Vac-bagging problem - calling all Electrician's

Built myself a vac-bag rig, however on giving it a trial run a problem has come up that I need to fix before I can use it properly.

First some background on the way it's wired up:

- when I pulled the fridge motor out of the fridge body I had to cut a cable running out of the wiring box on the side of the motor and up into the fridge body itself, this cable ran up to the thermostat and light in the fridge, and it's to the wires in this cable that I hooked up the micro-switch which turns the motor on and off according to the vacuum pressure in the vac-bag.

- I downloaded the wiring circuit diagram from the manufacturer, and on checking this out, a neighbour who's an electrician figured out which of the four wires in the cable I should be connecting to the microswitch. The four wires are:

- a brown wire (marked "L" where it goes into the wiring box)

- a blue wire (marked "N" where it goes into the wiring box)

- a green and yellow wire (no marking for this one on the wiring box, but the wiring diagram indicates it's the "Earth" wire)

- a black wire (marked "C" where it goes into the wiring box). According to the circuit diagram this wire is hooked up to a "main" winding" and a "start winding" with a "start relay" linking these two windings together on the other side and continuing on out to the "N" terminal.

The wires that have been hooked up to the microswitch are the brown ("L") and black ("C") wires.

Ok, now here's the problem:

1) I turn the rig on at the powerpoint, the fridge motor turns on, sucks the air out of the vac-bag until it reaches the desired level of vacuum, at which point the micro-switch turns off the fridge motor. All good so far.

2) Naturally air leaks into the vac-bag, lowering the level of vacuum below that desired and the microswitch gets triggered again and supplies power to the fridge motor. Again, exactly as desired.

3) However, instead of the fridge motor turning on and sucking air out of the vac-bag, it sits there with a small humming noise coming from it.

4) If I turn off the power at the powerpoint and switch it on again the fridge just sits humming at me, but if I turn off the power, leave it for 5 minutes and turn the power on again the fridge motor fires straight up and we go through steps 1 to 3 (as listed above) all over again and I'm left with the vac-bag sitting humming at me again.

I'm wondering if there's some kind of a capacitor (the start relay perhaps?) in the fridge motor circuit that allows power to flow through the rest of the circuit when power is applied and it is not charged, but when power is applied and it already has a charge it allows no power to flow through the circuit (some kind of power-surge protector perhaps?).

If so, and this capacitor needs to be immediately discharged when the microswitch turns off the fridge motor, perhaps the green/yellow ("Earth" wire) should be connected to the remaining terminal on the microswitch so that the circuit gets "Earthed" and drained of power when the microswitch is "off".

I'm also wondering if the "N" wire should have been connected to the microswitch rather than the "L" wire as my neighbour mentioned that "L" stands for "live" or "active", and earthing something like this sounds kind of risky.

Regardless of what replies I get to this, I'm going to go ask my electrician neighbour to give me a hand fixing this problem as this is 240 volt power we're dealing with and there's no way I'm going to play with it.

However I would like to understand what the problem here is (my neighbour did me a big favour by giving me a hand with this the first time and I don't believe he'll be too happy at having to come over again, so I'd at least like to be able talk semi-intelligently about this thing).

Cheers

there should have been a capacitor in the old fridge that would have been connected to the start winding . this is why the compressor is having trouble starting under load . if you still have acess to old fridge it would be handy to reclaim it . if not you will have to find one but the size could be critical depending on the size of the compressor .

I second what don says. It's a time issue on my pump, rather than "starting with load" issue. Get your leaks to a minimum and if it's more than 4 or 5 mins before the motor needs to cut in again everything works OK.

I have 3 boards about to be made. Wish me luck.

yes ,airush geoff is correct without the start capacitor you will burn the compresor out , you may get away with it for a while because of the short run time although i would imagine the start current would be fairly high . by the way i am a sparky

I don't have an obviously visible Capacitor on my "fridge motor rig".

It may be contained within the fridge motor in my case.

If you connected the vacuum switch to the same wires that were originally connected to the thermostat, in series, I can't see why it doesn't work.

You are essentially replacing a temperature controlled switch (thermostat switch) with a vacuum controlled switch. Both turn the fridge motor on and off according to their respective criterea. Fridge gets hotter, thermo switch turns motor on. Vacuum drops, vacuum switch turns motor on.

