Off-Grid Inverter Driven Fridge Starting Problem

Does the fridge start when every other load is switched off, perchance?

sounds like low voltage, is there a battery bank or are you coming straight from the panels?

It does sound like low voltage. I was driving the fridge (attempting to run it) as the only load from a 1.5kW inverter connected to a 70A/h car battery. I then tried it with an 80A/h car battery - same result. I then tried it with the inverter connected to the car battery with engine running - I thought that the alternator should be pretty low impedance.
What I could do is to scope the battery voltage and the inverter ouput as it cycles. Come to think of it I could also scope the pd across one of the leads supplying the inverter for an idea of the load current. Hmmm. I'll do that today (hopefully - bit busy at the moment) and post the traces.
Oh, don't worry about the scope, it has fully floating inputs - and its battery powered.

It sounds like your inverter can't supply enough current to start the fridge compressor motor. You either need a bigger inverter or a smaller fridge.

"Modified sine inverters are not all the same, and neither are the consumer gadgets we connect to them. Trouble comes when the upper and lower half cycles of the inverter's output are not identical. Similar if the gadgets we connect to it do not load the two half cycles in a balanced way - such as half wave rectifiers as found in some chargers.

A fridge compressor motor (or any inductive load for that matter) should be powered by a properly balanced supply. If the upper and lower half cycles are not in balance, it causes a significant DC current component in the motor windings, and this can spell trouble for both the inverter and the motor.
I think it is safe to say that pure sine inverters generally fit the bill better. Some modified sine inverters (with balanced output waveforms) are also able to get the job done, provided it is capable of handling the start-up requirements of the fridge. Problem is we do not know which ones are up to the job, and the school fees tend to be rather tough."

http://www.4x4community.co.za/forum/showthread.php/134410-Inverter-too-small?p=2017322#post2017322

It could be the inverter is not up to the job due to unbalanced waveform and/or inadequate output...I would check what your waveform looks like, and perhaps just go with a sine wave inverter...

http://www.campingworld.com/shopping/item/nature-power-sine-wave-inverters-1000-watt/67191

Why go for invertor at all ? Why not run the appliance on DC alone ? There will be no problem of poor sinecurve, square sine curve at al. I think, for stand-alone applications (Off grid) nothing is better than DC. Each day, I hear of some new type of battery or energy storage being developed, that has a long cycle life or more efficient storage, like the one in Nevada perhaps, where they use the solar power to drive some cable cars up a slope, and re-produce electricity by slow motion of them down.

It really depends upon the circuitry in the inverter. Most inexpensive consumer units do very poorly starting a compressor motor because it represents a highly inductive load with a high starting torque. Feeding a square wave to an inductor results in very large current spikes and the inverter stops.

A commercial inverter specifically rated for motor duty uses control circuitry that creates a stepped or modified sinewave independent of the load and can accommodate a low power factor starting load. You might be able to "fool" your unit by preloading it with a resistive load so that it's already "inverting" and the motor is just an incremental load to it, might take some experimenting with the exact size of the resistive load though.

or he could just toss the junk and spend money wisely the 1st time

when you finish with your scoping and searching for phantom DC, get an AC voltmeter and hook it directly to the normal running setup...same inverter, same load, get a voltage reading the entire time its attempting to start/ your readings will tell you plenty.

BTW..off grid to you means starting a petrol car for power????

The inverter in my

starts my humungous side-by-side Whirlpool fridge just fine. Even when the gas furnace is running and some lights and TV. And that is a 2000 watt sine-wave inverter. That little Honda is rated for 1600 watts continuous and 2000 watts peak (or starting) loads.

I'd buy a better inverter. This is what is in my RV. It is a Xantrex ProSine 2.0. Works great. Runs a 1,200 watt microwave just fine.

You're also going to need a better battery. My recommendation would be a 12 volt bank of GC2's. Preferably four of them, parallel/series combination. Even better would be to upgrade your electronics to 24 VDC. Keeps the copper requirements down. You can readily buy 24 V inverters as well. I use LED lights in my RV that will accept 9 VDC to 30 VDC because they have swithcing regulators to make constant current.

Good luck with your quest.

Don't use the cheap square wave inverters, pure sine wave inverters all the way when it comes to fridges or anything with sensitive or highly inductive or capacitive circuits. They don't like it and I have even destroyed a square wave inverter trying to power them.

If the size of the fridge was the main issue and you have ready access to propane or natural gas, this will get you 18 cubic feet (500 litres). The one in my RV also has an ice maker too.

