DIY Capacity tester

[Freep]

I don't have a capacity tester, I have 4 271 cells arriving Friday and I don't want to wait another month for a capacity tester to arrive. What I do have is a 400 watt inverter, a Kill a watt and a hair dryer. I also have a hot plate. I could buy a bigger inverter locally if I need to.

I can do a basic capacity test with that, right?

 

[Ampster]

I can do a basic capacity test with that, right?

You will need something to measure Amphours to be accurate. Just Amps over time has to be logged because volts and Amps may change over the process of discharge.

 

[gnubie]

Yes, you can do a rough capacity test.

Your inverter will have an efficiency rating, check the manual or ads for it. If you can believe that rating it will usually be at peak load so you would need to run your inverter near peak to get that ratings. At low loads inverters can have quite bad efficiency levels. I tested my own Giandel and it was around 60%. This is partly because there is a fixed component to the loss figure, the lighter the load the more significant that fixed loss is.

When you see the watt hour figure on the kill-a-watt you'll need to multiply that value by your inverter's efficiency figure to account for the loss there.

400 watts is pretty small, unless the hair dryer is on low it'll probably overload it, and even then perhaps still. The hot plate almost certainly will, but check their watt ratings, anything is possible.

 

[Freep]

According to the manual the KWH/Hour function displays the cumulative energy consumption since power was applied to the unit. So time should be covered.

Wow 60% efficiency? I'll keep that in mind. It's a Duracell DRINV400

I'm itching to get this bank in the camper and put it to use for geographic distancing for the next month. I just need a rough test. I will do more detailed testing when I get back and install the big inverter.

 

[gnubie]

If you can borrow a clamp meter you can work out the efficiency of your inverter at a given load since it doesn't seem to be mentioned in that PDF. DC volts x amps into the inverter gives watts in, then check the watts out with your kill-a-watt and you can divide to get the efficiency figure. You could monitor the amps x volts into the inverter this way too but you have to sit around and log values as Ampster said.

 

[Freep]

Great idea. I happen to have a clamp meter.