Cheap China Solar Controller Failure

[RJsfishin]

For a couple days been noticing higher than the 14.6 voltage,.....going to 15, and even 15.5,....I knew something was not right. The next day it was showing 16, then quickly went to 17+.......I quickly loosened one battery wire !

As I posted before, @ 8 bucks each for the CMP-12 20 amp controller, I bought a spare, and now quite glad I did. I swapped them out, and all is well again.
So no more bragging about my cheap controller,..... which really did work very well for a year or so. Sometimes I just havta learn the hard way (:
Now I'm into the "not trusting" the swap out, so will be looking for something that is more reputable ??

Failed

[full_mosey]

BFL13 wrote:

full_mosey wrote:

NinerBikes wrote:

....
MPPT price points can make them prohibitively expensive in smaller systems.

Until you run out of roof real estate where adding panels is not possible. I'm there!

HTH;
John

You can tilt and get more that way 🙂 Or make a contraption! You need a project anyway, so why not?

I understand the value of tilting, it is just not convenient.

170W are on the roof of the van, my TV. I use the van for daily driving.

130W are on the roof of my TT. The roof does not support walking to get access to the part of the panel that needs raising. I couldn't even mount the panel to the roof, but had to run rails accross the roof from side to side.

HTH;
John

[Salvo]

OK, it seems I was way off on the WH efficiency. Trimetric says 70 to 80%, not my guesstimate of 90%.

Trimetric gives a conservative 94% for AH efficiency. They do say it can be as high as 98% during absorption. Though I didn't state it, the 100% I was referring to is during absorption.

There you have it. No one should be referring to WH when discussing battery charging. It may make their mppt system look good, but meaningless to battery charging.

[BFL13]

Salvo wrote:
Sure, once it gasses at 16V, it's probably zero percent. However in absorption, AH will be close to 100%, while WH is much lower. The surface charge voltage, battery and cable resistance all eat up watts, resulting in WH errors.

Barre says "gassing voltage" starts around 14.2v. Your curves on voltage where it take a jump are related to that AFAIK.

There are AH errors too, so I don't agree (at this stage anyway.) Check out the blurb in the Trimetic manual eg.

http://www.bogartengineering.com/sites/default/files/docs/TM-2025%20Users%20Instructions9-11-12.pdf

Page 10 of 16. Ref to "charge efficiency" factor P10. Also para 6.2 and 6.22 part 4

[Salvo]

Sure, once it gasses at 16V, it's probably zero percent. However in absorption, AH will be close to 100%, while WH is much lower. The surface charge voltage, battery and cable resistance all eat up watts, resulting in WH errors.

[BFL13]

Salvo wrote:
I believe you have it backwards. As far as I know, 100% of the AH gets stored in the battery, while perhaps 90% of WH goes in battery. The battery is fully charged at 12.8V, yet we're charging at 14.8V. Where are those 2 extra volts going? This is lost power that goes to heat. It's the cost of charging a battery. That's why WH is meaningless when you what to know how much you put into the battery.

BFL13 wrote:


Salvo, even if you use AH, you still don't know how many went into the battery and how much was lost to heat with "accuracy" AFAIK.

It is the same sort of thing in AH. Trimetric "allows" for ISTR 4% for heat on its AH counter over all the SOC range when recharging. They do say it goes crazy once the battery gets above 80% SOC. Barre, in his book, says it may be 10% on average.

If all you have is the AH figure for what the battery charger put out, you don't know how much went into the battery itself. Especially when that amount varies, where it gets really bad once the battery gets to "gassing voltage" and more of the total is lost to heat. Accuracy isn't even close. "It depends" etc.

[Salvo]

I believe you have it backwards. As far as I know, 100% of the AH gets stored in the battery, while perhaps 90% of WH goes in battery. The battery is fully charged at 12.8V, yet we're charging at 14.8V. Where are those 2 extra volts going? This is lost power that goes to heat. It's the cost of charging a battery. That's why WH is meaningless when you what to know how much you put into the battery.

BFL13 wrote:


Salvo, even if you use AH, you still don't know how many went into the battery and how much was lost to heat with "accuracy" AFAIK.

[BFL13]

There must be some sub-tile thing I don't understand, but I thought watt hours and amp hours would come out the same after conversion. Some people here have used the watt hours of their batts instead of AH and it all works out for them somehow.

Salvo, even if you use AH, you still don't know how many went into the battery and how much was lost to heat with "accuracy" AFAIK.

I use my Trimetric AH counter as an indicator and cross-check that with my "morning voltage" which is "close" to resting voltage before solar wake-up and the furnace is not on at the time. It is all just to keep track "close enough" while camping.

