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

[gary350]

The small camper trailer refrigerator runs on 2 amps 120 VAC but needs 10 amps 120 VAC to start.

The refrigerator could run on a 250 watt DC/AC inverter and car battery but it requires a 1500 watt inverter to get the motor started.

The 1500 watt inverter wastes power it pulls 6 times more idle amps than the 250 watt inverter with NO LOAD. I am trying to avoid wasted power. My converters are all from Harbor Freight store.

The problem is, How to get the refrigerator to start and run on a 250 watt DC/AC inverter?

 

[Nigel Goodwin]

Buy a proper camping/caravanning fridge, they usually run off 12V or gas.

 

[gary350]

Buy a proper camping/caravanning fridge, they usually run off 12V or gas.

Why would I want 12 volts or gas in an all electric 120 volt AC camper trailer?

Those old 3 way refrigerators cost 4 times more and are 5 times heaver than a new modern 120V refrigerator.

 

[Nigel Goodwin]

Why would I want 12 volts or gas in an all electric 120 volt AC camper trailer?

Because it would solve your problem

Apart from that, you already know the answer - use the 1500W inverter, and waste power (or plug it in to mains, which is what your caravan is intended for if it's all 120V).

 

[tcmtech]

The 1500 watt inverter wastes power it pulls 6 times more idle amps than the 250 watt inverter with NO LOAD. I am trying to avoid wasted power. My converters are all from Harbor Freight store.

Okay I will bite on this one.

How exactly does the solid state 1500 watt inverter draw 6 times more power than the 250 watt one when running a 200 watt load and how exactly have you confirmed this?

Or are you assuming that since it's rated at 6 times the capacity of the 250 watt one that it therefore draws 6 times as much power to do the same 200 watt conversion?

 

[Nigel Goodwin]

How exactly does the solid state 1500 watt inverter draw 6 times more power than the 250 watt one when running a 200 watt load and how exactly have you confirmed this?

I don't really believe it will take six times the current, but it will take more than the smaller inverter.

Perhaps an inverter somewhere between the two would be the best solution?, particularly if you could modify it to slow down the over-current protection.

 

[gary350]

Because it would solve your problem

Apart from that, you already know the answer - use the 1500W inverter, and waste power (or plug it in to mains, which is what your caravan is intended for if it's all 120V).

National Parks have NO electricity at any camp sites. If you already own an all electric 120 vac camper trailer you don't start ripping out things like the new modern high efficiency refrigerator to replace it with an old antique refrigerator. We intend to live in every National Park in the USA starting about February. Most parks have rules against generators. People don't go to National Parks to hear 500 generators running. I was hoping to do this with one 1000 amp battery. Most national parks have too many trees for solar. We want to stay parked a minimum of 2 weeks at each National Park before we move on to the next one.

 

[gary350]

Okay I will bite on this one.

How exactly does the solid state 1500 watt inverter draw 6 times more power than the 250 watt one when running a 200 watt load and how exactly have you confirmed this?

Or are you assuming that since it's rated at 6 times the capacity of the 250 watt one that it therefore draws 6 times as much power to do the same 200 watt conversion?

One thing I discovered my accident is, if I leave my 250 watt inverter connected to the car battery all week but only use the battery 2 to 4 hours a day to run about 100 watts of light bulb the battery is dead in 7 days. The math does not add up??? So I put an amp meter in the circuit between the battery and the inverter, with no load and the inverter turned off it pulls amps. The only way to stop the inverter from running the battery dead when it is not being used is disconnect it from the battery. The big inverter uses about 6 times more amps than the little inverter when its not being used and the switch is turned OFF. Only way to save the battery is disconnect the inverter from the3 battery. Don't ask me why these inverters pull amps when they are turned off I don't know. I have no clue if all inverters do this but I have several 8 year old inverters, 100, 150, 250, 300, 1500 they all pull amps with the switch turned off and they are not all made by the same company. I have no clue what the on/off switch is going, all I know is the LED lights go off, fan goes off, the unit makes no 120 vac with the switch off but it still uses amps from the battery.

