UPS as a portable power supply.

rebelrider.mike

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May 25, 2017
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382
I found out a while back, that if you measure Voltage across an inverter that is not pure sine wave, you get an incorrect reading. It has to do with the RMS value of AC Voltage. For example, a pure sine Voltage of 12V would be more like 17V at the peak, but the mean value is 12V. I may be oversimplifying it, but I still don't understand it very well.

The point is, for an impure sine wave inverter to be measured properly, you need a "true RMS" Voltmeter. I finally got one the other day and used it to measure my little power box.

image_jrpvoe.jpg


You can see the "True RMS" Voltage is 117.5V vs the standard multimeter reading 96.3V. Just for fun, I measured the frequency too:

image_ffiupn.jpg


I don't know if the 58.65Hz is a nice wave, or if it's all squiggly. I wish I had an oscilloscope. Oh well, I'm having fun with the new things on this meter though. :)

I've had the box on a few camping trips since I built it. Haven't had any heat issues, but I've been using the 12V plug and USB ports mostly, since most things camping are DC anyway. I do want to add a fuse to the battery though. And I still need to re-label the top.
 

Korishan

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Jan 7, 2017
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I've built, and redesigning, an AC meter that is based off of the Open Energy Monitor. I can read IRMS, VRMS, and many other things. Can give an accurate wattage usage (within the realms of the arduino, currently) and can even see what the peak loads are.

Pretty neat setup. I will be expanding on my current setup as I want to use at least a 14-bit ADC instead of the 10-bit in the arduino. 1024 steps isn't high enough resolution
 

rebelrider.mike

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May 25, 2017
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382
I have a trip coming up and wanted to expand the capacity of my little power box. The situation will be that there is no power, and the people I'm with will want to be charging phones, cameras, portable chargers and stuff. The internal battery is a 3s5p, and has 8.7Ah in each series.

Let's see if I can do the math right: 8.7Ah x 3s x 3.7V = 96.57Wh, I think.
The extension battery will be 3s12p with 18.2Ah per series. 18.2Ah x 3s x 3.7V = 202Wh
So in parallel, they should have about 298Wh. Even with losses, I'm hoping that will charge a lot of cell phones! More than 96Wh at least. Cell phones are something like 5 or 6Wh now-a-days right?

Anyway, I was looking around for something to house the new cells in since they won't fit in the power box. I've got a lot of these stacked up:

image_wbzgli.jpg


I made each one to hold a parallel group of 12 cells.

image_ptieue.jpg


Made terminals out of nuts and bolts, and connected them together. They're charging up nicely.

image_tplazx.jpg


They're not completely finished yet. I want a fuse in line, maybe 7.5A,and I need to secure them to a board or something. They're pretty unwieldy and not portable right now. I'd also like to put some kind of protective foam layer on the top and bottom of the cells so they don't move around inside the containers.

I wonder if I should adapt a balance cable to go between the two batteries also?
 

Riplash

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May 27, 2018
Messages
66
Korishan said:
I've built, and redesigning, an AC meter that is based off of the Open Energy Monitor. I can read IRMS, VRMS, and many other things. Can give an accurate wattage usage (within the realms of the arduino, currently) and can even see what the peak loads are.

Pretty neat setup. I will be expanding on my current setup as I want to use at least a 14-bit ADC instead of the 10-bit in the arduino. 1024 steps isn't high enough resolution

I don't want to highjack this thread too much, but Korishan what are yourthoughts about making an Arduino based cheaposcilliscope? I have seen some online plans for some, but have more important projects in front of that project. I bet it would be cool for rebelrider mike to hook it up to a true sine wave inverter and compare it to a modified sine wave inverter, as well as a lot of other powerwall stuff?

-Ryan
 

rebelrider.mike

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May 25, 2017
Messages
382
Revisiting this modified UPS power box.

I've had it on a few trips, and it works great. But I've decided to add a few improvements and safety features.

image_xwsvke.jpg


The main thing is I wanted to install a BMS for the 3s battery. Mainly to keep it for undervolting. Also, everything was soldered directly to the battery, so in order to remove it, I have to get the solder iron out. So I've added connectors that will let me completely separate the battery from the circuit board and also the wiring and such that stays in the box when the board is removed. This makes for much easier tinkering! Also, the battery got more foam padding, just to protect it from the occasional bump when traveling.

image_rhbobg.jpg


The BMS works great with the 5V and 12V parts, but when I turn on the inverter, the BMS suddenly shuts off. I wonder if there is a sudden power draw that the BMS is interpreting as a short or over current? Perhaps a capacitor would help? If I can't solve that issue, I'll at least put a main fuse in somewhere.

I think I want one anyway on the 12V part as the board allows way more current than the battery can safely deliver. That's not a problem for the 5V, as it is only used for charging USB devices. Even at full capacity on the boost boards, the maximum draw would be 30W. Which is also the maximum for the battery.

The thing about the inverter though, is that I've not used it except to test it. I never seem to come across any situations where an AC source of power would come in handy while camping. Because of this, I've moved the Voltmeter wiring so that it turns on with the USB ports instead of the big inverter switch.

One cosmetic thing I did was to sand off the obsolete labels on the top and add in my own with a kind of silver paint pen. Except for one smudge, I think it looks pretty sharp.

image_szlvok.jpg


I did accidentally write 2A instead of 3A for the USB ports, but that's ok. Not really supposed to use things to their limit anyway. And I made a 12V socket adapter, since lots of things plug into 12V car sockets.

Future stuff I'd like to do is:
- figure out the BMS/inverter issue.
-add a 5A fuse to the 12V side.
-fix a broken screw thingy that keeps the back cover on.
-fill in the obsolete ground holes with JB Weld.
-upgrade the battery with higher capacity cells.
 
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