Refrigerator start surge

Joe94Joe94 Solar Expert Posts: 42
I know I've read what I'm looking for somewhere in this forum before but I can't find it. I have a small chest freezer I converted to a chest fridge. I've been using it at home and have it down to about a 175wh a day. I tested the inrush current with my fluke and it showed 6.7amp. I want to take it out to my off grid place but I just have a suresine inverter. I think it was Wayne that modified a few of them to work with his suresine but I can remember exactly what was involved. I obviously will need a start capacitor. My plan was to get a Supco RC0410 and see if that softens the start surge enough. If I recall there was a bit more to it then simply adding a start cap though. I figured i would see if someone had a working recipe that would save me some time and experimenting.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,858 admin
    Re: Refridgerator start surge

    Wayne explained it (at least an overview) in this thread:

    600w Inverter won't run 1.2a chest freeze?


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Refridgerator start surge

    Oh My! I hope you're ready for this! lol
    After explaining it a few times I made it easy on myself - - saved it so all I had to do now was copy and paste. :D
    "Converting a freezer to fridge
    Each of the half doz I've modified was done slightly differently. First off, you have to have a good understanding and ability with electrical etc. I'm not aware of anyone else having done this, but obviously it can be done.
    First off, the original equipment varistor starter must be removed and replaced with a relay controlled by a timer of some sort, to apply power to the start winding for a short time. This time has been different for each unit I've modified. The first ones were timed by a simple resistor/capacitor delaying the action of the relay. The last one uses a 555 timer IC and that works much better as a timer. Second, a start capacitor must be wired in series with the start winding. The value of that capacitor is VERY critical. Too big and the inverter is overloaded and shuts down, too small a value and the motor won't start. Each of the ones I did required a different value capacitor, as each motor was different. The values ranged from I think 200 MFD (was a few years ago), a;; the way down to 66 MFD if I remember right. I'm lucky I have a friend operating a motor repair business, and he loans me several different values, allowing me to try each to see which one works best. If the units were operating on grid, or a bigger inverter, the cap size wouldn't be so critical, but the TS-300 is being pushed to it's very limit with every start, resulting in a VERY fine line between getting the compressor up and running, and shutting down on overload.
    But you're not done yet! Each and every unit I've done, normally draws so much current on startup, even with these modifications, that the inverter shuts down before the compressor gets up to speed. The next step just barely takes care of that. You must use a transformer of some sort, I use autotransformers, rated for roughly 100 VA, that will drop the voltage from the inverter by roughly 10%, and in doing so, increase the available current to the motor by that same rough 10%. This is just enough, with all the other modifications, to get the motor up to speed, but as soon as it is up to speed, the starter relay must be timed exactly to kick out the start winding, and at the same time, switch over a DPDT relay which takes the transformer out of the circuit, and connect the now running motor, directly to the TS-300. It's not going to be easy, will take some frigging around and trial and error to get it working right, but it can be done, as I've said, I've already done it at east 6 times.
    Of course it goes without saying, that all these mods will void your warranty , and of course the CSA or UL approval. Hahaha
    But for me, it's perfect. Have had two freezers and a converted fridge running with these mods, all on TS-300 for 5 years now. No, they don't all run at once! The fridge had priority, so when it wants to run, it powers a relay that disconnects the other two units. When it's not running, the freezer in the basement is next, then finally, if neither of the first two are running, the freezer in the outside shop has it's chance. The "fridge" only runs an average of 5 minutes per hour, so there's lots of time for the other two.
    So there you go. That's the best I can describe it. Like I said, you'll have to be proficient in electrical and have access to all the things you need.
    To be perfectly honest, it would be a whole lot easier for you to just use a larger inverter, capable of starting and of course running your fridge, and have the thermostat control the on/off of the inverter so it's not running when it's not needed."
    To be perfectly honest, it's far easier to get a bigger inverter than to struggle with all the above.
    Wayne
  • Joe94Joe94 Solar Expert Posts: 42
    Re: Refridgerator start surge

