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.

​

 

[Grizlyadams]

@waross

>> Do you have a charger that will support that current draw?
the batteries are spec'ed at 0.5C (280A) ideal charge rate and 1.0C (560A) max charge rate. The Victron inverter charger I have will do a max of 120A charge assuming shore power and or gennie is sufficient (gennie is, sometimes shore power isn't. The 1Kw of solar will give anywhere between 750W and 1250W (around 50 to 60 amps)

So, assuming I'm using both the aircons when it's sunny and plugged in to shore power, I will have a deficit of 30 to 40A, and no deficit if I'm only running one of the aircons. IF I'm off grid I can run the rear aircon as that's "only" 750w

>> How about a 60 Hz Uninterruptible Power supply large enough to support your A/C?
only issue there is weight and space - I'd effectively be adding another massive battery, most likely WLA of some description (not sure if UPSs use LiFePO4 yet)

I've actually found a Victron inverter that will be perfect on eBay UK

 

[waross]

Running on the grid or on the gen-set, If your charger is able to support the draw of the output, you will be able to run indefinitely without discharging your batteries.
You don't need a UPS, you need a 60 Hz inverter and a 50 Hz to DC power supply to support the DC bus.
A UPS has the inverter and a charger, (and some circuitry to control the UPS function).
If the UPS uses a 12 Volt battery, just jumper it to your existing battery bank.
If the UPS uses a different voltage consider reconnecting a small number of your existing batteries.
I suggest that running the AC on batteries for any reasonable will not be feasible.
I suggest that when grid power is available, the UPS will be working on feed-through mode.
That is, 50 Hz in, rectified, and 60 Hz out, with the battery floating.
(Feed through versus by-pass. Bypass would bypass the inverter and output 50 Hz rather than 60 Hz.
You may have to cut an internal wire or trace to disable by-pass mode depending on the specific UPS model.
If the grid is not available, you may not be in a park and you may be able to use the Gen-set.

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

 

[Grizlyadams]

In Europe shore power is 230V 6A maybe 10A, sometimes 2A! There is slim chance that I can charge the batteries to support the aircons and the rest of the RV's power draw. And as I said, my current battery charger (the inverter/charger/) will only charge 120A max. Thus the UPS wont work on passthru, if it were only the aircons, maybe (with 10A shore power and no other draw/losses accounted for)

Yes, running both he aircons on the batteries only is not feasible really - the battery is a 6.75KWh and the two aircons draw 2100W, so 3 hours of aircon at best. The beauty is that I can choose which aircon to use and they'll be performing better on 120/60!

At the moment, I'm running the RV on solar/batteries during the day and dedicating all of the 10A shore power to the aircon(s).

Can't connect the UPS battery and the current battery as the UPS will be lead acid type (WLA, AGM or similar) and the battery I made is Lithium iron and would destroy the UPS battery in very short order.

The eBay inverter is promising (I'll get new if that doesn't materialise).

Now I need more batteries and especially more solar! Can never have enough of either! Running out of roof space though?

 

[FacEngrPE]

A VFD has the power electronic parts to be a frequency converter, but the programming of a VFD intended for motor control does not do constant voltage control needed for a branch circuit.

Searching for 220v 50hz to 110v 60hz converter, will find some devices that do the frequency conversion and some that do not. Here is a advertising discussion from an outfit that sells actual frequency converters.

Before purchasing one of these or something similar, investigate if it will start your motors. Some inverters will brickwall rather than attempting to supply starting current, resulting in a motor that takes excessively long time (if ever) to reach operating speed.

Brickwall - when used with inverters, is when current is available up to a set limit. If current demand is higher than the current limit, voltage collapses, but current is still supplied at the preset limit.

 

[waross]

2. Can I use a single-phase to single-phase VFD to increase the frequency to 60 Hz to get back to 100% power on the aircons?

I doubt that you will find one.
One parameter in the design of three phase induction motors is the Volts per Hertz ratio.
A VFD has no problem maintaining the correct V/Hz ratio for any speed.

Some additional parameters in many single phase motors are speed related and frequency related.
Speed related;
Centrifugal starting switches will not switch at lower speeds.

Yes, I know that this may not be an issue at 50 Hz, but most clients consider a VFD for motor operation over a greater speed range. Rather than be limited by the constraints on a single phase motor they willopt for a single phase to three phase VFD and use a three phase motor.​

Frequency related:
Another design parameter of single phase motors is the capacitive reactance of the any capacitors.
Capacitive reactance is frequency related.
Bottom line; There is almost a zero market for single phase VFDs and no-one builds equipment for such a small market.

Look for a suitable 60 Hz inverter.
OR.
If your A/C works at all on 50 Hz, use it as is and do your southern touring in the cooler months. Head north in summer.


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

 

[waross]

Another possible option:
Buy a suitable window type A/C and mount it on heavy duty drawer slides.
This may be cheaper and easier.

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

 

[Compositepro]

It is simpler than using drawer slides. A/C units are roof mounted on RV's and window can also be roof mounted with simple ducting, built like a box.

 

[LittleInch]

These guys?

https://www.ato.com/single-phase-vfd

But may not work...

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

 

[waross]

Nice find, LittleInch LPS
If you try this you will want to use as short a ramp-up time as possible.
You may want to start with zero ramp-up and let current limiting take over.
A small A/C typically starts with no differential pressure.
Trying to start a recently stopped A/C against residual head pressure will result in a stall.
You want to get it up to a speed where the flywheel effect becomes active.
While a long ramp-up time will keep the starting current low, it may allow the head pressure to build before the flywheel effect becomes active and result in a stall.
Despite that warning, LittleInch may have solved your problem.

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

 

[Grizlyadams]

Thanks all for the further replies/suggestions - as I mentioned early on in the discussion, I've got a Victron 12V/3000VA 120V which is rated at 2400W (3000VA) continuous and 6000W peak load. I've set it to 120V/60Hz - somewhat serendipitously one came up on eBay just when I started this thread and I won it at about 35% of new price, so that, the soft-starts and the cabling combined was less than £400 which is by far and away the least expensive solution for me.

I have a couple of soft starts to fit to the aircons just to help the start load, although they do both run with stops and starts on the 230V 10A supply they're on.

@Pandit1 - point 4. those are the calcs I used for assessing the actual amp draw on the aircons (both aircons combined, not each) I ignored the 220V to 120V transformer losses in my calcs. The 10A breaker (230V) does sometimes trip, but when I look at the data that my Victron kit logs it happens when the voltage drops below 208V which makes sense as the amp draw will increase enough to trip the breaker.

So based on that, they are drawing between 2100 and maybe 2200 watts (at 215 volts the breaker doesn't trip at 200-208V it does so, ballpark (not counting transformer losses) they're around 2100 maybe 2200W combined which is way less than their data plates state.

Haven't installed the inverter yet - waiting for some kit to arrive (cable etc) and will test/monitor before installing, but I'm pretty sure it will all be fine.

thanks again for all your input.