VFD to up from 50 to 60Hz 3

[Grizlyadams]

Hello,

while searching the interwebs for info, I came across this thread thread248-395067 which lead me to post this.

My situation is that I have an American RV in Europe which has been partly converted to 230v. The roof air conditioners and the water heater remain as 120v and are powered by a 230 to 120 converter when the RV is plugged into mains power (220-240v). When not plugged in the 230v side of the RV is powered by solar/batteries/inverter and the 110v circuits are not powered. It has an onboard 5.5kVA 120v/60hz generator which can be used to power the aircons and charge the batteries when necessary.

The aircon units are rated at 115v 60hz so, my understanding is that when the aircons are running on 120v 50hz they are "underperforming" by about 17% (50 is 83.33% of 60)?

So, I have a few questions:-


1.

is there such a thing as a simple frequency regulator, like a volage regulator without the need for a full on VFD​

2.

if the answer to 1. is no, can I use a single phase to single phase VFD and up the frequency to 60hz to get back to 100% power on the aircons?​

3.

What would then happen to the VFD when I run the generator - would it simply take the increased frequency and still output 60hz to the aircons?​

4.

The aircon motors both have a minimum breaker spec of 20 amps - they don't draw that as I can run both of them on a 10amp mains connection. They have an RLA of 11.3 and 6.7 amps front and rear respectively (18amps) so does that put simply means that combined they draw 9 amps on 230v ? or is that an over simplification? Neither of them have soft-starts on but they do have compressor delays so on initial start the fans will run, then the compressors kick in after a short delay)

5.

if there isn't such a thing as a frequency regulator - can I use one VFD for both aircon units? (each aircon unit has two motors - the fan/blower and the refrigerant compressor​

links to any suitable devices/documentation would be gratefully accepted and much appreciated.

thanks in advance.

​

 

[waross]

Just run your generator.
The cost of other options will pay for a lot of fuel.
Or replace your A/C with 50 Hz A/C.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Heaviside1925]

OP,
I agree with waross
Consider three things - cost, complexity and efficiency
Can I increase the efficiency of my $500 air conditioner to 100%? yes, using $2000 worth of equipment.
Can I add multiple different voltages and conversion devices throughout my RV? yes, but you will need to maintain all of them and likely pull your hair out troubleshooting them later.
Can I increase the efficiency of my air conditioner to 100%? yes, by adding conversion devices that have their own efficiencies and losses.

I am not sure of your technical aptitude but there could/maybe a simpler path forward. It will depend on the age/make of your RV and air conditioner unit. RV air conditioner makers, make air conditioner for all sorts of RV manufactures, so some of them make the air conditioner itself a universal design and either have a control board that accepts multiple voltages or individual control boards for each voltage, so the air conditioner manufacture needs only to either change the wiring or the control board depending on the requirements of the RV manufacture. You'd need the tech manual and / or schematics for your specific unit but if it is set up this way, it could be a matter or just switching some wiring or buying a new control board.

 

[jraef]

Do frequency changers exist? Yes.
[ol A]
[li]Are they “simple”? Could be.[/li]
[li]Are they affordable? Could be (although that’s subjective).[/li]
[li]Are they reliable? Could be.[/li]
[/ol]
Of the list above, pick two…


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

If your A/C is driven by a conventional induction motor, changing connections won't help.
If your A/C is one of the newer designs, with the motor driven by either a VFD or a linear compressor motor, you may be able tochange some settings, or it may just adapt automatically.
Given the poor quality and emphasis on cheap by the RV industry, you probably have a Plain Jane simple induction motor driven compressor, so disregard most of this post.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Grizlyadams]

Thanks for your replies.

Following on from my original post, I see you can indeed get frequency regulators, but they appear to be large, industrial and very costly. So back to my original questions 2, 3, 4 and 5

2. can I use a single phase to single phase VFD and up the frequency to 60hz to get back to 100% power on the aircons? (everything I see seems to convert single to 3 phase - I installed one of them to run my tyre changing machine in my single phase workshop)

3. What would then happen to the VFD when I run the generator - would it simply take the increased frequency and still output 60hz to the aircons?

