Kill A Watt meter readings

[featherliteCT1]

I bought this Kill A Watt meter and measured the amps and watts while I charged my 12v DC battery bank using an 120v AC powered battery charger.

The Kill A Watt meter read .85 amps and 250 watts.

My Trimetric TM 2030 meter simultaneously read values of 28 amps and 360 watts (approx). That makes sense to me because 360w/12v= 28 amps.

My Multi Meter also read 28 amps.

Does this make sense?

Kill A Watt Meter.jpg (23.87 KiB) Viewed 2319 times

[bdosborn]

My kill a watt gave readings that jibed with my Victron, about 20% more on the KAW than on the Victron (efficiency, etc). I just tried to use it on my new Champion generator and it died when I started the A/C. I don't think they're very accurate or built for surges. I would trust the Trimetric over the KAW.

Bruce

[John61CT]

Same here.

Did you buy the KAW from a reliable source? Might be a fake, otherwise just faulty.

[featherliteCT1]

bdosborn, thanks for the reply.

John61CT, I bought a "P3 International P4400 Kill A Watt Energy Monitor" from Walmart, online. Thanks for the reply.

I bought a small 1.1cu ft freezer that I am converting into a refrigerator for my trailer and was trying to figure out what size inverter I needed to power the fridge. The Killa Watt meter made me think I could use a cheap 400 watt inverter but the inverter was too small to handle the initial surge. The Kill A Watt meter told me otherwise. The fridge does start with a cheap 750 watt inverter. I was hoping to use the smallest inverter I could find to run the fridge. I do not know if a less than 750 watt inverter will start the fridge. However, I just ordered a 700 watt Renogy pure sine inverter for $130. I hope it works!

I guess I will just assume the Kill A Watt unit is inaccurate.

[bdosborn]

We usually figure 7 times running load as a ball park figure for starting requirements. Motors start easier with pure sine wave inverters rather than modified sine wave.

Bruce

[featherliteCT1]

Bear with me, please, as I am still learning.

My Trimetric said that the freezer was drawing 5 amps out of my battery under running load. Using the 7 times multiple would mean that, on startup, the freezer would draw 35 amps x 12v= 420 watts.

Is it surprising that the cheap 400 watt inverter could not handle the 420 watt surge?

[bdosborn]

Not really, starting motors on inverters requires a lot of things to go right:
- modified sine wave means 20% more power required to run motors.
- The wires to a cheap inverter are usually undersized so voltage drop is a problem with big loads.
- I doubt the inverter has much surge capacity, especially if it has an automotive type plug. Those are often limited to 20A because that's what they're typically fused at in cars.
- They often exaggerate the specs on cheap electronics

I have a 300W Morningstar pure sine inverter that ran my electric drill very nicely till all the smoke came out. Doh!
Bruce

[featherliteCT1]

Thanks a bunch ... I will try to remember to report back and let you know if the Renogy 700 watt pure sine inverter works. I am optimistic from what you say.

[bdosborn]

If it were me, I would size the wires to the inverter for 1400 watts, so about 120A.

2 awg cables

Bruce

[featherliteCT1]

Will do with the 2awg

[featherliteCT1]

Update: The Renogy 700 watt pure sine inverter arrived and has no problem running my refrigerator.

Now I am waiting for hot weather to arrive so I can ascertain how the unit will work in elevated temperatures and how many amps the unit will draw in the heat.

Also, my 2000 watt generator has no problem running in eco mode when the unit starts up.

[bdosborn]

Let us know how it the Renogy does over a few camping trips. I'm thinking of upgrading my inverter to 700W so I can run a Keurig machine.

Bruce