 

[Nigel Goodwin]

Inverters DO consume power, and considerable power, even with no load - it's essential to either turn them off fully, or disconnect them from the battery.

Obviously this isn't an option with a fridge, hence my 12V suggestion.

Assuming you have an inverter that can be shut down fully (by a voltage signal), then it could be possible to design some electronics to turn the inverter ON and OFF fully as the fridge requires power.

Probably by far the simplest way though would be to access the fridge thermostat directly, so it turns the inverter ON and OFF as required. If the thermostat is controlling the power to the fridge, then you can permanently connect the compressor, and use a relay controlled by the thermostat to switch the 12V battery to the inverter. However, if you can get an invert that can be easily switched ON and OFF, it would be a more elegant solution.

 

[tcmtech]

The big inverter uses about 6 times more amps than the little inverter when its not being used and the switch is turned OFF.

And these amps add up to to how much of a actual standby full off wattage draw difference?

Reason being what I can find on Harbor Freight inverters is that they are primarily the CenTech brand and the specs sheets for their 250 and 1500 watt inverters show an active on power draw of ~.5 amps and ~2 amps.

Also how are you recharging a battery bank that is that large and why can't it be charged up more often?

 

[gary350]

And these amps add up to to how much of a actual standby full off wattage draw difference?

Reason being what I can find on Harbor Freight inverters is that they are primarily the CenTech brand and the specs sheets for their 250 and 1500 watt inverters show an active on power draw of ~.5 amps and ~2 amps.

Also how are you recharging a battery bank that is that large and why can't it be charged up more often?

I am thinking about putting a 1500 watt generator on the tongue of the trailer and using a car battery charger to charge the battery as we drive down the interstate highway to the next camp ground. I don't mine having generator run behind the vehicle I just don't want one running at the camp ground. Road noise might be louder than the generator. Drive from Yellowstone to Crater Lake will take all day. Most of the drives from 1 NP to the next will be a days drive.

I should probably build my own battery charger to try and get a full charge as quick as possible. One of the worse things you can do to a lead acid battery is not give it a full charge. I need to do more experiment's with this. Lead acid batteries are self regulating, a dead battery will pull a lot of amps but a 98% charges battery will pull very low amps. If it takes 10 hours to charge a dead battery 1/2 charged it will take another 10 hours to charge it another 1/4 charge and another 10 hours to charge it another 1/8 charge. Pretty close to that, this is a simplified explanation.

Here is a solar panel experiment to charge the battery. 9 solar panels in parallel produce 18.4 VDC at 135 watts. Amp meter shows a high amp charge when battery is low, the closer it gets to full charge the lower and lower the amps are to the battery. When battery is fully charged amps are almost zero on the meter. When the inverter is ON I can see how many amps each device pulls from the battery through the inverter. I need to experiment and learn the real life of the battery. I don't know for sure how much power is lost in the inverter but I'm not sure I need to know that all I need to know for sure is how many amps each item pulls and on average how many hours it takes to run the battery low enough to be charged. And how many hours it takes to recharge the battery. 1 volt makes a big difference in the charge rate of the battery. I have a 5KW generator I can experiment with too. For travel I want to buy the smallest generator that will work. Most of the small generators have a small fuel tanks I don't want to stop every hour to put gas in the generator. I need a small generator that will run for 8 hours. My research and development is a bit slow. LOL Going camping again Friday to Sunday. These solar panels are worthless where we go camping tall trees and lots of shade I cant get 1 whole hour of battery charge time per day but the experiment works good at home in the driveway where I can get full sun all day if there are no clouds.

 

[tcmtech]

Yes I am quite familiar with the aspects of charging big battery banks.