By Norcold ~ $2,800 USD

I have not seen any mention of the wire size from the battery to the inverter. The locked rotor amps needed to start the compressor are reflected to the input (assuming 12VDC to 220VAC) by a factor of ~18.3. Are you sure your not starving the input to the inverter by a very large IR drop of the input wiring? Your 90W power at 220VAC is 0.41amps. Assuming 7X for lock rotor, 2.86amp surge at inverter output (this is 630watt output). But the input current at 12VDC is 52.5amps. How big is the wiring and terminal lugs sourcing this from a battery? You need to measure how much the battery voltage sags, but also the IR drop from the battery to the inverter on both positive and negative connections (this doubles your voltage droop). A cheep inverter is not going to provide the surge current at reduced input voltage. You should be sizing the input wiring to limit the voltage drop to less then 2% (a figure of merit that seem correct with 12VDC input). This is 240millivolts of 12V input. And each wire is half this at 120MV IR drop. Depending on the length of the inverter input wiring, you may need #4AWG copper or larger. Look at the battery termination, is this using a screw terminal post or the large clamped lead post? I understand you'll need to translate AWG to mm wire size, the point being to look at the input wiring.

The fridge probably has a capacitor start motor which becomes a total mess when run from a non-pure Sine wave inverter. Rather than the Cap providing a phase shift to start the motor the high frequency PWM waveform causes no useful phase shift at all.

You need a pure Sine wave inverter with a filtered output to use capacitor start motors. Alternatively you could fiddle around with some kind of inductive filter on the inverter output to try to get a pure low frequency waveform out of it...

Nolfese; I think that Sir Robin and Ignator are more on track here then anything else mentioned here. 70 AH battery is not enough to start and run the fridge you have. As well as the wiring may not be large enough to keep the voltage and current where it needs to be. I use 3000/6000 watt inverters with 285 AH battery in my commercial trucks to run all of my key machines, grinders, some lighting,and battery tool chargers for my hand tools. Now granted all of my inverters currently are modified sine-wave from harbor freight and they work well for what I use them for, but there are some things that they will not start like my 3 hp air compressor or my small refrigerator. Our camper on the other hand has a pure sine-wave Tripplight that will. It uses 4-6vdc 115 AH batteries, series and parralled to 12V-230 AH with which we have had no problems since 1971 except battery replacement every 4-5 years with minor maintainence on the batteries such as keeping the water levels up and bimonthly float charges to keep the plates clean of sulfation. And check the electrolyte levels to make sure the acid levels are up and not watered down by too hard charging with off gassing, with water replacement you can off set electrolyte levels and have too much water and not enough acid to drive you insane trying to figure why you can't run what you know you should be able to start and run. And now on to the wiring/cableing, my inverters are only 3ft from my batteries the power cables are 2-00 gauge cables nothing less or they heat up and lose amperage and voltage. and you need to clean all of your connections frequently and check for corrosion at all connections. just remember one thing when in doubt about wire size go bigger it wont fail you when using DC current for power. I think that about covers it. Duke,

Possibilities are as have been noted.

1. Wire size to inverter too small/ 12v circuit run too long. Keep the inverter near the battery.

2. An 86 litre fridge should run comfortably off a 600w inverter, but it needs to be pure sine wave, modified is not good enough. I use Giandels from Ebay, they're cheap, efficient and actually do output a pure sine wave under load. My 2800w one will readily supply up to 4000 watts for a few minutes without a problem and will run the RV airconditioner and the microwave simultaneously. Here in Australia, it is becoming normal practice to install domestic fridges in RVs, running 300 litre ones from 600w inverters and LFP batteries.

3. Battery too small. Upgrade to LFP batteries (these are very safe, unlike the LiCo ones that have a rep for letting the smoke out) and enjoy the benefits of longer life (around 4 times as long - sure they're dearer, but dollars per cycle are much lower), fast charging (will take everything your charger can deliver right up to 100% - unlike Lead acids which taper off to almost nothing at around 80% and waste much of your charger's ability), minimal voltage sag under heavy load (maintains better than 12.5v until almost flat - a LA will be down to 10.5v in less time). You can discharge them to lower than 80% DoD, and not getting them back to full charge is not detrimental as it is for LAs.

Spades; LFP not aware with that designation I know Lithium Cobalt just not LFP (Lithium Iron Polymer)?

Not a Lithium Polymer as such.

LFP =LiFePo4 = Lithium Iron Phosphate, also a close cousin LYP = LiFeYPo4 = Lithium Iron Yttrium Phosphate.

Lower specific energy density than LiCoO2 (LCO) Lithium Cobalt but far safer approaching full charge levels, almost impossible to make combust either spontaneously or by various methods of mechanical or electrical destruction.

There are numerous spin offs of the Lithium ion chemistry that are suited to specific purposes, and totally unsuited to others.

