Talk About Inverters

In talking about killing your batteries with electronic accessories it can very much depend. I have a company Volvo with 3 batteries, they don't like to run anything for very long without the truck running. I did get one of those cutoff thingys for my 12v fridge, it will shut off when it sees the voltage drop too low for fear of draining the batteries below starting capacity.

It also depends on the condition of the batteries - I was having big problems with mine, had to be jumped/pulled/roadserviced 3 times before they sprung for some new batteries. One was at 12 CCA, another around 100, and the third about 400 (should all be around 750). But the voltmeter on the dash would read 12-13v. So the volts can't be entirely trusted.

 

You pay extra for any brand name. But Cobra makes a good inverter. Good enough for a trucker's needs. There's better ones out there like for marine applications, but you pay for them too. A good inverter duplicates household current as close as it can to a 60 hertz sinewave. The bigger Cobra's do that.

If you ever hook a clock to one, it will run slow. That's because they use the 60 hertz AC cycle to time the clock.

 

New charged batteries should run a fridge and TV 8 hours. I have 6 batteries so if you have less? This is where an APU comes in handy.

You could leave a little bunk light on. When the trucks low voltage activates and shuts that light off you know it's time to start the truck up and charge the batteries. The bigger Cobra's have a digital volmeter and watt meter display. I like statikuz idea too.

 

G'day all, I use to have a marine service shop that we installed countless inverters in. Here are some basics on battery life and how a inverter will use that power. We normally calculated how big we need to build the battery bank on a boat. In a trucks situation you have a predetermined bank so you need to kind of reverse engineer ..... figure out what you can run with what you have to work with before you tap your juice or set off the sensor. The examples below are kind of dry to read but will help if your interested.

How Long Will my Batteries Last?
Unfortunately, this question cannot be answered without knowing the size of the battery bank in a truck and the load to be supported by the inverter. Usually, this question is better phrased as "How long do you want your load to run?", then
specific calculations can be made to determine the proper battery bank size and compare it with what you have.

Formulas and Estimation Rules
1. Watts = Volts x Amps
2. Battery capacity is expressed by how many Amps for how many hours a battery will last - Amp-Hour (A.H.) capacity
3. For a 12-Volt inverter system, each 100 Watts of the inverter load requires approximately 10 DC Amps from the battery
4. For a 24-Volt inverter system, each 200 Watts of the inverter load requires approximately 10 DC Amps from the battery.

The first step is to estimate the total Watts (or Amps) of load (i.e laptop,phone charger, IPod, micro) and how long the load needs to operate. This can be determined by looking at the input electrical nameplate for each appliance or piece of equipment and adding up the total requirement. Some loads are not constant, so estimations must be made. For example, a full-sized refrigerator (750-Watt compressor), running 1/3 of the time would be estimated at 250 Watts-per-hour or micro as someone above cited.

After the load and running time is established, the battery bank size can be calculated. The first calculation is to divide the load (in Watts) by 10 for a 12-Volt system or by 20 for a 24-Volt system resulting in the number of Amps required from the battery bank.

Example of Load Calculations
Suppose you were to run a microwave oven for 10 minutes a day, which draw about 1000 Watts, despite their size. To keep it simple, think of the inverter as electrically transparent. In other words, the 1000 Watts required to run the oven come directly from the batteries as if it were a 12 VDC microwave. Taking 1000 Watts from a 12-Volt battery requires the battery to deliver approximately 84 Amps. (1000 Watts ÷ 12 Volts = 84 Amps)

A full-sized refrigerator draws about 2 Amps at 120 Volts AC. By multiplying 2 Amps x 120 Volts, you find out the refrigerator uses 240 Watts. The batteries will need to deliver 20 Amps to run the refrigerator (240 Watts/12 Volts = 20 Amps). Typically, refrigerators operate about 1/3 of the time (1/3 "duty cycle"), or 8 hours a day. Therefore, the A.H.drain will be 160 A.H. (8 hours x 20 Amps = 160 A.H.). After the load and running time is established, the battery bank size can be calculated. The first calculation is to divide the load (in Watts) by 10 for a 12-Volt system or by 20 for a 24-Volt system resulting in the number of Amps required from the battery bank.

 

I've read that several companies will allow hard wired inverters, but want their people to install them.

 

thats some good maths, lucky enough for me after asking the company im hopefully going to today they said 95% of their trucks have apu's. i like those odds.

 

Thanks BNR, gotta do something waiting on the recruiter

 

That way, they are installed properly.

 

Yeah that's what I was getting at. Seem to have forgotten to add that part.