My motor can be activated easily when opening up an air bleed valve to drop the vacuum and is instantaneous.

Cheers - Fitzy Gold Coast OZ

The frequency with which the motor comes on and off will be dependent on the vacuum loss through the bag or any lines/connections.

My unit comes on and off about every 5 or 6 minutes with the current bag and lines I made.

I reckon I may get better than that with more mucking around.

My bag is just a piece of thick clear vinyl sheeting I bought from Bunnings.

Just folded it into a tube and stuck the edges together with vinyly glue.

The ends of the resulting tube are then just rolled over and clamped with two peices of wood secured with g-clamps after the board has been inserted.

Not the prettiest bag but hey, it does the job

Fitzy GOld Coast OZ

Holy cow!

Had no idea there were so many vac-baggers lurking in the woodwork out there.

Jester56/Airush Geoff/jan/ - figured there might have been a capacitor tucked somewhere up in the fridge body along with the thermostat and light, but had no way of getting to it -> that was why I had to cut the cable leading into the fridge body; would have removed the whole lot if I could have gotten to it.

Don/nuker - yep, my vac-bag leaks pretty fast right now - figured if I could fix this well enough to allow the motor to sit for about 5 minutes before getting switched on again, I'd be able to use the vac-bag rig without fixing the motor problem; but then the thought occurred to me that if it screwed up even once during the ~8 hours the epoxy needs to set and the motor came on early it'd fry the motor -> so figured fixing the motor problem was a better solution than fixing the vac-bag leak (although I'll be tackling that one too - having the motor almost permanently on could likely fry the motor too).

Nuker - good luck with the boards! Hope to be punching out the first of mine this weekend

On having a closer look at the circuit diagrams I downloaded from the manufacturer it turns out there are two variants of the motor I've got; an HST variant and an LST variant (mine is the LST version).

**The difference between these was that the HST diagram has a Starting Capacitor and Starting relay, while the LST version has neither of these, but instead has a "PTC starting device" -> i.e. This motor may never have had a capacitor in the fridge body to get it going.

On doing a bit more research on it looks like the "PTC Starting device" is itself the capacitor or plays the role of one; here's the description I found for what the PTC starter of this manufacturer is and does:

The asynchronous motor of a single phase AC powered compressor has two windings, a main and an auxiliary winding. The auxiliary winding is powered high at start by means of a starting device, then powered down, often still utilized continuously by means of a run capacitor. The starting device of our standard PTC-starters is a “Positive Temperature Coefficient” resistor, PTC. When heated up during the start phase, the PTC almost cuts off the current to the auxiliary winding, leaving only enough current to keep itself heated to this closing level.

So if I want to restart the fridge motor quickly I'd have to instantly cool the PTC down to a level where it allows current into the auxiliary winding as soon as the microswitch turns off the motor.

Mmm... Somehow I don't think I'll be putting icepacks on the fridge-motor to allow an instant restart -> looks like fixing the vac-bag leak well enough to allow at least 10 minutes before the motor gets switched on again is the only viable way of getting this working.

On the bright side though, I won't have to go trawling for a starting capacitor or worry about the lack of one resulting in cooked windings seeing as the capacitor is already there (assuming my vac-bag leaks slowly enough - fingers crossed)!

Fitzy - followed your lead in a past thread by going the vinyl cloth from Bunnings option - difference being when I folded it into a tube I only taped the edges together with duct tape -> will try welding the edges together with an iron and a layer of newspaper above and below the PVC cloth (in one of your threads you were thinking of getting yours electrically welded to dramatically improve the seal on it?). If that doesn't work I'll follow suit and use glue.

But most of all - a great big thanks to you all for all of the input and hope this thread helps out any future vac-baggers understand their rigs and how to deal with this kind of a problem.

HOWEVER, TO ALL THOSE FUTURE VAC-BAGGERS; DON'T PUT YOUR FAITH IN ME OR WHAT YOU'VE READ HERE TO WIRE UP YOUR RIG -> GET A PROPER ELECTRICIAN TO WIRE IT UP FOR YOU LIKE I DID.

Okay, mini-rant is over now.

Thanks guys & Cheers!

under control jester leave electricity to the big boys

if your really serious about making your own boards you could buy a proper vac pump . mine cost about 600 dollars . if you figure in about 300 dollars in materials to make a board it would still be cheaper than most new boards and the next one will be even cheaper