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Author Topic: Startomatic wiring advice  (Read 645 times)

ajaffa1

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Re: Startomatic wiring advice
« Reply #15 on: June 19, 2019, 01:13:42 PM »
Hi Tony, it comes as no surprise that WORK is a four letter word! Your ambition of building an SOM  can wait until the next power outage.

Take good care,

Bob

BruceM

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Re: Startomatic wiring advice
« Reply #16 on: June 19, 2019, 03:53:51 PM »
Bob, I respectfully disagree. While there is a path, the field coil resistance will limit the current.  There will only be few amps current through the field windings, and that's all the bridge rectifier must handle.





apbedford

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Re: Startomatic wiring advice
« Reply #17 on: June 26, 2019, 05:35:28 PM »
Hi Bob

I finally made a bit of time to inspect the control panel. It turns out that the D1 relay, which starts the whole sequence, was U/S - it looks as if it has been overheated in the past.

I thought that I would rewind it, but just wanted to check with you whether you happened to know the specs. My original had 100 ohms stamped on it, and I estimate that I removed about 245 meters of enamelled wire, trying to measure it as I went.

Anyway, to make the numbers work, I'd need to use 245 m of 0.224 mm wire (31 gauge) - giving about 100 ohms, but I'm pretty sure that what was on there originally is finer than this - I make it somewhere between 0.18 mm and 0.20 mm (33/32 gauge). 245 m of this would give me between 135 and 160 ohms.

Any comments? I'm sure that you guys have had to do a few rewinds like this!

All best
Tony

apbedford

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Re: Startomatic wiring advice
« Reply #18 on: June 26, 2019, 06:41:07 PM »
On second thoughts, maybe the original was 0.224 after all, which would make sense. Difficult to tell even with calipers and feeler gauges.

ajaffa1

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Re: Startomatic wiring advice
« Reply #19 on: June 27, 2019, 12:43:25 AM »
Hi Tony, the best way to work out how much wire you require is to weigh how much wire you have removed. Identifying the wire gauge can be tricky due to the thickness of the insulating varnish, try burning it off with a cigarette lighter. Once you have identified the gauge wind the coil until you have 5% more copper than you took off. Now measure the resistance and remove wire until you get to your target of 100 ohms. I found it difficult to find suitable cloth insulation tape to cover the coil. I found that micropore surgical tape was a good substitute and once varnished looks identical to the original.

If the coil was burned out it is almost certainly because the old selenium rectifier failed sending 240/110 volts AC through it.

Bob

apbedford

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Re: Startomatic wiring advice
« Reply #20 on: June 27, 2019, 09:42:28 AM »
Hi Bob, thank you, I was wondering how to adjust the winding - excellent method.

Iíve ordered the wire, so will see how I get on. Any tips like that much appreciated!

All best
Tony

apbedford

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Re: Startomatic wiring advice
« Reply #21 on: July 01, 2019, 02:04:58 PM »
Hi Bob

I've rewound the coil to 100 ohms as per original: just wanted to make sure what the rating for the load resistor DR would need to be to drop the initial voltage in the detection circuit from 24 to 12, as my coil is definitely from a 12V setup: you had originally said 5W, 6.8K ohms, which I have, but unfortunately being hopeless at electrics myself, I would have thought that it should be a far lower resistance. Presumably any load resistance has to be included in the calculation, so: coil resistance, plus load resistance, plus load resistor DR. I wondered if you would mind just explaining how it works!

All best
Tony

apbedford

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Re: Startomatic wiring advice
« Reply #22 on: July 01, 2019, 02:21:39 PM »
Sorry, meant Detection Circuit resistance, DR

AB T