Reducing refrigerator start up current

I mentioned my 1000w inverter built in low voltage alarm 'bleeping" when my house batteries got down to ~12.5 volt lever.  Gary Brink had some insight on this (post in Boondocking).  So........not letting not knowing anything about electronics stop me I went back to see if I could reduce the start current that causes the few millisecond noise coming from my inverter every time the refrigerater starts.  My refrig is an inexpensive 3.2 cf Igloo that I modified (reduced its power consumption) for boondocking.  Not a lot of $$$ risk in screwing around.  After some confusing and conflicting recommendations and advice on the internet I took the risk and installed a Supco 3'N 1 Start RCO810 solid state start capacitor.  My cheapo refrigerator did not come with a start capacitor.  So my refrigerator upgrade pushed its cost from $100 to $115.

Refrigerator as received:  8.42 amps start, 0.62 amps run.  Measured with a clamp on amp meter.

Refrigerator after adding the RCO810:  5.32 amps start, 0.62 amps run.  Again measured with same clamp on amp meter.

We will be boondocking soon for a few days and hopefully see the improvement in inverter performance when running off of the house batteries and able to go longer before having to recharge the house batteries.

Any comments or insights??

Len and Jo said:

I mentioned my 1000w inverter built in low voltage alarm 'bleeping" when my house batteries got down to ~12.5 volt lever.

Click to expand...

12.5 is a fully charged 12v battery.

Actually, it is  12.6v that represents a full charge.

Sounds promising, Len, so let us know how it works out.  A bigger AH capacity battery is another simple way to handle the start-up load. Battery voltage drops in proportion to the amp load, so a larger battery usually doesn't suffer quite so much drop under that initial demand. That assumes adequate connections and wire size, though.

Gary:

It bugged me that I could find no schematic for the device.  I was just installing a black box of "trust us we have been in the business a long time".

I really do not have room in my B for more/larger batteries.  I might be able to mount some UNDER the van but I have no desire to be raising and lowering batteries there.  I am going to review wire sizes this fall when it gets time to put the van back in storage.  Going to '0' size does not look that expensive or cumbersome and I back of napkin estimate that I could get 0.1 to 0.2 less voltage drop with that size.

Skateboard:

Attached are some charts and graphs that I use for house battery charge level for my rig.  I have two Costco (Interstate) 6v Golf Car batteries.  All numbers are approximate...even Interstate has different values in different flyers.  My nominal battery draw is less than 5 amps so I do not use the "standard" 20 amp draw down curves.  What shown agrees ~ with Gary's comment.  Also the problem "beep" isn't with the nominal battery voltage but the voltage the batteries drop to when the refrig momentary start voltage draws them down.

Len and Jo said:

I mentioned my 1000w inverter built in low voltage alarm 'bleeping" when my house batteries got down to ~12.5 volt lever.  Gary Brink had some insight on this (post in Boondocking).  So........not letting not knowing anything about electronics stop me I went back to see if I could reduce the start current that causes the few millisecond noise coming from my inverter every time the refrigerater starts.  My refrig is an inexpensive 3.2 cf Igloo that I modified (reduced its power consumption) for boondocking.  Not a lot of $$$ risk in screwing around.  After some confusing and conflicting recommendations and advice on the internet I took the risk and installed a Supco 3'N 1 Start RCO810 solid state start capacitor.  My cheapo refrigerator did not come with a start capacitor.  So my refrigerator upgrade pushed its cost from $100 to $115.

Refrigerator as received:  8.42 amps start, 0.62 amps run.  Measured with a clamp on amp meter.

Refrigerator after adding the RCO810:  5.32 amps start, 0.62 amps run.  Again measured with same clamp on amp meter.

We will be boondocking soon for a few days and hopefully see the improvemeent in inverter performance when running off of the house batteries and able to go longer before having to recharge the house batteries.

Any comments or insights??

Click to expand...

First yes it will start faster with a start cap but it will not reduce the start current it will make it faster, I don't think your meter is fast enough to pick up and measure true start current. Very rarely will you find a start cap on a refgerator no matter what the cost. Starting faster won't make that much difference whe it comes to battery life, I think you need more battery reserve.

Denny

I've often wondered if you could install a supercapacitor right at the inverter's 12 volts DC input to keep the voltage up during the refrigerator's  starting surge.