A taste of what's available, although not an exhaustive list.

1. Lithium ion - Li ion - the original chemistry and now a generic name for all of the Lithium species.

2. Lithium ion Polymer - LiPo - slightly higher energy density in a smaller package.

3. Lithium Cobalt Oxide - LiCoO2 - LCO - 3.6v/cell - high specific energy density but lower specific power, suffers easily from thermal runaway at high charge rates or heavy loading, short cycle life.

4. Lithium Manganese Oxide - LiMn2O4 - LMO - 3.7v/cell - higher rate charge and discharge capability but lower specific power than LCO. Safer than LCO but can also suffer thermal runaway if over charged.

5. Lithium Nickel Manganese Cobalt Oxide - LiNiMnCoO2 - NMC - 3.6v/cell - Popular for power tools etc. due to its high current capability in a small package. Cheaper to manufacture due to lower Cobalt content, but still suffers the dreaded thermal runaway if over stressed.

6. Lithium Iron Phosphate - LiFePo4 - LFP - 3.2v/cell - A low stress chemistry even at high charge and discharge rates, not likely to suffer thermal runaway even if overcharged. The cell of choice for recreational vehicles and starter batteries. Lower cell voltage equates to a lower energy and power than other chemistries, but the safety factor is a huge plus. Longer cycle life than other types - typically 4 - 10 times the life of lead acid, and 3 times the energy density for around a third of the weight and half the size for the same Wh capacity with a very flat discharge curve throughout its usable range .

All of these Li chemistries require adequate balancing techniques due to their inability to self balance when in series formation. A typical 12v 6 cell lead acid battery, when approaching full charge, may have one or more cells at different voltage levels, but the higher cells will simply gas and give off their excess energy as heat until such time as the battery terminal voltage reaches the cut off point, and so is in effect self balancing. Lis cannot do this, and so the higher cells can be destroyed if allowed to climb too high.

It is normal to have a voltage controlled discharge circuit across each cell which dissipates some of that excess voltage. These systems are prone to mishap if the charge rate exceeds the discharge ability of the bypass.

My own design circuit for my LFPs shuts off the entire charge circuit if a cell attains 3.65v, discharges that cell down to 3.55v and then restarts the charge. The next high cell will repeat the process until all cells are in relative balance. The circuit also incorporates a low voltage fail-safe in case the discharge circuit remains on, and also low voltage disconnect of the load circuitry if a cell approaches a too low voltage which can also be detrimental to the cell.

Hope this helps.

Would these cells be good for EV usage at 244 volts. What AH per cells and what type of cell construction pouch or Prismatic cells. Just thinking out loud here, wondering if I am out of the loop on new types of cells. Most of the cells sold here are LiPo very few other chemistries are available to us in the states because of import duties and taxes on top of that. You have an advantage of being near to manufacturing sites in Asia. I have a friend that imports products from Asia and we are trying to work a deal when he has a partial filled container coming over to fill the extra space with a set of batteries for my next project. A 60 Ford Falcon originaly a 6 cylinder 4 speed reimported from Europe when it did not sell there. Pretty bad shape when I got it just finishing rounding up parts to build. Have a Nissan forklift motor planning on installing in the rear with independent rearend out of a mustang bolted with a coupler direct to drive flange of rearend. Which is why I am courious about these chemistries you have mentioned here.

LFP cells are regularly used for EVs here, mostly due to their cycle life, high charge and discharge rates, safety characteristics and power density - the rate at which power can be drawn from them.

For instance - a LCO cell has a maximum discharge rate of only 1C, a LMO cell can go as high as 10C in some cases, and LFPs can be 15C or more.

Prismatics are the most popular version, with Winston brand being possibly the most popular of them.

The last lot of prismatics that I purchased cost me AUD1.74 per Ah per cell, ie a 12v 600 Ah set made up of 8 x 300Ah cells cost me $4176.

I expect that pouch cells would be comparable, they are mainly used in prepackaged battery sets here.

The prismatics are now in my RV, and are roughly equivalent to 950Ah of lead acids. They weigh 83Kg as compared to the LAs being around 300Kg, and they occupy about half the space.

I face the same dilemma, whenever I want you use 12 V DC for any appliance. A pedestal fan consuming 22W, any number of LED lights can work, but when it comes to a motor, the current is very high. For example for a 1 HP motor, about 750 watts, the amperage shows a whopping 72.5 amps, and the conductors have to be atleast 5 sq.mm copper. Perhaps, increasing the voltage (Of course DC) to say 110 volts, will bring down the amperage in the circuit. DC/DC converter, of course all electronic, are available, and not very costly too.