4. The aircon motors both have a minimum breaker spec of 20 amps - they don't draw that as I can run both of them on a 10amp mains connection. They have an RLA of 11.3 and 6.7 amps front and rear respectively (18amps) so does that put simply means that combined they draw 9 amps on 230v ? or is that an over simplification? Neither of them have soft-starts on but they do have compressor delays so on initial start the fans will run, then the compressors kick in after a short delay)

5. can I use one VFD for both aircon units? (each aircon unit has two motors - the fan/blower and the refrigerant compressor.


@waross - pretty sure my neighbours wouldn't be overly enamoured with that and leccy is free and petrol is $7.20 a US gallon here.

@Heaviside1925 -

I wish they were $500 - closer to £1600 + each and then they are not plenum type, they'd need significant modding to work on the RV.

Of your cost complexity and efficiency only cost is key, I don't really care about efficiency if I can get the aircons outputting to their design spec. - power is free. I'd be more than happy to remove the current 22 to 110 transformer and replace it with something that stepped down the voltage and stepped up the frequency for the whole 110 circuit - but I guess if it was that simple, it would have been done by now, although the 220v conversion was done 16 years ago.

Unfortunately these aircons are very American and thus have never had 220v/50Hz option as they were never made for any market other than NA RV market.​

@waross -

yes - they are both old and simple - my RV is a 2003 model and I reckon the aircons date back to mid/late 90s design wise - they are Coleman Mach 3 Plus and Mach 1, neither of which are made any longer​

thanks again.

 

[Heaviside1925]

OP,
Have you considered upgrading your low voltage system? Instead of going from 230 - 120VAC 50hz, go 230 to 24/12VDC then 24/12VDC to 110VAC 60hz. So, either your gen-set, shore power or solar could charge your batteries, and supply your 110VAC 60hz from there.

Side note: I looked up the Coleman products you mentioned and they sadly seem to be for 120VAC only. I only ask because a couple weeks ago I helped a friend trouble shoot a 30-year-old marine refrigerator/freezer unit that had a control board set up for multiple voltages, so I was hoping there might be way but Coleman and

poor quality and emphasis on cheap by the RV industry

this seems to not be an option.

 

[Grizlyadams]

Just thinking about it further and not sure why I didn't think of it earlier - I think the answer would be to install a second, 12v-120v (pure sine), inverter alongside the Victron 12v-220v inverter that I installed for the lithium/solar system.

I could then ditch the 220v to 120v transformer and the 110/120 circuits would all be back to 60hz...

 

[waross]

Compressor replacement is a common event for A/C repairmen.
Check with a local HVAC shop on the cost of replacing your present compressor with a 50 Hz compressor.
Option #2;
A VFD is a special type of inverter.
Look for a single phase inverter (NOT VFD) with enough surge capacity to start your motors.
Then buy or build a battery charger or DC power supply with enough capacity to supply the DC to the inverter.
Hint:
Look at the Solar market.
Some of the earlier solar inverters included a battery charger.
I am not sure if the chargers would support full inverter capacity.
The hours to Google that are yours. grin

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

You beat me by six minutes,

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Grizlyadams]

thanks again both!

I appear to have been writing my inverter post at the same time as you @Heaviside1925! That appears the best way - now to find an economical inverter! I suppose the Victron route is best as that's what I installed for the 220v side, and it will integrate with the Victron monitoring systems too - my issue there is the size of the unit and the (lack of) space I have left in the locker I installed it all in doesn't leave me enough room for another one the same size - I'll check if they do a physically smaller one but it does need to be pretty beefy to run the aircons at their rated RLA of 18amps combined so it'll need to have a surge rating of over 7kw (unless i fit soft-starts) and a constant rating of 2.5 kw (they draw 2070).

I guess the marine market may be different - I used to own a Cruisers Yachts (American made) 30ft boat and everything in that was 220 or 110 and it was only slighty younger than my RV ('06).

@waross - when I get back to the UK I'll ask the guys who re-gasses/services them about compressors, but there are also the two fan motors that will need doing - I guess they may be pretty simple as they're just 1/3rd HP motors, nothing special so I should be able to find matching size ones. I am veering towards the second inverter now though as that will mean I can run the aircons from the batteries/solar and won't need to run the gennie.

thanks again - just talking stuff thru lifts the brainfog!

all the best.

 

[Grizlyadams]

of course when this hot weather passes, the problem with go away!

