level 1 vs level 2 losses?

[BrockWI]

I am relatively new to this, but familiar with charging larger battery banks. We have a 24kw SLA battery bank running at 48v feeding a xantrex 6048 inverter with our solar PV setup.

Anyway for our first week used used the level 1 120v charger and looking at the kwh used and now using the level 2 charger I noticed a significant drop in KWH from the same apparent SOC.

So what I am wondering is what is the on-board charging / system loss? Lets just assume it's 100w to have it on and charging. If that's the case and you had to charge 18kwh the level 2 for three hours is 300w lost. The same thing on level 1 would be 16 hours and at 100w its a loss of 1600w. That seems to me to be quite significant and something I hadn't thought of when using a level 1 charger for the long run.

Thoughts?

 

[DaveEV]

Yes, charging on 120V / L1 is less efficient than charging on 240V / L2.

IIRC 240V is around 85-87% efficient, while 120V is around 75% efficient and as you've guessed, the difference is from the overhead in powering the car, cooling pumps, etc, while charging.

 

[smkettner]

I thought the systems overhead was closer to 300w. The longer you charge the longer you are wasting that 300w.

 

[BrockWI]

I have no idea what the "standard" loss is (but am curious), but I would imagine charging a 300+volt pack with 120v vs charging 300+ volt pack with 240, 240 would require less step up to get you there, thus less loss there as well. The things you think about or don't

 

[Stanton]

I thought the systems overhead was closer to 300w. The longer you charge the longer you are wasting that 300w.

Correct!

 

[johnrhansen]

I was thinking... Just what is happening when you charge the car... the battery is about 400 volts right? so when you charge at 240, I imagine you could get about that DC when you figure for conversion and inefficiency and the like... So you have to bump the voltage up with something. Most likely there is a transformer in there somewhere... If you are charging at 120 volts instead, you have to run the current through the same number of transformers.. (to raise a lower voltage to the battery voltage) just half in series with the other half. So you have the same transformer losses with a quarter of the power. Maybe that's where some of the extra losses come from? I was charging my car level 1 yesterday, and I heard no fans running.

 

[GRA]

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