How to run a 2 amp 120 VAC refrigertor on DC/AC inverter.

[MikeMl]

...

I know parallel batteries will run themselves dead trying to charge each other. ...

Not true. OWT! It is done all the time in solar systems. The batteries do have to be of the same type and capacity.

 

[MikeMl]

I had one 650 AH battery. When the math says I pulled 350 amps out of the battery then the battery is dead something is not right?...

You are not consistent with your math or units. Do you mean you pulled 350Ah out of the battery?

The battery maker provides the information on how long you can expect the battery to deliver a given current on its data sheet. For example, look at the T105 I linked to earlier. Note that although it is advertised as being a 225Ah battery, it will deliver 25A for 447min ( 186Ah) or 75A for 115min (143Ah) at those stated discharge currents. To get the rated 225Ah out of it, it would have to be discharged at a rate of less than 22A; also, read footnote B...

To deliver 2A @120Vac (=240W) through an inverter that is ~80% efficient would require a draw of 300W from the battery bank, which is current draw of ~24A.

 

[tcmtech]

That is a good idea. I just never considered that because I know the alternator drive belt is sized for the alternator that is on the vehicle. If I double the power of the alternator it will require 2 times more HP to run the alternator and the existing belt wont be sized to deal with 2 times more belt friction and 2 times more belt stress. Also vehicle wiring wont be sized for 2 times more amps but it should not need more amps so that should not be a problem. Maybe there is something I don't understand about this yet? It wont be a big deal to run wires from the alternator to the camper battery. My son is a certified automotive technician I need to talk to him about this.

It would be really helpful to know what type of vehicle you are pulling your camper with. You know, Brand Model Year. That sort of stuff.

As for the belts I would not worry about them too much. The actual mechanical load differences between a stock 100 amp and aftermarket 150 amp are not huge and can easily be adjusted for by putting a slightly larger pulley on the bigger alternator to slow it down a bit and give the belts more mechanical advantage if they start showing obvious signs of needing it after the higher capacity alternator is put on.

Most commercial application alternators are rated for their full output at 3600 - 4000 RPM (many even less) whereas most automotive ones are rated for theirs at 6000+ RPM.

 

[tcmtech]

This gives me an idea how to start my refrigerator with a 1500 watt inverter then switch over to 250 watts to keep it running. The refrigerator has automatic cycle so the inverters need to re-set every time the refrigerator turns off.

You would probably just be better off using the refrigerators thermostat to turn the whole inverters DC side power on and off with either a relay or through its existing power switch as needed. It would greatly simplify things.

Personally at this point I have seriosus doubts the inverters are the problem with the run time issue. Lack of proper understanding of battery ratings and the resulting use of an undersized battery is likely where your whole problem is coming from.

I suspect as other have that either you misinterpreted the CCA number for AH capacity or your have a grossly over rated battery being as Nigil has shown in his link a reall 1000 AH 12 volt battery system would be the size of two large suitcases and weigh several hundred pounds which if your battery system is only made up of one single automotive type battery you only have ~100 AH and ~1200 maximum watt hours of energy available not 1000 Ah and 12,000 watt hours of energy available..

Given that what is the physical size of your battery being the largest commonly available 12 volt deep cycle batteries I know of are the 8D group size which are about 20 inches long 11 inches wide, 12 inches high and weigh in at around 140 pounds or more and they have a AH rating of maybe 250 at best.

My point is some actual names and model numbers from your equipment would greatly help in figuring out where your problem is and how to design something better.

 

[debe]

Been down this road my self using a household fridge on an inverter camping. Its very inefficient way of doing things. I now use a Waeco 80L 12vdc fridge which uses a Danfoss BD35 compressor. If theres enough sunlight in a day my 120W Solar panel will keep the battery charged. This is how most campers here in Australia do it.

 

[iouae]

Could you tell me if this is a stupid idea or not.
Suppose you had both inverters attached to the batteries via a DPDT switch or relay. This relay sits on the 12V lines.
You could turn on the 1500W inverter first for a few seconds to get the fridge motor running.
Then throw the DPDT switch or relay to switch off the big inverter, and on the smaller inverter.

And a microcomputer could take over control of the relay. It could even monitor the temp of the fridge so that one could turn the fridge up to max coldness and not worry about the fridge turning on or off, since this would be controlled by the uC.

Would there be an incompatible phase problem as one swops from one AC source to another?

 

[tcmtech]

I don't think that Gary350 has that level of skill sets and understandings of electronics to pull something like that off.

So far he has yet to give us the basics of what brand and model battery he is using or anything else like the inverters actual amp draws when running the refrigerator or anything else anyone has asked for so that we can find the problem with the math that he says does not add up.

 

[iouae]

I have 400W of solar panels, a 1oooW inverter, an 80W deep freeze and one 50Ah car battery.

To run the deep freeze puts such a strain on the little car battery and inverter at startup.
My plan was to use mains to start the deep freeze running, and then using the DPDT to switch over to the solar driven battery powered inverter.
(I know the answer is to have a mains connected inverter, but I don't have one).

