Charge controller power conversion efficency?

[kevinc_63366]

Just curious if anyone has an idea what the conversion efficiency is for MMPT charge controllers.

I'm particularly interested in MidNite's Classic line, but would appreciate any hard data points (or curves!).

Note I'm looking for power conversion efficiency, not parasitic power consumption type numbers.

e.g. If my panels are producing 1000 watts (10 amps at 100 volts) and that gets down regulated to 57.6 volts, what would the amperage be?

I'm not looking for an ohms law answer either <smile>. The answer will be something less than (1000/57.6) due to electronic inefficiencies. I'm just curious if they are on the order of 90% efficient? 95%? 98%?

Thanks.

[Sunking]

Varies by manufacture but MNS is 95 to 97% depending on what panel voltage you run with respect to battery voltage. The higher the voltage difference the lower the efficiency. However in any design you have to weigh cost of wiring with wire lengths. Many a time it is better to run at a higher voltage to save a lot of money and power losses on wiring between panel and controller. Target is 5% max with controller and wiring losses added together.

[kevinc_63366]

Perfect answer, exactly what I was looking for.

Thank you.

One followup:

Batteries do not charge at 100% effectiveness either, although the charge controllers do their best to maximize that.

Any good rule-of-thumb numbers for that stage of the process? e.g. If a charge controller pumps 80ah into a battery, how much actually sticks (vs. how much is wasted as heat). Presume a C/10 charge rate.

I have read that the slower the charge the more efficient it is, so long as the voltage pressure is maintained in the final stages (just shy of gassing levels). Acknowledging the stratification issue of a <C/12 charge rate, any other thoughts on that?

[Sunking]

FLA charging efficiency is average 80%. AGM up to 98%, Some lithium above 99%.

However it is accounted for in the initial design up front by multiplying your daily wh usage by 1.5 to account for all system losses. A FLA battery system at very best using MPPT is 67%, and PWM 50% efficient end to end. Grid Tied up to 80% In the final design stage you tweak the efficiency and design once all equipment and layouts are done. But when all is said and done the initial is very close and not much to be gained in the finale numbers.

[kevinc_63366]

Thanks again, great answer.

[PNjunction]

I have read that the slower the charge the more efficient it is, so long as the voltage pressure is maintained in the final stages (just shy of gassing levels). Acknowledging the stratification issue of a <C/12 charge rate, any other thoughts on that?

Along with stratification, very low levels of charge current take too long to charge the battery, and sulfate. Even though you may be able to get a full charge doing so, you will be walking down the capacity every cycle. This is why little battery tender / minder manufacturers warn people NOT to use it to recharge a decently discharged battery, but to use them as they were intended - tending to batteries that are already charged, OR yes, charging dinky little ones.

Perhaps this is what you are really after - a battery tender for an 800ah battery system, since you don't intend to do anything but sip a little power here and there from it, and hit it with a genny once in awhile. You don't care about stratification nor sulfation. So just hit it up with an 80ah charger, or solar system and be done with it, and let us know how it turns out.

[kevinc_63366]

You are right, I am trying to explore slower charge rates so that I can potentially use the generator less often. Just trying to get educated here with the WHY NOT information like you provided vs. simply being told "NO - Just do as I say."

Thank you for taking the time to explain.

Kevin

ps. "less generator" = "larger panel array". Panel arrays are the relatively cheap portion of the system, so just understanding the implications of doing something like a +20% array size vs. bank size vs. charge rate. Thanks again.

[Sunking]

You are right, I am trying to explore slower charge rates so that I can potentially use the generator less often.

Kevin that is a Oxymoron. The slower you charge the batteries, the more often you must use the generator. If the goal is less frequent generator use, then use higher charge rates by using higher panel wattage up to C/8. Go below C/12 and you will be using the generator frequently to EQ the batteries. There is a trade-off for everything.