# Tri-metric

Solar Expert Posts: 66 ✭✭
Have a situation, hope someone can explain. My Tri-metric working fine and showing a draw of only 2+ amps, phone and TV satelite reciever. Then I plugged in a 900 watt vaccum that should have seen an additional draw of 7.5amps, but instead the Tri-metric showed 77 amps in total. Disconnected system and tried again, same thing, had no time to play with it, had to leave cottage. Any suggestions for when I get back to take a closer look? System is: VFX2812,Hub,Mate,MX60,3-4Volt, 1104amp/hr Surrettes.

• Solar Expert Posts: 5,433 ✭✭✭✭
Re: Tri-metric

My guess is that the vacuum draw of 900 watts is the rated max draw not the average running draw. Most motor loads draw much higher amperages at start and under load. The rating plate would show the largest expected draw.

I have found the trimetric to be very accurate.

Icarus
• Solar Expert Posts: 705 ✭✭
Re: Tri-metric

The reading is correct your Tri Metric is reading DC current draw from the batteries to the inverter. A 900 watt vacumn will draw 7.5 amps ac of power on a 120v system. The DC side (batteries) needs to supply at a factor of 10 not including losses to match this AC load hence 77 amps draw of Dc Current. Your Tri Metric is reading correctly.

A 24 volt DC system would draw approximately half the current or 38 amps for the 900w vacumn compared to your 12 volt system
A 48 volt DC system would draw approximately quarter the current or 19 amps compared to your 12 volt system

Assuming no internal conversion losses and the AC voltage is always 120 v

Power (Watts) is Volts x Amps

HTH
Re: Tri-metric

Unless I am missing something, 77 amps sounds about right for a 12 volt battery bank...

77amps * 12 volts = 924 watts

7.5 amps * 120 volts = 900 watts

The battery monitor is measuring the 12 volt current of your battery to the inverter, not the 120 volt circuit out of your inverter to the vacuum cleaner.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 66 ✭✭
Re: Tri-metric

Thanks to all, solar is sure one Big, learning experience.
• Solar Expert Posts: 66 ✭✭
Re: Tri-metric

After absorbing the imformation given, am I correct in thinking that all my calculations for a draw on a 12 volt system should be muliplied by 10, ie. 120volt appliance draws 13 amps, but actually reduces my battery bank by 130amps and so on. If my battery bank is 1104 amp/hr in total, 550 amps are useable to keep above 50% discharge. As you can see I am very new at this.
• Solar Expert Posts: 5,433 ✭✭✭✭
Re: Tri-metric

Duh!!!

I spaced on the 12vdc versus the 120 vac! It is indeed about a 10/1 conversion.

I did the same thing when I installed my inverter. I fused it for 15 amps on the DC side, and couldn't figure out why I kept blowing the fuse with 300 watt ac load! (2.5 amps @120 volts, 25 amps @ 12 volts!)

Sorta makes my previous post look pretty silly!

Icarus
Re: Tri-metric

Yep... You are getting it... Now, 10:1 is a pretty easy ratio to make estimates with, but it can be worse:

[120 VAC / 10.5 VAC (min-12 volt design)] * 1/85% (inverter efficiency)=13.4:1 current ratio...

Also, many batteries are rated at 20 hour discharge rates... When you increase the drain, the efficiency of the battery goes down quite a bit too...

Take a look at the Wind-Sun Battery FAQ and see the difference in apparent capacity at 100 hour, 20 hour, and 8 hour rates.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 705 ✭✭
Re: Tri-metric

Stick with the 10/1 ratio its good enough for in head calculations, hey your trimetric showed it at 10/1, real life, if we followed all the maths all the time we wouldnt have time to watch the TV:p
• Solar Expert Posts: 66 ✭✭
Re: Tri-metric

Thanks to all for your assistance, this is such a great web site.
• Solar Expert Posts: 66 ✭✭
Re: Tri-metric

Back with another question, when last at cottage noticed that when my inverter was on the Tri-Metric charge indicator light would go off, but as soon as I turned inverter off the light came back on, volts, amps and Battery Full indicators all seemed to still work OK, any thoughts.