Refrigerators, Start-up Surge and Inverters, oh my!

[kazetsukai]

Originally Posted by Simplicity

I just ran across this Cotek 3000 LF inverter charger https://www.solar-electric.com/cotek...-inverter.html.

I think I remember seeing this brand name mentioned, but I've not heard must about them.

Any input would be appreciated.

For that price, I'd say go with a Victron MultiPlus of a similar rating. It will handle the shore power side of the equation as well, and offers bluetooth connectivity (via a dongle)/etc.
https://www.solar-electric.com/victr...0dac01f064aba8


EDIT: May need something else if you're doing split phase/120/240.
EDIT2: You'd need the Victron Autotransformer in addition to a MultiPlus.

[atthebeginning]

Steve,
I would consider speaking with the people at AmSolar in Oregon. I told them what appliances I anticipated using, 30a or 50a bus, lithium or other, solar, generator, alternator or shore power. We worked out a system. I bought the components and installed it myself. It has worked flawlessly as expected. Their support has been OUTSTANDING, even with a 911 call out on the road. My bad not theirs. I dodged a bullet and sold an inv/chg on eBay and went with an all Victron system. My lithium batteries are LifeBlue.
Good luck.

[Doktari]

Some great contributions in this thread. I was in a hurry to leave for Arizona and had a used fridge I’d never tried before, and batteries I’d not tried. I decided to go with a load-shedding option and am trying a adjustable LVD (low voltage disconnect) on my fridge circuit. If I’m cooking with my induction plate or heating water in the kettle or hot water heater the voltage is dawn down and the fridge won’t try to start. It seems to be working good as those other loads are only on for a short while and my fridge can return to normal working operation after a few minutes. I have a 2100 watt inverter and only a 200ah battery so the voltage can sag quickly with big loads. The water heater has a knob to control it manually. I don’t want it to come on while I’m cooking with the induction plate. My inverter makes a loud humming noise if I forget to turn down the water heater and start cooking ( and the voltage plummets quickly). I could put a LVD on the water heater too but only had ordered one. The manual control works pretty good. And then the inverter has a loud beep and shut down at 10.5 volts but I have only ever done that once. So at least I know it works.
The LVD was inexpensive on Amazon. Who knows if it will last long.

[Simplicity]

Kaz - I'm doing a simple 30amp / 120v into an inverter/charger to as few batteries as I can to run the components I've listed. If I'm understanding what your edit comments were about only apply if I was doing split or 240. So, all I'd need is the Victron inv/chrg you suggested. Am I interpreting all that correctly?

InTheBeggining - Thanks for the lead. You're basically seconding Kaz's Victron recommendation. Since I'm in WA., and if all goes well with my tranny modulator, it might be a good reason for a road trip to OR..

My search continues!

[Simplicity]

Originally Posted by Doktari

I decided to go with a load-shedding option and am trying a adjustable LVD (low voltage disconnect) on my fridge circuit. If I’m cooking with my induction plate or heating water in the kettle or hot water heater the voltage is dawn down and the fridge won’t try to start. It seems to be working good as those other loads are only on for a short while and my fridge can return to normal working operation after a few minutes. I have a 2100 watt inverter and only a 200ah battery so the voltage can sag quickly with big loads. The LVD was inexpensive on Amazon. Who knows if it will last long.

Thanks for that info. I'll look at those. I'm looking at a 2800 to 3000w inv with 100+amp charger combo. The larger wattage is two fold, frugal, as it doesn't seem they cost that much more than a 2000w, and If I want to upgrade my battery bank and add another 110v appliance, I'm pretty well set.

Initially, I'm looking a two 6v in series at 230-250ah because my cook top and hot water are both propane. I'll also have an inverter generator if needed.

[kidharris]

Originally Posted by Simplicity

Thanks for all the replies.

1) I looked up inverter compressor refrigerators. The ones I saw were all full sized and expensive. Do you have a lead on something around the 4.5 cuft size with an inverter compressor?

2) The electrical math and lingo, at least for me, is tied with my understanding of women. Lots of short circuits on both counts.

3) I've heard of three ways to come up with start-up / surge wattage.

a) Rated Load Amperage (RLA) x 1.5. This seems reasonable. My home fridge is 4.5a x 1.5 = 6.75a x 115v = 776.25w start-up/surge

b) LRA - Locked Rotor Amperage (found on the compressor lable) x voltage. A small fridge with a 350btu compressor will have an LRA of ~8a. So, around 900w start-up/surge.

LRA - Locked Rotor Amps: The max current you can expect if the rotor is locked up.

c) 8 - 10 times the rated wattage. Xantrex support used 10 in their example. Online I find a mini-fridges run between 85-100w, an average house fridge is ~150w running with 800-1200 start-up / surge. Yet, at 8 - 10 times it would be more like 1200 - 1500w.

