# 50VAC bench top power supply?

#### Ed. M.

Joined Nov 8, 2017
41
Hi,

For my project I need to power a coil/solenoid with 50V AC. I'd like something I can plug-in to a wall socket, but I can't find anything to fit the bill at a reasonable cost (ideally < $100). I assume all I'd need is a step-down transformer that's plug-able into a wall, but haven't been able to find anything like that (if it's easily and safely build-able, please let me know and provide links to needed parts). Any suggestions would be greatly appreciated. Thanks. - Ed. #### bertus Joined Apr 5, 2008 21,054 Hello, How much power would the solinoid take? As you said a transformer would be the way to go. Bertus #### KeepItSimpleStupid Joined Mar 4, 2014 4,389 24 Vac transformers are common. You can place transformer windings in series to add and subtract voltages. An unloaded 24 VAC transformer will probably be 10% higher in voltage. 24 VAC 40 VA energy limiting and non-energy limiting transformers are extremely common for HVAC. https://www.supplyhouse.com/Packard...8-240V-Primary-24V-Secondary-40VA-Transformer A 24 VAC, dual secondary at 0.6A https://www.alliedelec.com/product/hammond-manufacturing/6k184vfl/70009039/ Not enough info to help you find stuff. Current, duty cycle, location (country) or what the native power is. Thread Starter #### Ed. M. Joined Nov 8, 2017 41 Hello, How much power would the solinoid take? As you said a transformer would be the way to go. Bertus I'm not exactly sure how much power. It's takes 50V AC to fire, but how much current I really don't know. Thread Starter #### Ed. M. Joined Nov 8, 2017 41 24 Vac transformers are common. You can place transformer windings in series to add and subtract voltages. An unloaded 24 VAC transformer will probably be 10% higher in voltage. 24 VAC 40 VA energy limiting and non-energy limiting transformers are extremely common for HVAC. https://www.supplyhouse.com/Packard...8-240V-Primary-24V-Secondary-40VA-Transformer A 24 VAC, dual secondary at 0.6A https://www.alliedelec.com/product/hammond-manufacturing/6k184vfl/70009039/ Not enough info to help you find stuff. Current, duty cycle, location (country) or what the native power is. I don't know the current, I just know it's a 50V AC powered coil from an old Bally EM pinball machine. Part no. is 25-GG-7. I'm in the US so 110/120V from the outlet. That second link looks interesting as it seems to output 48V AC which should be sufficient. As far as current goes the circuit is protected by a 10 amp fuse so the current can't be more than that. #### JohnInTX Joined Jun 26, 2012 4,358 One of the more handy setups on my bench is a variac plugged into an isolation transformer (for safety). The variable AC output serves many purposes and many actually go above the line voltage a bit - useful for high line tests. I haven't used any of the cheapies on Amazon but worth a look. Search on ISOLATION TRANSFORMERS and VARIACS. #### KeepItSimpleStupid Joined Mar 4, 2014 4,389 Just saw on http://www.actionpinball.com/parts.php?item=B-25-925 that they're 7 ohms if that helps. That would generally mean that the solenoid would draw about 7.14A (48/7) BRIEFLY. An isolated variac (variable autotransformer) with meters is not a bad thing to have. I probably built mine when I was 10 YO, some 40+ years ago. I have a 1000 W isolation transfromer that I paid like$10.00 for and that sits external. Then a 3A variac and a 120V analog meter for voltage and current. I did create a bypass so I do have 10A of isolated 120 available, but 3A to bring say a TV or amplifier up slowly.

It would be a good idea to put two fuses on a home built unit. One on the rear panel and one on the front. I fused the front. With a variac, you MUST fuse the wiper.

I did put a NEMA 5-15 outlet and binding posts on it.

The auction site has power conditioners by OneAC, now Powervar, that are essentially isolation transformers

One modification I would make today would be have a light anytime it's on.

#### SamR

Joined Mar 19, 2019
2,921

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,389
Your on the right track, but not enough current.

On ebay search for a CB1120. It's 16A. they will work too.

This https://toroid.com/Products/Medical-Isoboxes/Domestic-CN-Series gives you an idea of what your up against.

I used something like this: http://www.surplusindustrialsupply....r-sale-dongan-750kva-transformer-tra1840.html
which is 750 VA, not >1000 VA. You have to add an outlet, power cord and MAYBE a fuse and it doesn't look pretty. I was matching the isolation with a 10 A variac.

But you need about 330 W.

You had 48V and 7 Ohms, so you can get power 230 W. Watts and VA are not quite Identical, but close enough.

48/7 is 6.85 A or so and that means 6.85 A on the WIPER, so a 10 A Variac is OK.
You can use >~330W isolation transformer. That would mean, you can use it on 330W/120V or something that draws 2.75 A at 120 Vac,

Trying to cut costs.