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RCMAN46

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Posted: 07/20/20 10:44am Link  |  Quote  |  Print  |  Notify Moderator

The Hughes Autoformer I have has triacs that determine which transformer tap is active. As such measuring dc resistance between hot input and the hot output may be something much higher than expected as you are going through a triac.

There will be some resistance between the neutral and hot due to the voltage sensing circuit in the Autoformer.

The neutral lead goes direct from the input to the output so it should measure very low in dc resistance.

When I first received my Autoformer Hughes had reversed the output leads which resulted in the hot lead being on the neutral of the output. Also my trailer was wired wrong in that the ground and neutral had been bonded. This resulted in the trailer frame connected to the hot lead. Thus you will receive a shock if you touch the trailer while standing on the ground outside the trailer.

This can be checked on the Autoformer. As stated above the neutral goes direct through the Autoformer. Thus input neutral to output neutral should be a very low dc resistance. The hot goes through the transformer and because of the triacs there will be some resistance measured between input and output hot leads.

There should be infinate resistance between ground on the Autoformer and either the hot or neutral lead.

I discovered my problem when my Hughes was new and Hughes replaced my Autoformer under warranty.

CA Traveler

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Posted: 07/20/20 11:09am Link  |  Quote  |  Print  |  Notify Moderator

A shock from the frame is a resut of 2 probems:
1. You have a ground fault (leak to the frame-ground.
2. You have a open (or high resistance) ground to earth ground connection.

The autoformer could have both. Open the autoformer and check all connections which should be clean and tight.

RV plugs and RV pedestals are notorious for poor maintenance, you've already identified at least one bad plug.


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rfaulkner99

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Posted: 07/20/20 11:43am Link  |  Quote  |  Print  |  Notify Moderator

Let me add one more detail to the mix. Before I discovered the shock issue, my EMS shut off the power while the Autoformer was connected due to an open ground (according to the error code). I checked the Autoformer and it was extremely hot to the touch - I attributed this partly to the fact that it was the hottest part of the day with temps in the upper 90s and the fact that I had placed a small trash can over the Autoformer to protect from rain, and it had very little if any ventilation. After I removed the Autoformer, the open ground condition went away.

A few hours later after I had let the Autoformer cool down, I plugged it back in and just positioned it under the RV to protect from rain with better ventilation. It seemed OK until the shock incident.

CA Traveler

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Posted: 07/20/20 11:54am Link  |  Quote  |  Print  |  Notify Moderator

Water on the ground increases the likelyhood of feeling a shock with faulty equipment. The shock potential may have existed prior to the rain.

wa8yxm

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Posted: 07/20/20 04:01pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

Autoformer is not an isolation transformer but rather one big coil with several tap points to get the different voltages. How would it work with an open circuit? There is no power switch.

If this is about the plug melting, this is fairly common during high usage as many pedestal connectors are worn, pitted, dirty and corroded causing a poor connection and some heat.


I am not sure if the Autoformer is an Autotransformer or a tapped transformer.


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DrewE

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Posted: 07/20/20 08:07pm Link  |  Quote  |  Print  |  Notify Moderator

wa8yxm wrote:


I am not sure if the Autoformer is an Autotransformer or a tapped transformer.


Hughes actually claims it's not an autotransformer, in as much as it has separate line and load windings. In my opinion, and from what all I can suss out about how they're constructed, Hughes is being misleading in making that claim: while the transformer itself presumably does have separate windings for the input and output, the two sets of windings are connected together when it's in use and so wired in an autotransformer configuration. (Buck/boost transformers are pretty standard components used in e.g. some industrial installations, and there's nothing to suggest that the Hughes device is anything much different than one of them along with some associated switching circuitry.)

I think their response to the recent NEC changes that prohibit autotransformers for RV park use is also rather telling. They have come out quite vocally against these changes, saying basically that they are pointless and senseless and were promoted by parties with less than pure motives, and then continue on with "but they don't apply to our products anyhow." While the first bit may well be true, and I tend to agree that it's a rather bizarre restriction as stated, why would they be so vocally against it if they were certain their product was not affected by the new code?

(As an aside, the NEC has long had a prohibition on the use of autotransformers in RV converters which at a casual glance might seem to apply a little more broadly. That's unrelated to autoformer/voltage booster use.)





wa8yxm

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Posted: 07/21/20 05:04am Link  |  Quote  |  Print  |  Notify Moderator

I have wired a buck (As I recall) transformer not an auto-transformer (Though I have small ones for device testing)

The transformer had two windings ONe wired "In phase" with the primary transformer in the device and the other (The buck coil) out of phase .

Hughs is saying that is how they are doing it.. I won't argue. There is a very good reason to do it this way But without opening it up and taking measurements I can't be sure what they did. Thus I will take their word for it for now since they make the thign.

IF you have an internal schematic I can look at then I can tell you for sure.
But I'm not opening the case.

Lynnmor

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Posted: 07/21/20 06:52am Link  |  Quote  |  Print  |  Notify Moderator

I think that the old code only pertained to the campground so that autotranstormers wouldn't be used in the supply side, that is my interpretation. The new code may be going after the customers for various reasons. Try reading the old and new to see what I am guessing at.





RCMAN46

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Posted: 07/21/20 08:20am Link  |  Quote  |  Print  |  Notify Moderator

wa8yxm wrote:

I have wired a buck (As I recall) transformer not an auto-transformer (Though I have small ones for device testing)

The transformer had two windings ONe wired "In phase" with the primary transformer in the device and the other (The buck coil) out of phase .

Hughs is saying that is how they are doing it.. I won't argue. There is a very good reason to do it this way But without opening it up and taking measurements I can't be sure what they did. Thus I will take their word for it for now since they make the thign.

IF you have an internal schematic I can look at then I can tell you for sure.
But I'm not opening the case.


I will settle for a wiring schematic of your two winding transformer that is not an auto-transformer.

Cummins12V98

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Posted: 07/21/20 09:30am Link  |  Quote  |  Print  |  Notify Moderator

If you want a FACTUAL answer simply contact AutoFormer!


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