Personally if it was me I would just put a high capacity alternator and a set of heavy gauge leads (cheap set of repurposed 2 ga jumper cables) on the vehicle that pulls the camper to charge the battery when driving being a good high capacity commercial type that can put out 145+ amps continuous duty and 190+peak is only around $135 at Napa parts centers. I have put several on our larger farm tractors now and they definitely can handle doing high load work for long durations that most automotive units would cook to death in minutes trying to carry.

What I am saying is I see no point in running a generator to power a battery charger to charge the battery system while you are driving when you have perfectly viable engine for a power source already 15 feet away that can power a high capacity charging system that is capable of way more output and thus far shorter recharge times than a small genset and portable battery charger could ever do.
Especially so when you factor in that at 1500 watts before the battery charger will work out to a 15+ hour run time per recharge assuming you have a automotive battery charger that can supply close to the full 1500 watt output which most only can do a few hundred watts continuous duty.

However if are dead set on doing a genset charging system that's going to be running mostly just to charge that big battery system I would recomend building a dedicated one from a 4 - 5 Hp engine and one of those big commercial alternators.
Being able to throw 140 - 150 amps at that 1000 amp battery system for 7 - 8 hours Vs a few hundred watt battery charger for 30 - 40 hours shouldn't be too hard to figure out where your time and money are better spent.

 

[ChrisP58]

Double check the Amp-hour rating of your battery. Be aware that most automotive batteries are rated in CCA (Cold Cranking Amps.) Finding the real Amp-hour can sometimes be difficult. For reference, a typical auto starting battery might have a CCA rating in the range of 500-700 Amps. But it's Amp-hour rating might only be 50 to 75 Amp-hours. A 1000 Amp-hour battery will be many batteries in parallel. For your application, deep cycle marine batteries would be better than automotive starting batteries, and usually are listed showing their Amp-hour rating.

Many generators targeted for camping and industrial use have a 12 volt battery charging output, in addition to the AC outputs. Though it may not have as many watts at 12 volts as it does at 120 VAC.

 

[gary350]

Double check the Amp-hour rating of your battery. Be aware that most automotive batteries are rated in CCA (Cold Cranking Amps.) Finding the real Amp-hour can sometimes be difficult. For reference, a typical auto starting battery might have a CCA rating in the range of 500-700 Amps. But it's Amp-hour rating might only be 50 to 75 Amp-hours. A 1000 Amp-hour battery will be many batteries in parallel. For your application, deep cycle marine batteries would be better than automotive starting batteries, and usually are listed showing their Amp-hour rating.

Many generators targeted for camping and industrial use have a 12 volt battery charging output, in addition to the AC outputs. Though it may not have as many watts at 12 volts as it does at 120 VAC.

That explained a few things. My battery goes dead sooner than it should according to the math. I figured there must be a very large wasted of power in the DC/AC inverter but....... maybe the problem is the battery rating is not correct? I have learned I can not count on the math being correct. I need to learn how much power is lost in the inverter. I need to learn the true power of the battery.

 

[gary350]

Yes I am quite familiar with the aspects of charging big battery banks.

Personally if it was me I would just put a high capacity alternator and a set of heavy gauge leads (cheap set of repurposed 2 ga jumper cables) on the vehicle that pulls the camper to charge the battery when driving being a good high capacity commercial type that can put out 145+ amps continuous duty and 190+peak is only around $135 at Napa parts centers. I have put several on our larger farm tractors now and they definitely can handle doing high load work for long durations that most automotive units would cook to death in minutes trying to carry.

What I am saying is I see no point in running a generator to power a battery charger to charge the battery system while you are driving when you have perfectly viable engine for a power source already 15 feet away that can power a high capacity charging system that is capable of way more output and thus far shorter recharge times than a small genset and portable battery charger could ever do.
Especially so when you factor in that at 1500 watts before the battery charger will work out to a 15+ hour run time per recharge assuming you have a automotive battery charger that can supply close to the full 1500 watt output which most only can do a few hundred watts continuous duty.