So, between the three ways, we've got 776.25w, 900w and 800-1500w.

My friend is a refrigeration contractor. He says what you want to know is the LRA. Multiply that by the voltage and that tells you the maximum your compressor will pull if the rotor is stuck (i.e., lockup). Your actual start-up surge will likely be a bit lower.

If you calculate your inverter wattage based on LRA amperage, you should be fine with your start-up wattage.

Rucker said his mini-fridge was pulling 8a at start-up and dropped to 1.5a when running. This would be ~3.5x.

Cadillac said 3.5 - 4x cold, 10x hot environment temp.

Ironically, I was searching a bit more as I was writing this and this question/answer came up on E-Trailers website: https://www.etrailer.com/question-442653.html

Question:
Can someone look at the nameplate on the Everchill 4.5 cubic ft 120V fridge, part # 324-000109, model BC-128B and tell me the LRA locked rotor amps? Am looking to size an inverter for this. I think the average current draw is 0.8 amps 96 watts and 24 hr running average is ballpark 0.69 Kwhrs about 30 watts so avg running power is 30 to 96 watts but locked rotor amps help determine the inverter size required. Thanks.

Expert Reply:
The Everchill RV Mini Refrigerator part # 324-000109 will pull around 8-9 amps on startup (LRA) and then around 1 amp while running.

LOL! I wish I had found this a few days ago. Lots of thinking and calculating could have been saved.

SUMMARY:
I think all three get you in a start-up surge ballpark.

I think the 1.5x method is maybe a bit on the low side. The LRA seems to be right about there for average environmental temperatures and the 8-10x is more worst case high environmental temp situations.

I guess if you're choosing an inverter, the worst case scenario is the one on which to base that decision.

Hope this helps someone else. I'm done!

Due to my ignorance on inverters I think that I would use the LRA (when motors are involved) and size the inverter similar to wiring, circuit breakers, and panels... add up all of the different appliance maxes that could happen at the same time and use that wattage as my total load. Maybe you could use additional inverters for different, little used, appliances/circuits so that you didn't have to have such a big inverter running all the time draining the battery. Just turn on the inverter when you use or turn on the appliance.



As far as I know, things that can start under varying load (such as a/c, fridges, fans, compressors without unloader valves, conveyers, pumps, etc.) can have varying start up surges, depending on load which is why you want to use LRA. The fact that most of these types of equipment can start up automatically compounds the problem (another reason to consider multiple inverters for some circuits?)

[Doktari]

Originally Posted by Simplicity

Thanks for that info. I'll look at those. I'm looking at a 2800 to 3000w inv with 100+amp charger combo. The larger wattage is two fold, frugal, as it doesn't seem they cost that much more than a 2000w, and If I want to upgrade my battery bank and add another 110v appliance, I'm pretty well set.

Initially, I'm looking a two 6v in series at 230-250ah because my cook top and hot water are both propane. I'll also have an inverter generator if needed.

I usually use 3000 watt low frequency inverter/chargers but I had sold my Victron Multiplus 3000 watt inverters because they were early 2012 models not designed for lithium batteries. They had no remote on/off switch like the newer ones. Then I stumbled onto this 2100 watt inverter/charger at a price so cheap on eBay I couldn’t afford not to buy it. I enjoy trying different equipment as a hobby anyway. But this Sterling Power inverter isn’t designed fo Lithium batteries either lol. So I’ll have to hack the inverter/charger switch to make it work with my BMS. Or swap it out. Anyway, that’s getting off topic. My point is however that you might consider buying one with a remote switch so if you decide to convert to lithium it works seamlessly. I just picked up a Samlex 2200 watt inverter/charger that is designed for lithium. Not sure if it works yet. I hope so as the specs sound very good.
Also, some of the advanced charge controllers come with a programmable voltage sensitive auxiliary relay that can be used to turn things on or off depending on voltage. I’m looking forward to trying those options someday. My friend uses his auxiliary relay to turn on or off a heat pump and other stuff. I think there’s a aux relay in the newer Victron 712 battery meter. Not sure about the new Victron smart shunt.
You mentioned a generator. One feature I liked about my old Multiplus was the Powerassist mode. The start up surge in my little air compressor was large the Honda eu2000i struggled to start it. But if I plugged the Multiplus into the generator and the air compressor into the inverter it started easily. I framed a shed using a nail gun. Point is I didn’t know I was going to be building a shed and was glad I had a 3000 watt inverter with Powerassist and the generator. I also didn’t know I was switching to lithium last year either.

[kazetsukai]

Originally Posted by Simplicity

Kaz - I'm doing a simple 30amp / 120v into an inverter/charger to as few batteries as I can to run the components I've listed. If I'm understanding what your edit comments were about only apply if I was doing split or 240. So, all I'd need is the Victron inv/chrg you suggested. Am I interpreting all that correctly?

Yeah that's correct.