Running dorm fridge with inverter - Page 3 - Fiberglass RV


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Old 03-30-2013, 01:54 PM   #29
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Update. I finally decided to upsize my inverter. Had a nice chat with the Samlex tech support guy, he said my 600 watt was very marginal at best to start a small fridge. When I tried the larger capacitor (above post) I noticed a sticker on the motor that said 8.4 LRA. That's locked rotor amps and means it will draw 1000w the moment of start up.

He and I agreed a 1500w unit would be best as that would provide a little headroom for other loads too. I stayed with a true sine wave model as that is about 30% more efficient when I driving a motor. I want to have the fridge work for a couple of days of dry camping so the efficiency is important to me.

A tip of the hat to Samlex, they answered the phone right away, had lots of helpful advice and even agreed to take back my old 600w unit as a credit toward the new one.

The new unit is currently in route. I'll update again when I get it installed.
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Old 03-30-2013, 02:12 PM   #30
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Quote:
Originally Posted by MCDenny View Post
Update. I finally decided to upsize my inverter. Had a nice chat with the Samlex tech support guy, he said my 600 watt was very marginal at best to start a small fridge. When I tried the larger capacitor (above post) I noticed a sticker on the motor that said 8.4 LRA. That's locked rotor amps and means it will draw 1000w the moment of start up.

He and I agreed a 1500w unit would be best as that would provide a little headroom for other loads too. I stayed with a true sine wave model as that is about 30% more efficient when I driving a motor. I want to have the fridge work for a couple of days of dry camping so the efficiency is important to me.

A tip of the hat to Samlex, they answered the phone right away, had lots of helpful advice and even agreed to take back my old 600w unit as a credit toward the new one.

The new unit is currently in route. I'll update again when I get it installed.
Great follow up. Thanks for completing the story.

I'm impressed with the service from Samlex in this age of labyrinthine telephone menus that usually end up hanging up on you.
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Old 03-30-2013, 03:48 PM   #31
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I stated that my Ramsond is 1500/2000surge. It is actually 1500/3000 and the inverter is happy with a hot start to "ON." It is not happy with a hot start to midway (4) on the dial. I have optimized the solar panel leads to my battery this winter and want to do some more duration tests this spring when the sun gets higher. I have never gone beyond 10 hrs. (cool down on shore power and no solar) with the battery discharge limit at 12.2V. 1.5 amps (15amps DC) running means my 100amp hr. battery SHOULD only allow approximately 3-1/2 hrs. run time. I've done 16 with daytime solar charging in high summer. Obviously, the insulation factor is good enuf to avoid running full time. I don't know how much better I can expect to do. It has worked great on tow vehicle alternator current getting from one hookup site to another. At least I have a refrigerator (rather than a chiller)when I have hookups and an old Coleman ice chest when I don't. I also have the RM2202 if I should ever decide to stand it on its head for decrystallization.

Please give us some numbers when you're up and running, Denny.

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Old 03-30-2013, 03:55 PM   #32
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Will do. I've got a 220ah battery bank so I believe I can get a couple of days.

I also have a victron battery meter so I can see the actual amps consumed.

Looks like the new inverter will be here Mon or Tues and I hope to get in quickly. We are still camping until mid April so l can give it a workout right away.
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Old 04-11-2013, 10:11 PM   #33
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Well, here's the rest of the story.

The 1500w inverter beeped every time the fridge started and sometimes wouldn't start it at all. I noticed the overload light was not coming on, just the alarm tone noise. Finally read the manual very carefully and realized a beep without the overload light meant low voltage on the 12v side, not overload as I had incorrectly assumed. My battery meter showed 12.8v with no load but less than 11v when the inverter was drawing 85 amps. The 12v cables are 4 gage and the manual calls for 1/0 for runs of 4' or less so I first thought the wire was undersized causing the voltage drop. I checked a wire size calculator though and it showed I should should only see a 2% drop at that amperage with my 4 gage wire.

I then thought I might have a bad connection and removed, sanded and retightened the connectors one at a time. Son of a b..., I had a loose battery connection. Tightened it up and the inverter works like a charm. I put the old 600w unit back in and it starts the fridge perfectly. Don't I feel stupid for overlooking such a basic fault! Since the 12v system worked fine with low loads like lights and the inverter powering phone and computer chargers I figured it must be good. Wrongo!

I've run the fridge now for 24 hrs starting with a fully charged 220 ah bank. Started the test in the afternoon with a warm empty fridge (at least 90 degrees in the trailer), low was around 65 at night and a high of 80 today. The fridge plus inverter overhead drew 69 ah, meter indicated 71% of battery capacity was left. This gives me a conservative two day run time on battery alone. If I dry camp with my Honda generator, two hours a day charging will take care of 24 hours of refrigeration.

Over the course of the winter we have had several 4 to 8 hour drives and now that the inverter works, we can keep the fridge cold while on the road. Even 4 hours without power will cause the frost on the freezer compartment to melt.
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Old 04-12-2013, 06:20 PM   #34
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Update after 48 hours:

I noticed at about 46 hours a very short low voltage beep when the fridge kicked on. With inverter draw of 9 amps voltage was down to 11.8 volts. 12.1 with no load.

At 48 hrs fridge was still starting fine. Usage over 48 hrs was 133 ah. Victron meter said 45% state of charge. Turned it off and started recharging the battery.

BTW, this means the fridge was actually running 1/3 of the time.
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Old 04-12-2013, 06:26 PM   #35
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Interesting.
Should the stock Snoozy run the fridge on battery as set up
or did you make certain changes on yours?
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Old 04-12-2013, 08:42 PM   #36
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Denny, should I be taking an offline voltage reading rather than shutting down at 12.2V while under load? Maybe I've short changed myself on runtime tests. Could I assume that 11.8V under load would correlate to 12.2 without?

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Old 04-12-2013, 10:05 PM   #37
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Interesting.
Should the stock Snoozy run the fridge on battery as set up
or did you make certain changes on yours?
I think the stock Snoozy has a GP 24 battery? Maybe 60 or 80 ah capacity? Not sure but you could check yours.

I have two 6v 220 ah golf cart batteries and a 30 amp Iota charger. If the stock battery is one third my capacity it would run the fridge a little less than one third as long.
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Old 04-12-2013, 10:22 PM   #38
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Denny, should I be taking an offline voltage reading rather than shutting down at 12.2V while under load? Maybe I've short changed myself on runtime tests. Could I assume that 11.8V under load would correlate to 12.2 without?

jack
It's tricky correlating voltage to charge state. To use the theoretical voltage vs charge state relationship, you should let the battery 'rest' for a couple of hours before taking a voltage measurement at the battery terminals. Measuring voltage under load introduces ankther variable as the greater the current the lower the voltage will be no matter what the state of charge is. The only practical way I know is to measure the current flow with a meter like the Victron, Link 10, etc. The Victron is the best as well as least expensive but it's still around $150.

The voltage will differ depending on where you make the measurement. The battery terminals will always show a higher voltage than further downstream due to the resistance of the wires and connectors. Wire and connector resistance is a function of current so they will have almost no effect on voltage with little or no load but can have a big effect with large amp draw.

With my slightly loose battery connector there was no significant voltage drop when drawing a few amps to run the lights or charge the computers but a two volt drop (18%!!) at 85 amps running the inverter with a hair dryer as the 120v load.
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Old 04-14-2013, 01:07 PM   #39
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Unpredictable chemistry? I'll say. Thanks for the eval, Denny. Some more tests coming soon for my rig.

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Old 04-14-2013, 02:13 PM   #40
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Some of the battery monitoring tools mentioned by Denny:
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