    Thanks Bill and Wayne. That should give me plenty of information to get this thing working. I agree that getting a bigger inverter is the right way to go. I'm planning to add a second larger inverter down the road. I do like having projects to keep me occupied though. I forgot about the transformer I'll have track something down. My plan was that if the Capacitor didn't bring the current draw under 5amps then I was going to use a thermistor to increase resistance as the draw gets up to 5amps and see if I can get it going without faulting the inverter.
  • westyd1982westyd1982 Solar Expert Posts: 85 ✭✭
    Re: Refrigerator start surge
    Joe94 wrote: »
    My plan was to get a Supco RC0410 and see if that softens the start surge enough.

    I've tried both the Supco URC0810 and the URC0410 on my small chest freezer and neither lowers the start surge enough. Both do lower the power draw by 3-5 watts when the freezer is running though - I think because it replaces the varistor starter with an electronic unit.
  • jonrjonr Solar Expert Posts: 1,350 ✭✭✭✭
    Re: Refridgerator start surge

    Has anyone done much with adding additional parallel capacitance (similar to a run capacitor)? Ie, try to fix the poor power factor while the motor is starting? Maybe switch it out once the motor is running so as not to over-correct.

    I agree that there are three stages to a motor start:

    The initial inrush of current for ~1 cycle. This is caused by inductance and capacitance and changes depending on exactly where in the cycle the switch turned on.
    The period while the motor is coming up to speed. Extra current is needed to start the motor. PF is poor. Small voltage reduction can help.
    Normal run. Low amps, needs full voltage, hopefully PF is close to 1.0.

    It seems to me that a device that switched in different resistors in stages 1 and 2 might be helpful. Or perhaps something similar using a mosfet/PWM ramping up or an inrush thermistor.

    I am available for custom hardware/firmware development

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Refridgerator start surge

    Power Factor is only one aspect of refrigerator draw problems. The fact you're trying wind up a motor to 1750 RPM from a standstill against a head of compressed refrigerant is another.

    Start windings don't actually suffer from PF so much because there is a start cap involved and they are only active for a short time (little reactive resistance change). Beyond that the run cap on those windings has only so much effect in reducing the initial demand.

    You can't keep correcting PF until it goes away and the motor magically starts and runs on 1/10th the power it originally did. Yes, really good motors have both start and run capacitors and yes it helps a lot. I just put in a well pump here that has both and the start is 6 Amps and the run is 3 Amps (240 VAC). But it is actually easier to start a submerged pump at the bottom of a 90' well against 30 psi of water than to crank over a 'frige compressor.

    It's just plain hard to get these things started. You can improve it over what the maker did (they don't care because most people have 1.8kW of power available) but there is a point where further improvement involves things like Wayne's clever resistive current reduction or VFD devices etc.

    Compared to sorting that (and don't count on every motor being the same 'cause they're not) simply getting an inverter capable of handling the surge demand is much more practical.
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    Re: Refrigerator start surge

    Because I have a 1600w inverter that is already powering a few other things, to solve the few seconds of the fridge starting up, was to get a 2nd hand online (not offline or inline), a online UPS to handle the surge.

    It was a lot cheaper than getting a bigger inverter.

    When the fridge fails one day, I will get the proper A++ rating.

    I figured that to replace a good working fridge and someone else throws away a working online UPS (that just needed 4 x 9ah batteries), was not the green thing to do.
  • jonrjonr Solar Expert Posts: 1,350 ✭✭✭✭
    Re: Refrigerator start surge

    My rough guess as to start current reduction is:

    lower voltage - 15-20%
    autotransformer - another 15%
    PF correction - 75%

    I am available for custom hardware/firmware development

  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Refrigerator start surge
    Because I have a 1600w inverter that is already powering a few other things, to solve the few seconds of the fridge starting up, was to get a 2nd hand online (not offline or inline), a online UPS to handle the surge.