If a supercapacitor can eliminate voltage sags caused by the power draw of a 1500 watt car audio system during those neighborhood rattling bass thumps, it should be able to do the same during a refrigerator's starting surge.  The cause is the same in both cases - voltage drop caused by the battery's internal resistance plus the resistance of the cables going to the batteries while trying to draw a hundred or so amps of peak current.  Putting the capacitor right at the inverter's input terminals eliminates both of these problems.

Supercapacitors and ultracapacitors are getting cheap - a capacitor bank capable of storing enough energy to crank a car engine may be overkill, but if you want to experiment Ebay has numerous choices.  60 farads of storage (360 farads /6) can deliver over 250 amps of peak current for a second or two.

Or try a conventional car audio system supercapacitor with 2 to 20 farads of storage:

http://www.ebay.com/bhp/audio-capacitor

To get a true perspective of the size of these puppies, note that capacitors are usually rated in milli (.001) or micro (.000001) farads.

They should be treated like any similar capacity battery - protect the terminals against accidental short circuits and put a catastrophic fuse in line with the output.  And follow the instructions to use the supplied series resistor to charge the bank before installing.

rvpuller said:

First yes it will start faster with a start cap but it will not reduce the start current it will make it faster, I don't think your meter is fast enough to pick up and measure true start current. Very rarely will you find a start cap on a refgerator no matter what the cost. Starting faster won't make that much difference whe it comes to battery life, I think you need more battery reserve.

Denny

Click to expand...

I had a thought, were is your inverter mounted? If it's close to the refigerator and not the batteries you may be getting voltage drop on the 12V wires, always mount the inverter as close to the batteries as possible.

Denny

1. Did try capacitor but negative results...only used a 800uf..I think..no noticeable affect

2. Inverter is 4ft of wiring from house batteries.  If I went to '0' size wiring might save 0.10-0.20 of voltage drop. Still considering that though

3.  Good news batteries down to 12.3 volts nominal last night but refrig when it kicked on DID NOT trigger the inverter low voltage alarm. So adding the N '3 did have positive affect. Did not let batteries go lower because did not want to risk inverter "bleeping" every 15 minutes during the night

4.  My 200 watt solar kit I installed 2 years ago did not come with connectors for parallel wiring the panels.  I installed a pair of 'Y' connectors yesterday..... Wow what a difference in this high % shade area. In past would get ~20w....now ~60+watts when sun hits panel(s)

5. Will try "bleeping" test again when batteries get low earlier in the day

Cheers!!

I'm not surprised an 800uf capacitor didn't have any effect - that's 0.0008 farads.  The inverter itself probably has at least that much storage inside it - the internal capacitors charging up is what causes the spark when you first connect voltage to it.

I was speculating about adding several orders of magnitude more storage right at the inverter.  Capacitors of this size have only been available for a couple of years.  Even a relatively small 2 farad car stereo capacitor stores 625 times more energy.  Not to mention the 60 farad car starting capacitor bank.

Lou

I will try ~2 farad some time in future.  Thanks

Bottom Line:

Adding the Supco 3'N 1 Start RCO810 to my 3.2cf Igloo refrig did reduce the Xentrex inverter lowered alarm bleeping problem.  The nominal house battery voltage where the alarm bleeping starts went from 12.50-12.55VDC to 12.22VDC.  Now I can discharge the house batteries all the way down to 12.23VDC without getting the bleep noise every time the refrig turns on.  In the fall if I change over my battery wiring from 4 ga. to 0 ga I might be able to improve on that by another tenth of a volt and at 12.12VDC would be a ~50% discharged battery and a low voltage warning would be appropriate.

SkateBoard said:

12.5 is a fully charged 12v battery.

Click to expand...

Actually, Trojan lists 12.73V as 100% charged

xrated said:

Actually, Trojan lists 12.73V as 100% charged

Click to expand...

Yes, and Interstate list 12.96 volts (indirectly) in one of their PDF's  Me thinks all of them should list voltages to one decimal place instead of two.

And none of those voltages mean much unless the battery is disconnected from all loads, i.e. completely at rest and after surface charge is removed. If you glance at your battery gauge/ammeter while the RV is in use, odds are the observed voltage is at least 0.1v lower than the tables show for the same actual SOC level. It takes very little current draw to drop the voltage.