ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Smoke & mirrors?
by JoeTestingEngr - 09/19/20 10:00 PM
Pool Lights?
by Papa - 09/18/20 05:26 PM
Ever been afflicted by Gout?
by mbhydro - 09/15/20 05:50 PM
Questioning the electrical norms
by gfretwell - 09/13/20 01:17 PM
120/208 gives 240? please clarify
by NORCAL - 09/13/20 01:08 AM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
0 registered members (), 18 guests, and 13 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
control transformer #8967 04/10/02 02:09 PM
Joined: Dec 2001
Posts: 50
J
Joe Carpenter Offline OP
Member
What is the downside to using a 240v primary/ 24 secondary transformer for a 120v primary/ 12v secondary application? I know it works but is there a reason I should not do it if I size it for the correct kva? I need to use it to power 12volt automotive lights.
Thanks

Work Gear for Electricians and the Trades
Re: control transformer #8968 04/10/02 08:10 PM
Joined: Apr 2001
Posts: 83
D
donles Offline
Member
Hi Joe,
I don't think there is a down side as long as it's rated properly. The rest is turns-ratio - i.e. they are the same.
Don

Re: control transformer #8969 04/10/02 11:35 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
Remember that you need to halve the transformer VA, too. Current remains constant.

Re: control transformer #8970 04/11/02 11:27 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
Member
Are you planning to use a Transformer with single windings on both sides [Primary and Secondary]? And this Transformer is rated only as 240 Pri / 24 Sec.?

If the Volt-Amp rating [VA or KVA] was 250 VA for this Transformer, and you plan to drive it at 120 VAC, only load it up to 125 VA. Otherwise it will burn out.

125 VA @ 12 VAC would be around 10.3 amps.

Falling under the 125 VA rating assures the smoke remains inside the windings [Linked Image]

If the transformer has "Split Windings", then connect the windings as needed to be driven from 120 VAC and output of 12 VAC.

If only one side has split coils, leave the arrangements as 240 VAC Pri / 24 VAC sec.

I used a very large rating for a Control Transformer [250 VA]. They are usually around 25 VA min. to 100 VA max., with 50 VA being a normal rating.

If you plan to drive an Automotive Headlamp, you should consider a larger Transformer.

Scott SET


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
RH1
RH1
California
Posts: 22
Joined: August 2009
Show All Member Profiles 
Top Posters(30 Days)
Trumpy 8
NORCAL 3
Popular Topics(Views)
269,940 Are you busy
204,371 Re: Forum
192,590 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3