 

[Heaviside1925]

OP,
No problem and glad you are out of the brainfog! I will say that unless you truly have need of 220 in your RV outside of maybe a few appliances, consider getting rid of the 12vdc -220 inverter all together and going full "yank" with just 110. I understand you may have a "brit" tv you'd like to plug in, but Labor Day sales will be starting soon at walmart.com and I'm sure you could pick one up for a song.

 

[waross]

Given the fan curves, You may be able to use the fans as is.
And a slower fan means a little more air but cooler air.
If you are able to power or exchange the compressor, you may not need to change the fans motors.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Grizlyadams]

@Heaviside1925 - full 110v really isn't an option really - everything in here is now 220 (or using boost converters to run off 12v. I've ditched the US microwave and the evap. fridge - both just crapped out. I now have a domestic fridge that cost me a little over £200 (I bought two because that's easier than re-jigging the hole to fit another! Same goes for the washing machine I retro-fitted (it didn't have one when I bought the RV).

My fridge failed earlier this year whilst in Portugal, I just found one at a local retailer for €200 that fitted the hole, not correctly but well enough while I had the other one repaired - repair was €70 - if I hadn't been about to depart on a trip I wouldn't have worried with the temporary replacement. That just wouldn't have been an option if it was a 110 or the original (awful) evap. fridge (£2500 and impossible to source in mainland Europe - UK only. Mainland Europe does not do RVs - Sweden a few, but nowhere else). The main TV and surround sound AV Amp are 220, the coffee machine, new microwave, toaster, mincer food processor etc etc are all 220 and all replaceable at any European retailer, albeit with the wrong plug on for my UK sockets - but I have a stash of them to hand!

@waross - that'd mean running two circuits as the fans would still be 110v, no? I've just looked at pricing and a suitable Victron inverter with my dealer discount is less than £400, I already have the 12v cable from the original electrical install I did, so apart from a consumer unit, an rcd and a breaker plus some mains cable and perhaps another victron Lynx busbar, I think it's doable for under £500 - I'll probably just rob a bit of locker space from the locker next door to my "electrical" locker. That's a result really as it solves my issue of not being able to run the aircon(s) off battery too, which was on the never-decreasing list of THINGS TO DO.

 

[Heaviside1925]

OP,
Understood, it sounds like you are going down the best path and you will now have an international RV! Happy caravaning! (I think I am using that term correctly).

 

[Grizlyadams]

hah ha not quite; a more accurate term (for the UK) would be motorhoming - a caravan in the UK is what you guys call a travel trailer. "Motorhome" is the British word but we tend to differentiate American self powered motorhomes as "RVs". Autocaravanas in Spain and Portgual, Husbilar in Sweden (house car), Campingcar in France to name just a few!

 

[LittleInch]

Don't forget the 12V amps will be rather big. Running 2500W at 12V is 208 A. That's a pretty thick cable and switchgear.

My home Solar system and batteries run at 55V and that cable is a decent size for only 1800W.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Grizlyadams]

@LittleInch - yeah, thanks - I have that covered. The battery I made and installed for the solar/230V inverter is 560Ah and I used 120mm² cable to the bus bar and the same from the busbar to the 230V inverter/charger (slightly bigger than "0000") which is rated at 600A and the class T fuse I have on the positive from the battery to the main isolator switch before the busbar is 400A (might need to up that to 500A with both inverters installed) - each individual circuit off the busbar is also fused (and cabled with the cable rated higher than the fuse and load ) for the expected load +25% on that circuit.

In hindsight and if I did it again, I'd use 48V rather than 12v and use a DC to DC for the 12V systems in the RV as the cable routing was a difficult; I built a full, dimensionally accurate mock-up of the RV locker in my workshop (it's an odd shape with the door being smaller in height because of the slide-out above it) so I could experiment with different mounting positions taking ventilation spacing and cable routing into account - trying to keep the 120mm² cable runs short and not too tight in radius was a challenge for which the mock-up was extremely useful! Not to mention the cost saving in cable for 48V!

 

[waross]

Do you have a charger that will support that current draw?
Thinking outside the box;
How about a 60 Hz Uninterruptible Power supply large enough to support your A/C?
You may have to hack the control circuit depending on how it is set up.
The input rectifiers don't care if they see 50 Hz or 60 Hz.
You DO have to find one that has a full power charger, or add an external charger.
It looks good on paper, the challenge is finding existing hardware that matches the paper specs.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!