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blazinbrush · 04-12-2011, 03:21 AM

I'm working on a Brutus clone that uses three Honeywell VR8200 gas controls. I'm trying to figure out the amount of power required for the 110VAC->24VAC transformer. Although it will probably never happen, I'd like to have a transformer big enough to run all three gas controllers at the same time. The manual for the VR8200 (found here) claims the following:
Hold-in current: 300mA max
Drop-out current: 250 to 90 mA
Thermostat heat anticipator setting: 0.5A.

Do I need to include the anticipator in overall current consumption, which would basically mean that each VR8200 uses 800mA? If so, then I'm looking for at least 2.4 amps of 24VAC. That would mean a transformer at least 60VA?

I'm pretty sure I know what the heat anticipator does (i.e. account for overshoot), but I don't know how it works, so I don't know how the 0.5A spec applies to the overall power consumption.

Thanks,
BB

**Namako** · 05-16-2013, 04:07 AM

Humm... I have the same question, and found your post in my search. Did you ever get an answer, or decide on a solution?

**Yellowirenut** · 05-16-2013, 09:49 AM

http://www.amazon.com/White-Rodgers-120-240V-24V-75VA-Transformer/dp/B004IWEKBG/ref=sr_1_7?s=hi&ie=UTF8&qid=1368697607&sr=1-7&keywords=TRANSFORMER+120V%2F75VA

You should then have plenty of push.
It also has a built in pop fuse.
It is available at many places I was just using amazon for reference.

**Namako** · 05-16-2013, 09:57 AM

I guess my question was more related to whether the heat anticipator setting (0.5A) actually needs to be considered in the calculations, and whether the draw is on whenever the gas valve is open.

**reynolds5520** · 05-16-2013, 01:11 PM

Short answer, you need a transformer that can supply at least 300mA per valve at 24 VAC. (A higher amp rating is O.K., the valve will only use the amps it needs.)

Longer answer, the heat anticipator is a resistive heating circuit built into a thermostat. When a furnace is running, the current of the valve runs through the anticipator. The anticipator heats up the thermostat so that it kicks the furnace off before the room air is all the way up to the set point. This helps to prevent overshoot since the furnace blower will keep adding heat to the room, even after the burner is off, until the furnace has cooled to the fan off point.

The listed spec for the heat anticipator setting allows an installer to adjust the anticipator in the thermostat to an initial set point to match the current of the valve. The anticipator may then get further adjusted to eliminate overshoot or short cycle times.

In other words, the heat anticipator spec isn't an additional load in the valve, and isn't important to this application.

**Namako** · 05-16-2013, 09:22 PM

Excellent answer!!! Thanks for that!!

If the 0.5A laod is not relevant to our applications, it would appear that most of the 24VAC transformers used in these applications would work to drive 2 or 3 gas valves.

I purchased the Honeywell AT72D transformer that puts out 40AV at 100% power, and I'm hoping it will drive two Honeywell VR8200A gas valves. Looks like it will work just fine, doesn't it?

blazinbrush · 05-17-2013, 12:48 PM

Agreed, nice answer, reynolds! That makes perfect sense.

I ended up not finding the answer to my question so I just bought one big enough to supply the additional 500mA.

For reference, here's the one I bought:
http://www.mpja.com/24V-4A-Center-Tapped-12-0-12-Transformer/productinfo/7845%20TR/

It was less expensive than many 40VA transformers I found. I've been using it for a year and half now and it's been doing it's job. It will drive three VR8200 controllers.

BB

blazinbrush · 05-17-2013, 12:54 PM

Yes, Namako, I would say the AT72D should work just fine. Looks like it's 24VA, which should be plenty to run 2 controllers. Looks like HD also has a Johnstone PF42440 40VA transformer for $12.59.

**kladue** · 05-17-2013, 02:50 PM

For a single VR8200 you should use a 40Va transformer, lower Va transformers will open the valve but will heat up when running for more than a few minutes. For 2 valves a 75Va transformer would be appropriate for both valves operating at the same time.
What appliance builders install is meant for exposed air cooled operation and can be lower Va rated, when installed in a non ventilated control panel you need the higher Va rated transformer that is not as heavily loaded because of limited heat dissipation inside enclosure.