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Old 07-07-2017, 06:53 PM   #1
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120v Surge Protection - AC control transformer failure

I have just finished troubleshooting our Salon AC unit. It is a 16000 btu unit, 120v AC. It is only 3 years old, Ocean Breeze unit.

It turns out the 120/24 vac control power transformer was bad. I contacted PO and he said he had that happen also.

We just finished a few days at anchor over the 4th and were running our generator for quite a bit of time. So I am guessing that some sort of power surge blew the control transformer.

Anyone ever deal with this? I am contemplating the installation of some sort of surge protection.
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Old 07-07-2017, 07:05 PM   #2
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Have you Allen the manufacturer and asked a teak rep his opinion?
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Old 07-07-2017, 07:08 PM   #3
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Ok I put the beer down, have you called the manufacturer and asked a technical representative him opinion?
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Old 07-07-2017, 07:35 PM   #4
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I think "power surges" are one of the industries great excuses for brushing off failures.

Transformers are generally very robust. I would look closely at the loading on it. What is it powering and is it overloaded? It shouldn't be an expensive part, so before installing any sort of surge protector, I would just buy a second one and carry a spare.
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Old 07-07-2017, 07:56 PM   #5
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Which side opened? Check with a VOM/continuity on the 120V side and the 24V side to see which one doesn't read continuity. That's the side that opened. If it's the 24V side, chances are a surge protector won't help much, I'd expect the connected load may be at the VA limit of the transformer. Conversely, if the 120V side opened, a surge protector may help. But being the load side is lighter gauge wiring, it's what usually fails. You could use a higher VA rated transformer. 40VA is an industry standard for control circuits.
You can check the amp draw of your 24V control circuit if you have an amprobe, take a couple of wraps around the jaws to get the reading to scale better - divide the reading by the # of wraps. You should read less than 1.6A (AC amps- VA=Volts * Amps). If you're close, you could be overloading the transformer. If that's the case, you could go to a 70VA transformer, I'd put a 3A inline slo-blo fuse in the 24V supply just to be on the safe side.
Don't overlook the possibility that there may be a component over-drawing current intermittently, that could pop the transformer.
Since this is a repeat event, you need to find the why in the equation in order to solve the problem. Don't use a higher VA rated transformer simply to bypass the troubleshooting process- only if you determine that the connected load exceeds the transformer's capacity!
As a preventive measure, you could insert a resettable 1.5A circuit breaker in the 24V supply, could prevent a breakdown situation when you're not near parts and it's hot!
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Old 07-08-2017, 07:23 AM   #6
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Originally Posted by Maerin View Post
Which side opened? Check with a VOM/continuity on the 120V side and the 24V side to see which one doesn't read continuity. That's the side that opened. If it's the 24V side, chances are a surge protector won't help much, I'd expect the connected load may be at the VA limit of the transformer. Conversely, if the 120V side opened, a surge protector may help. But being the load side is lighter gauge wiring, it's what usually fails. You could use a higher VA rated transformer. 40VA is an industry standard for control circuits.
You can check the amp draw of your 24V control circuit if you have an amprobe, take a couple of wraps around the jaws to get the reading to scale better - divide the reading by the # of wraps. You should read less than 1.6A (AC amps- VA=Volts * Amps). If you're close, you could be overloading the transformer. If that's the case, you could go to a 70VA transformer, I'd put a 3A inline slo-blo fuse in the 24V supply just to be on the safe side.
Don't overlook the possibility that there may be a component over-drawing current intermittently, that could pop the transformer.
Since this is a repeat event, you need to find the why in the equation in order to solve the problem. Don't use a higher VA rated transformer simply to bypass the troubleshooting process- only if you determine that the connected load exceeds the transformer's capacity!
As a preventive measure, you could insert a resettable 1.5A circuit breaker in the 24V supply, could prevent a breakdown situation when you're not near parts and it's hot!
Or....

You could assume the ac unit has a electrical design flaw and buy one from westabo, or marinaire or whomever to alleviate the risk of fire that popping transformers bring with them. No offense against Maerin, but you shouldnt have to redesign their unit.
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Old 07-08-2017, 08:13 AM   #7
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Quote:
Originally Posted by twistedtree View Post
I think "power surges" are one of the industries great excuses for brushing off failures.

Transformers are generally very robust. I would look closely at the loading on it. What is it powering and is it overloaded? It shouldn't be an expensive part, so before installing any sort of surge protector, I would just buy a second one and carry a spare.
Agree totally. I design industrial surge resistant systems and frequently test transformers, power supplies, and other circuits to 4 and 5kV levels. I've never seen surge take out a transformer. They could run hot, corrode or have insulation failures. I would likely simply find a better quality transformer. Does it run too hot to touch? There are tons of 120 to 24V control transformers out there. But, look for Class 2 (safer) device.
Now, if a semiconductor failure took out the transformer, then the conversation will be different. Is the xfrmr the only defect?
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Old 07-09-2017, 08:39 AM   #8
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Or....

You could assume the ac unit has a electrical design flaw and buy one from westabo, or marinaire or whomever to alleviate the risk of fire that popping transformers bring with them. No offense against Maerin, but you shouldnt have to redesign their unit.
Absolutely no offense taken, you're exactly on the money. I would have been more appropriate to stress that a failed transformer is not normal, more important is to find WHY it failed. Once could be a fluke, twice is an undiagnosed fault.

Thanks for keeping me on point.
Steve
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