killerniceguy wrote: ↑
Feb 18, 2018 11:17 am
Cleary I will have to step down the voltage to 12V. Something like this:
http://www.current-logic.com/shop/index ... cts_id=259
will step it down to 12V and also meet my amperage requirements of roughly 5amps at startup. The cooler typically pulls >1Ah during operation.
After doing some reading my concern is the power coming from the converter will be modified sine wave and not very good for the compressor in the cooler. Is there a way around this? Is there way to make it a pure sine wave?
I don't think I understand the problem, or maybe which equipment you're going to use.
IN general, if you have a 12v unit, it's almost certainly DC, not AC powered, and so you can't use anything with an AC (sinewave or otherwise) output at all.
Things with an AC output generaly are outputting 120VAC or thereabouts, which would also be about 10 times the voltage your device can handle on it's input. and would probably destroy it.
If instead you're going to convert the ebike battery power to 120VAC first, then power the device from it's own 120VAC-to-12VDC "wallwart" power supply, then keep in mind you'll be having a doulbe efficiency hit. So if it's say 75% efficient to convert your ebike power to AC, and 75% to convert that AC to 12VDC, then it's 75% x 75% = only 56% efficient overall.
As for whetehr the device's wallwart runs on modified sinewave, you'd have to check with the manufacturer; some do and some don't.
If I read the cooler page correctly, it says it runs on 12vdc, or 24vdc, or 120VAC. So you can use a step-down DC-DC with an input range at least as wide as your ebike batteries full-to-empty voltage, (each one has a different range) and an output voltage of either 12vDC or 24VDC.
Theoretically, the 24VDC should require less current, and be more efficient (less of a conversion down from the biek batteries), but that depends on how they designed the cooler.
Similarly, you can use a 120VAC output converter (again with an input range at least as wide as your ebike batteries' voltage range), but you'll probably want to check with the manufacturer about the sine vs modified sine issue, as well as startup currents and type of load (some converters don't handle inductive loads well).
And again, it depnds on teh cooler design if this is more or less efficient than running it on DC.
I figure I get about 10Ah from each pack, if I convert to 12v I should see about 40Ah per battery less the inefficiency of conversion right?
Depending on the converter and the specific load, you might get anywhere from 50% to 85% efficiency. You'd ahve to either test it when you get ot to see what it's efficiency is, or check with the manufacturer's spec sheets (if there are any).
THen multiply that effiency times the maximum capacity your packs can output *at the rate this load will use them at*.
The cooler has a low voltage cut off of about 10.7V, will this factor into available power reserves from the 18650 packs as the cutoff was put in place for Pb batteries?
Not directly--only in what your DC-DC converter has to be able to sustain output.
It *would* matter if you were going to directly power off the cells int eh packs, rebuilt into lower-voltage packs, but you're not doing that.