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12 volt to 24 volt conversion Notes

chrisski

Solar Boondocker
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Aug 14, 2020
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I am in the process of upgrading from 12 volts to 24 volts, and my first step I finished yesterday about installing a 24 volt inverter and rearranging the four golf cart batteries to 4 S. I measured the am draw on my 12 volt appliances, and I was expecting some 24 volt to 12 volt conversion losses, but these are the amperage draws on some items in my RV on the old 12 votl system versus the new 24 volt system:

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There were only a couple of items that tested about the same between the 12 volt and 24 volt at a 1 to 2 ratio like I expected. Most were a bit less efficient at this higher voltage. Just wondering if anyone kept track of this.
 
I don’t remember the explanation for why this happens but the RV furnace and bathroom fan don’t surprise me based on past observations.
 
I'm scratching my head on this. Was the expectation that (across the board) you would see half the amp draw on 24 volt than you saw when on 12 volt?
 
Yes. Half the amps is what I expected, which with my math comes out to 100% efficient.

Really wondering have others measured this?

- Perhaps the coffee pot needed more watts because the water was colder.

- Maybe the RV idle draw went up because more devices came out of sleep mode or could have been the idle draw of the converter.

-Orher devices are difficult to measure because they fluctuate, so I just have to go with a number. The water pump was one which went from 5 to 6.5 but was usually at 5, so hard to put a number on it.
 
From the 50,000' view, would it be safe to say that your 12 volt devices are drawing more current than can be explained by the converter's efficiency? What's the overall loss of efficiency?

It looks like the more current a device draws, the more efficient the converter is.
 
From the 50,000' view, would it be safe to say that your 12 volt devices are drawing more current than can be explained by the converter's efficiency? What's the overall loss of efficiency?

It looks like the more current a device draws, the more efficient the converter is.
When I go out this next time I’ll check that. That would match what is suppose to happen with an inverter.

Probably would use the clamp meter at the converter versus the battery shunt. That should take away the “noise” the inverter may make and the other 24vdc devices. I will be removing this converter to install a fuse. I might come up with some constant load devices to hook up and try with the power supply.
 
In prep for putting the lithiums in, I’m changing from a 200 amp ANL to a 225 class T. Quite a difference in size! Reading the dimensions is one thing, seeing it is another.
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Size matters!
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Is your buck converter outputting 12v or 13.8v? If higher than 12v, that might explain the lower than expected currents.
 
I do have it set to 13.2 volts. That could be part of it. I don’t know what the battery voltage was when I did the test.
 
And what was the 24v battery voltage? I wonder if you could compare the actual wattage used instead of amperage?
 
This is the after picture of getting the 225 amp class t fuse.

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Involved making a bus bar and tinning it.
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Ended the day with the Main battery fuse above and an Two ANL fuses for the DC to DC converter.F7C1DE90-534D-43DD-95B2-1DABE06617F9.jpeg7293742D-B2AC-42FB-8A6D-29D3E5598E4B.jpeg
 
I'm getting ready to put in a new common positive bus bar and with it, make better connections between it and the same switch you have and the the same Class T fuse holder. I'm currently using 2/0 cable between the devices but I'm going to check to see how closely the levels of the three devices are in hopes I can use bus bars to make the connections instead.

All three devices are Blue Sea, but I suspect they all have different connection elevations. It would be nice if Blue Sea was consistent, but the dimensioned drawings on their website are inconclusive.
 
All three devices are Blue Sea, but I suspect they all have different connection elevations. It would be nice if Blue Sea was consistent, but the dimensioned drawings on their website are inconclusive.
That happened to me today. The class T fuse fit with the homemade busbar to the Blue sea switch with a piece of plastic underneath it, and the wire fromthe switch to the 8 stud 3/8” busbar had enough flexibility to fit. Considered using 1/4” washers under somethign for spacing. You get the picture.
 
That happened to me today. The class T fuse fit with the homemade busbar to the Blue sea switch with a piece of plastic underneath it, and the wire fromthe switch to the 8 stud 3/8” busbar had enough flexibility to fit. Considered using 1/4” washers under somethign for spacing. You get the picture.

I think spacers to get all the devices on the same plane is going to be a better plan than trying to bend the bus bars to match. But I may break out the BFH and try to bend the copper bar just to see if how well it works.
 
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