Cheap China Solar Controller Failure

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

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.

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

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.

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.

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.

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.

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

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)?

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