The hydrometer is the real decider but even it is tricky, where you have "SG lag" on a recharge. All is down to interpretation and experience with your own set-up to know what is going on "near enough."

Cross-checking is important though, as with anything. Even the multi-meter goes off kilter and reads high when its battery starts to fail. It can take a while before it gets so bad you notice the readings are too high unless you are cross- checking somehow.

[Salvo]

The only problem with that is the battery is rated in AH, not WH. I consider AH the correct unit of measure. You don't know how many AH went into the battery when dealing with watts.

I too like my Turnigy AH meter. It's connected between charge controller and battery.

MrWizard wrote:
i won't debate it any more, but wattHrs is more accurate

[jrnymn7]

hmmm, I do like the data history feature. And yes, I can see it being more accurate, just like Ah counting is more accurate than Vbatt for determining soc during use. Not sure if panel wattage would come into play though, seeing as mppt turns on and off (at least according to my understanding)?

[MrWizard]

i won't debate it any more, but wattHrs is more accurate

the meter i use shows me everything, amps, ampHrs, watt hrs, even the Lowest voltage the batteries got to overnight, when the fridge kicked on and the inverter surged

ampHrs at 11.5v is not the same power at 12.6v
wattHrs is absolute A*v, 120whrs ..1amp 120v for 1hr or 10a at 12v for 1 hr, or 1 amp at 12v for 10hrs
its all 120wHrs,
many people use ampHrs and many use 12.0v constant, but panels are rated in watts and different voltage and amps, and voltages much higher than use for 12v charging

when comparing many different items across a "system"
wattHrs eliminates much of the conversion needed , if everything is stated in wattHrs

[jrnymn7]

Mr.Wizard,

So what it really comes down to, is what sort of meter(s) you use? Be it Ah or Wh, it's just a different way of keeping track? Similar to using a voltmeter as opposed to an AH counter for determining soc?

[JiminDenver]

Fubeca wrote:
I have a $600 controller (of course I bought it used for $200). Maybe Jim and I can get together in the summer and do some side-by-side testing. I believe we have a couple of the same panels.

Well we had better do it soon. One of the 245w systems already sold, the other is spoken for.

Then again.....

What was your peak amps for the pair this last year. With the Eco-w's mine was 34.2a.

[MrWizard]

watt hrs is power used

if you know the items plugged into the iverter used 300Whrs and the lights 23whrs
you can just add it up, you don't have to converte back and forth to amps and ampHrs amphrs*v =wattHrs and the voltage is a sliding scale on DC
a kil-a-watt meter plugged into you inverter
or better yet a Turnigy watt/power meter in the DC power line
and one in the charge line
will tell you exactly how many amp hrs and how many wat thrs

the top line of the display is "at that moment" constant monitor
second line "right" shows the current Watts (8.22a*14.78v
the second line "left" rotates thru the accumulated data, will show amp hrs, watt hrs, peak amps, peak watts

several of us have them,very handy and cost about $30 rated for 65amps
i have mine between my solar controller output and the battery bank
i get daily readings of the exact amount of solar power returned to my system
where you mount them in the circuits determines what you will read

mine measures solar power returned to the system, but not what the converter adds to the batteries, and not the exact charge into the batteries

i used to have one mounted on the inverter power input wiring
for about a year i measured daily use in amphrs and watt hrs

comparing solar watthrs and inverter watt hrs, always gave a more accurate idea of power use and charge

jrnymn7 wrote:
Mr. Wizard, I appreciate what you're saying, but I still fail to see any real advantage to thinking in terms of WattHrs?

"2.8 amps @120v is 28amps at 12v, but at 12v its recharge time
so really you are likely using 24a at 12.x volts"

... which could essentially help compensate for some of the heat losses during charging, and thus help average out overall (i.e; actual) Ah usage/replacement.

I generally run between 12.5 and 12.8 volts, so the variance in amps used in any particular situation would be rather insignificant, I would think. So, I used an average of 2.79a, as opposed to 2.81a, for 10 minutes. No big deal. It's all about averages. Likewise, if half the time the fridge is using say 42w, and the other half its using 38w, it all averages out to 40w x 24hrs for 960wh's per day.

So, how does one then figure out how to replace 960wh's ?

[JiminDenver]

I knew my ears were burning at work today.

I'll go one better. I'll send them back after testing, most of them anyways. 😉

Personally I'm not upgrading for improved output, I'm doing it for the features. I'd get more power out of a extra panel/ Eco-W set up than I'd ever get spending a extra $300 on a fancy controller. Also I will be keeping the 230w/ Eco-w set up s a portable even after I mount the new panels. Come to think of it, if I could find more Schott poly's, I'd buy those.