I did wire up a DPDT relay, and tried it out on a 100W incandescent lamp swoping from 220V mains ac to another 220V mains ac.
It worked fine for the lamp with barely a flicker.

I have been too scared to try it on the inverter/fridge/mains setup although I am sure it would work. But the cost of inverters being astronomical, I have postponed testing it indefinitely.

That is why I was suggesting that it would be similar to swoping between two inverters.

 

[tcmtech]

I have 400W of solar panels, a 1oooW inverter, an 80W deep freeze and one 50Ah car battery.

To run the deep freeze puts such a strain on the little car battery and inverter at startup.
My plan was to use mains to start the deep freeze running, and then using the DPDT to switch over to the solar driven battery powered inverter.
(I know the answer is to have a mains connected inverter, but I don't have one).

I did wire up a DPDT relay, and tried it out on a 100W incandescent lamp swoping from 220V mains ac to another 220V mains ac.
It worked fine for the lamp with barely a flicker.

I have been too scared to try it on the inverter/fridge/mains setup although I am sure it would work. But the cost of inverters being astronomical, I have postponed testing it indefinitely.

That is why I was suggesting that it would be similar to swoping between two inverters.

I would either just get a bigger properly designed deep cycle battery or grid tie the solar panels (DIY pirate grid tie is surprisingly cheap and easy to do and I have a number of threads on it in the RE section here) and put their power directly to your AC mains and skip all the battery and inverter plus switchover nonsense all together.

As for the 50AH car battery if it can't handle the short term higher current draw that a 1000 watt inverter running a 80 watt freezer can pull (~40 - 50 amps from what should be a 500 - 750 CA rated battery) it's already past the end of its useful life.

 

[gary350]

I have not checked prices of solar batteries. I think solar batteries must be over priced to make the sellers a ton of money. Some fork lifts use batteries in parallel, golf carts have a lot of batteries, some old tractors use 2 low voltage batteries in series, some construction equipment have batteries in series too. So far I have only checked 6 volt batteries at 2 different auto parts stores.

 

[Nigel Goodwin]

I have not checked prices of solar batteries. I think solar batteries must be over priced to make the sellers a ton of money. Some fork lifts use batteries in parallel, golf carts have a lot of batteries, some old tractors use 2 low voltage batteries in series, some construction equipment have batteries in series too. So far I have only checked 6 volt batteries at 2 different auto parts stores.

That's your problem there, you're looking at car batteries - a very poor choice for what you want to do - you're also unlikely to find 1000AH batteries in auto parts stores.

 

[MikeMl]

I have not checked prices of solar batteries. I think solar batteries must be over priced to make the sellers a ton of money. Some fork lifts use batteries in parallel, golf carts have a lot of batteries, some old tractors use 2 low voltage batteries in series, some construction equipment have batteries in series too. So far I have only checked 6 volt batteries at 2 different auto parts stores.

The kind of batteries you need do not come from an autoparts store.

 

[tcmtech]

I have not checked prices of solar batteries. I think solar batteries must be over priced to make the sellers a ton of money. Some fork lifts use batteries in parallel, golf carts have a lot of batteries, some old tractors use 2 low voltage batteries in series, some construction equipment have batteries in series too. So far I have only checked 6 volt batteries at 2 different auto parts stores.

Putting large 12 volt batteries in parallel is done all the time. Yes larger machines used to use 6 volt batteries in series but nowadays the most common thing is to use two three and four large 12 volt batteries all paralleled together. I know that for a fact being I have worked around heavy equipment and large trucks all my life and have spent a huge amount of time working specifically with these machines starting and charging systems.
To be honest almost every diesel pickup or car with an engine larger than an inline 4 cylinder uses two 12 volt batteries in parallel as well.

The only time that one battery discharges the other is when that battery is bad and that is why when one goes bad its the best practice to replace all the batteries opposed to just the single one but ion many cases that is not necessary either if the other batteries have been properly tested and are still good.

If you are going to be shopping around the auto parts places for batteries I would highly recomend going with the Marine Deep Cycle type or the AGM deep cycle which most of those places do carry if you ask them about them.

I know for a fact that Napa stores can get 12 volt 230 AH 8D size AGM severe service deep cycle batteries. Granted they cost $500 - $600 each but they are a huge and extremely durable battery.

 

[gary350]

We found this Alto Safari Condo F series parked next to us at the camp ground this weekend. WOW this is exactly what we want. Small table for 2 in the front that can be made into a small bed. Queen bed in the back. Toilet and shower. Kitchen. Heat and AC. Propane, 240 vac hook up, solar panels and 12 volt battery. Trailer weighs 1592 lbs. The people pulled it with a small Honda Pilot V6 engine. They said it pulls 70 mph on the highway like its not back there. Price $30,000. and it takes 2 years to get one............2 years? That sucks.

https://www.safaricondo.com/en/caravanes

 

[tcmtech]

So given your misjudgment of the size of your battery should we assume you are misjudging the size of this camper and assume it's really just a Dodge minivan with a Barbie playhouse in the back seat?