two panels. The summer test was with a Morningstar Sunsaver 10 and the winter test was a Morningstar TS-45. I seem to be missing something here. Maybe it is in the wattage available, 9amps @14.9 volts is about 134 watts for absorb in winter vs 156 watts in summer. Panel total rating is 160 watts

Maybe the answer is the mppt is a DC to DC converter and isolates the batteries from the panels where as the PWM since my measurements show during boost I get rated current but panel voltage is about 13 volts instead of the 17 one would expect. Hmmm, may have answered my own question

Photowhit · March 2015

Sorry for not getting back to you sooner, I'm beginning to loath our new forum software, which showed me as the last contributor to the thread!!!

How are you measuring the output? If you're not using a clamp meter and removing loads and testing at the wires, you're measuring the short circuit value rather than the actual output. Most auto electric repair shops should have a DC clamp meter, though perhaps you have one? The reason for the depleted battery is so the full current is utilized, as the battery becomes full the current it accepts is reduced.

scrubjaysnest · March 2015

Photowhit wrote: »

Sorry for not getting back to you sooner, I'm beginning to loath our new forum software, which showed me as the last contributor to the thread!!!

How are you measuring the output? If you're not using a clamp meter and removing loads and testing at the wires, you're measuring the short circuit value rather than the actual output. Most auto electric repair shops should have a DC clamp meter, though perhaps you have one? The reason for the depleted battery is so the full current is utilized, as the battery becomes full the current it accepts is reduced.

What I use is a Sears Clamp on current meter and a Fluke DVM, no loads on the system but what I failed to check was the input voltage to the CC from the panels under winter conditions. During boost in summer conditions the input to the CC would be 13 volts plus or minus a little. It would gradually increase until approx 80% soc when the CC would change to absorb mod. CC input would then be some where in the 17 volt range. Amps would taper off as expected during absorb. Its the 13 volts into the PWM CC during boost that makes me think the batteries are trying to draw so much current from the panels that panel internal resistance causes the voltage to be lower. With the mppt and the way the panels would appear to be isolated with the dc to dc conversion makes me believe mppt would work best during the boost charging phase where you want all the current possible with as high a voltage(within reason) possible. The OP's original question about cost is the real question. The TS-45 PWM is about $170 vs $400 plus for a TS-45 mppt. With small RV systems(under 400 watts) will MPPT give enough increase? In my case I would just add another panel.
In the OP's case I think the sunsaver 15 mppt might have value, but then I'm a Morningstar fan. While traveling we keep the wife's car on a 35 watt panel and a Sunsaver 10 PWM. Six or seven months later the car starts right up.

Photowhit · March 2015

Do you understand that when the batteries are charging in MPPT (I'll assume boost mode) the charge controller is creating extra current from the voltage above the needed point to charge the batteries. Once it reaches absorb the batteries accept less current. I'm not sure why the voltage would 'run away' at this point and I wouldn't like to see this, assuming this is measured with a load.

scrubjaysnest · March 2015

The higher voltage with the mppt is understood. What I'm not sure of is why; I believe this to be because the mppt with it's DC to DC conversion isolates the panel from the battery. I should also note that during boost while a battery wants all the current it can get, the makers have a recommended limit of typically 10x I/20. For my Exides that is about 50 amps per battery. All that aside the real question is the cost/benefit of a quality mppt vs pwm for small systems. The typical RV is under 400 watts and just about every system we saw out west this winter was 200 watts or less. We did see a lot that were also running a gen set in addition to the solar. It appeared the generator was for the drip coffee maker in the morning and the microwave at supper time.

Cheap vs $200+ solar controller advice for newbie, please.

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