    Well remember, cheap inverters that CLAIM to be 1600 assume a PF of 1, and some have crazy stupid short "surge" times (like 500ms) which wouldn't be enough to start anything anyways. My neighbor had a "claimed" 2500/5000 inverter, some cheap one, and THAT would not start his fridge at all. Yet a high quality 1500 started it fine. Just some thoughts.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.BB. Super Moderators, Administrators Posts: 29,858 admin
    Re: Refrigerator start surge

    Pretty much what you typed... Add that poorly wired/connected DC wiring/failing battery bank can hurt too. Even a good quality Inverter on a 12 volt battery bank with "jumper clips" will hardly start up and run a small load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    Re: Refrigerator start surge
    jcheil wrote: »
    Well remember, cheap inverters that CLAIM to be 1600 assume a PF of 1, and some have crazy stupid short "surge" times (like 500ms) which wouldn't be enough to start anything anyways. My neighbor had a "claimed" 2500/5000 inverter, some cheap one, and THAT would not start his fridge at all. Yet a high quality 1500 started it fine. Just some thoughts.

    That is so absolutely true. Been there, done that. Today I trust Victron having tried 2 other makes before.

    Locally the solar sales people always recommend a bigger inverter when a fridge is mentioned. Also mentioned is the replacement of said fridge for a A++ model.

    But here is the thing. If you have a good make inverter, your load is well within the 80% capacity of the inverter, the array and batteries matched to the inverter, and you get the bright idea to add say a existing fridge, with resultant continuous power usage still well within 80% ballpark of the inverter with the only problem the start-up of the fridge, the most costs effective tried and tested solution till you can replace the fridge, is a 2nd hand online UPS.

    It is by far the safer option compared to add parts and / or accidently getting the wrong parts / or installing them wrong thereby damaging the fridge, to handle the spike if you are not technically minded.

    No solar sales person I have spoken to, to date, has ever even considered this as a temporary solution. As a matter of fact, most of the local guys do not like it at all for it robs them of a sale.

    The UPS industry has been around for a long time. UPS's are tried and tested, as safe as can be with the added benefit of ensuring the safety of your equipment. A on-line UPS's, if you are in a corner, is a very cost effective solution, with added protection your equipment.
  • jonrjonr Solar Expert Posts: 1,350 ✭✭✭✭
    Re: Refrigerator start surge

    Expect single phase motor (and transformer) starting currents to go even higher - it's a side effect of greater efficiency. Permanent magnet/inverter driven motors are a good solution.

    An online UPS running off of another inverter means that you double the losses. Running it directly from existing batteries is fine, but it's the same thing as adding another, bigger inverter.

    Looks like the ICM803 hard start device works by adding PF correcting capacitance during start and then switches it out. Certainly an easy device to add.

    I am available for custom hardware/firmware development

  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    Re: Refrigerator start surge
    jonr wrote: »
    An online UPS running off of another inverter means that you double the losses. Running it directly from existing batteries is fine, but it's the same thing as adding another, bigger inverter.

    Yes to both.

    As I said it is a temp solution till you can upgrade after maybe selling the smaller inverter. :-)

    Or use the UPS for the fridge until you can upgrade the fridge to fall within the existing inverters ability, then remove the UPS. Add another panel to cover the additional load of the UPS if you don't have spare capacity already, for you will use that panel's power inevitably. :-)

    I just found that with us newbies starting off, with all the help / yet limited cash / no experience / no electrical background / too much info at once / inevitably having purchased the lower spec parts, not forgetting the inevitable mixing and matching we are going to do as we learn more, is that we learn a whole lot more of the actual usage / practical side if we have a bit more space to safely play in at no little to no extra cost so that we can eventually specs the final system to the T, thanks to all the help here.

    A online UPS gives one that experimental chance at less of a cost than a new inverter after just having purchase the 'wrong' one.

    Even more so if you can get that UPS 2nd hand or for free because someone chucked it due to it not 'working' anymore due to old batteries. :-)
Sign In or Register to comment.