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vac pump (a fridge compressor) problem

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downunder
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vac pump (a fridge compressor) problem

Postby downunder » Sun Nov 26, 2017 2:18 pm

Hi guys

I've burned my old fridge compressor and got a new one. This one has a 'starting device' (looks like a huge capacitor, duno if the starting device is actually a relay, probably it is, but my old compressor did not have this big capacitor), and on a sticker it says do not start without the starting device.

Now, the problem is, this 'device' is delaying start for quite some time, like 3-5 mins after poweroff, and my vacuum is not holding that long!

And if left running, pulling half vacuum only, the compressor is heating up quite fast, like in 10mins!

My old pump was starting at any time, every 30 secs if needed, going warm after hour or so. This one? Hmmmm.

Can I remove the capacitor? Is the capacitor causing a delay problem or a relay? Any thoughts?

Thanks

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Re: vac pump (a fridge compressor) problem

Postby faklord » Sun Nov 26, 2017 5:42 pm

My guess is it a starting capacitor
https://en.m.wikipedia.org/wiki/Motor_capacitor
1) I doubt that this is causing your delay.
2) I expect the motor would just not start at all if you disconnected it (and a stalled motor will get hot!). In fact I wonder if the delayed start is actually because the start capacitor is faulty or not being reliably connected?

3-5 mina is a long time. Possibly a heating effect? Are you sure the compressor hasn’t run dry on lubrication..could try squirting some oil into the inlet...I do this periodically. However this will only help the compressor part..the motor bearings would be much harder (impossible?) to get at.

If they are easy to find, You might be better off just picking up another compressor.

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Re: vac pump (a fridge compressor) problem

Postby rynhardt » Sun Nov 26, 2017 8:38 pm

Your compressor's thermal cutout switch could be more sensitive than the old one. It's a little bimetallic strip that opens the circuit when the heat increases.

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Re: vac pump (a fridge compressor) problem

Postby downunder » Mon Nov 27, 2017 2:55 am

Thanks guys.

Looks like the problem is only with a vacuum. It does start almost immediately when not pulling a vac and not getting hot.

Duno. In Australia nothing is cheap. Paid $80 for this one.

Any experience with a aircon rotary piston compressor? Are they more noisy and can they start every 30-60 secs? If I'll need to buy a new one I would rather go with something not spitting oil and with more cfm so can use it for touch up paint brush

D.

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Re: vac pump (a fridge compressor) problem

Postby downunder » Tue Nov 28, 2017 3:15 am

Heya

looks like I've got some good news :)

Never tried this before but did run this compressor continuously last night! My impression was that the pump might go really hot if doing so, but it's not actually. Only warm. Either way, did run a small PC fan to cool it just to be safe.

Very quiet, can't be compared with a proper vacuum pump which I've got as well. So now looks like this is a go. No power cycling, no on/off switches with a timer or anything.

Happy days. The HF is getting there.

D.

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Re: vac pump (a fridge compressor) problem

Postby KerryBara » Wed Dec 06, 2017 8:06 am

Hey Downunder,

Isn't it simpler to just fix your bag?

Also, if you get a slower curing resin, you'll relieve a lot of the time pressure and you'll give yourself more time to properly seal the bag.

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Re: vac pump (a fridge compressor) problem

Postby downunder » Wed Dec 06, 2017 8:29 am

Hi Kerry

if is not about sealing the bag so much. The bag is sealed, sometimes better sometimes not so good.

It is about topping the vacuum from time to time. If the pump is starting in ie 3-5 mins after being off, but vac holds only for 2-3mins, there is a risk of loosing a vac and destroying a project. It did happen before.

Hence I would rather run the pump for hours than risking the project.

BTW, using a tongue and groove for sealing a bag, stopped using anything else.

D.

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Re: vac pump (a fridge compressor) problem

Postby KerryBara » Fri Dec 08, 2017 11:35 am

downunder wrote:
Wed Dec 06, 2017 8:29 am
Hi Kerry

if is not about sealing the bag so much. The bag is sealed, sometimes better sometimes not so good.

It is about topping the vacuum from time to time. If the pump is starting in ie 3-5 mins after being off, but vac holds only for 2-3mins, there is a risk of loosing a vac and destroying a project. It did happen before.

Hence I would rather run the pump for hours than risking the project.

BTW, using a tongue and groove for sealing a bag, stopped using anything else.

D.
I understand what your issue is.

So I'm doing infusion only, which means i have more time to make sure the bag is properly sealed, but I can leave my bag overnight and it'll still hold the vacuum (not every time, but definitely longer than 2-3 min).

If I was in your shoes, I'd probably find a solution for the pump just in case anyway.

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Re: vac pump (a fridge compressor) problem

Postby faklord » Fri Dec 08, 2017 5:31 pm

Downunder,
I would be a bit cautious about regularly running a fridge compressor ‘dry’ overnight. My understanding is that in normal use the refrigerant provides some circulating lubricant.
As previously stated, I periodically squirt some oil in the inlet pipe. To prevent spitting oil, the exhaust has a bit of cloth tied over and a drip can underneath.
Ideally you want an adjustable pressure switch, to switch your compressor on/off and set/control the vacuum. Like many others I knocked something up with and old auto advance/retard diaphragm, microswitch & spring but I’d don’t see why something like this wouldn’t do the job https://www.veneersupplies.com/products ... 8-NPT.html though you may want to also add a gauge.
For vac bags I use vacuum storage bags eg https://www.amazon.co.uk/DIBAG-COMPRESS ... acuum+bags. I have, so far, had a 100% sealing success rate with these, they are reusable, easy to open-adjust-reseal. I even do boards in these! The only downside is you need to make an adaptor to go from your vac pipe to the bag ‘valve’.

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Re: vac pump (a fridge compressor) problem

Postby gilana » Sat Dec 09, 2017 1:51 am

Without going into too much detail (A photo would help) There are start devices on some compressors, but then there will be one or two capacitors as well.
If one cap only it might have a start and a run winding. The Start device is a relay that is NC and as the inrush current starts it goes open, but that is enough time to set up the flux in the stator to get the rotor spinning. In a nutshell, if its got a start "helper" it does not like to start often, or restart, or start with a high relative head pressure. The upside is that they are designed to be efficient while running...so cooler, quieter and less amperage. This is good.

Best leave it running longer periods and perhaps have a vacuum tank (PVC pipes) to avoid the fluctuations, like a huge cushion on the vacuum. I would also consider an in-bleed to regulate the vacuum and a water manometer to measure really accurately. The In Bleed can be a clamp on a hose but with a spring between the clamp and the hose so that it will adjust for temp/density etc. An oil trap is an easy addition, all you have to do is make a wider diameter exhaust pointing straight up, and put a brass pot scourer inside it. The increase in diameter will reduce velocity oil will get trapped. Just thinking about it, a small pipe with valve from there to the fill connection will suck the oil back into the sump.

The computer fan is an excellent idea, especially at the bottom, because thats where the oil is.


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