However if are dead set on doing a genset charging system that's going to be running mostly just to charge that big battery system I would recomend building a dedicated one from a 4 - 5 Hp engine and one of those big commercial alternators.
Being able to throw 140 - 150 amps at that 1000 amp battery system for 7 - 8 hours Vs a few hundred watt battery charger for 30 - 40 hours shouldn't be too hard to figure out where your time and money are better spent.

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.

 

[tcmtech]

That explained a few things. My battery goes dead sooner than it should according to the math. I figured there must be a very large wasted of power in the DC/AC inverter but....... maybe the problem is the battery rating is not correct? I have learned I can not count on the math being correct. I need to learn how much power is lost in the inverter. I need to learn the true power of the battery.

Math tends to not lie. Misread and misunderstood component ratings tend to be far more likely the source of the problem.

I was assuming you had a large bank of deep cycle batteries but if you only have one common sized vehicle battery and you are going by its CCA (Cold Cranking Amps)number and not it s AH (Amp Hours) number that's why your numbers are not adding up.

If it's just one normal sized battery then your stock charging system on your pickup should have no trouble recharging it on the go.

 

[Nigel Goodwin]

I need to learn the true power of the battery.

Is it just one battery? - and how many times bigger than a normal car battery is it (essentially the larger the battery the larger the capacity).

 

[MikeMl]

For the battery bank, you need two to four of these wired series/parallel to make 12V.
I have six of them in my golf cart. They ain't cheap, but they will stand multiple deep discharges, while any so called automotive, or even marine deep cycle batteries wont.

Trojan also makes sealed deep-cycle AGM, but I prefer to be able to add distilled water as needed.

What I have learned about lead acid batteries in fifty years of hard knocks:

1. Do not use automotive starting batteries for anything but starting a car. They are designed never to be discharged below ~80% of their Ah capacity.

2. Do not discharge any 12V lead-acid battery below 10.5V. If you do this to an automotive starting battery, it is junk and might as well be replaced.

3. Never leave a lead acid battery discharged for more than a day or so.

4. Always keep unused lead-acid batteries near full-charge when stored which means topping them up at least once a month or continuously with a "smart charger".

5. Never let the electrolyte level drop to expose the plates. Always use distilled water.

6. Use a hydrometer to determine state-of-charge

7. Periodically (every month or so during use) equalize the batteries. Look at **broken link removed** for how to do this.

 

[gary350]

Is it just one battery? - and how many times bigger than a normal car battery is it (essentially the larger the battery the larger the capacity).

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?

4 years ago I bought a 1000 AH battery. It was doing better for the type of camping we were doing then so I never did any testing.

Now we want to spend early part of our retirement living in National Parks for a while. Now I am getting more serious about having a reliable battery system that wont play tricks on us and go dead sooner than it should.

I know parallel batteries will run themselves dead trying to charge each other. If we need 2000 amps it will be best to buy two 1000 amp 6 volt batteries and put them in series and charge the 2 batteries with a 12 volt charger.

I have not yet determined exactly how many amps we need. I need to start acting like I am camping in a National Park in back yard and do some serious tests to see how things work out.

The power companies use high speed switch gear to switch sub stations in our out of the grid fast enough you hardly notice it at home, if you see a tiny flicker of the lights that is probably what it was. 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.

 

[Nigel Goodwin]

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?

Not at all, the rated AH is only under certain very specific circumstances.

4 years ago I bought a 1000 AH battery. It was doing better for the type of camping we were doing then so I never did any testing.

Now we want to spend early part of our retirement living in National Parks for a while. Now I am getting more serious about having a reliable battery system that wont play tricks on us and go dead sooner than it should.

I know parallel batteries will run themselves dead trying to charge each other. If we need 2000 amps it will be best to buy two 1000 amp 6 volt batteries and put them in series and charge the 2 batteries with a 12 volt charger.

Have you checked the prices of such things?

**broken link removed**