[time-nuts] HP 5370B dropping mains voltage...

Robert LaJeunesse rlajeunesse at sbcglobal.net
Sat Jul 6 21:13:28 EDT 2013


I used an old thyratron filament transformer from a computer tape drive to compensate for low line voltage in Detroit. Even though the transformer was rated 10A it ran our old room air conditioner just fine. From the core size it seemed more like a 200W transformer, and it never gave any problems. So just make sure the secondary current rating of the transformer you get exceeds your expected load current some and heating should not be a problem. Better yet, have it exceed your mains fuse / breaker rating some. 

As for insulation resistance any quality filament transformer will have a secondary insulation voltage rating called out, as long as it exceeds the mains voltage you should have no concern. Beware of so-called "rectifier" transformers that may not have a published insulation rating, they may not be suitable for your task.

For how one company promotes and wires their buck-boost transformers see http://www.signaltransformer.com/sites/all/pdf/ICT.pdf

Another possibility is to find a transformer with a 230V primary having a 208V tap (not too uncommon in the US). Feed the 230V point, use the 208V tap for your loads. Be aware that in this case the transformer would need a primary current rating to exceed your your load, so the transformer would be much bigger than the filament buck-boost transformer approach.   

And do package things so there are no exposed transformer leads or terminals. My transformer had wire leads, I was able to button everything up in a 4" x 4" x 2" electrical wiring box, and use common 15A pigtail connectors on short cables for mains and load.

Good luck,

Bob LaJeunesse

> From: Mark C. Stephens <marks at non-stop.com.au>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Saturday, July 6, 2013 8:26 PM
>Subject: Re: [time-nuts] HP 5370B dropping mains voltage...
>The elephant in the room thing with me is SAFETY :)
>I mean, can this be a fire hazard, what about the insulation breakdown on the secondary winding etc..

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