adding bucked voltage to supply
adding bucked voltage to supply
(OP)
I was informed of an installation of a gate operator installation where the installers had run 10AWG wires a little over 1000' to supply a 208-230v singlephase motor. Due to the voltage drop, they installed 500VA buck transformers at the operators to get 30v or so and ran the transformer output in parallel with the supply wires, adding the voltage, compensating for the drop when the motor needed current. Is this a common practice? Is it a good or bad idea? Apparently it was more cost effective than using larger wires.






RE: adding bucked voltage to supply
And yes, that's a valid solution, weighed against the cost of wire. If the wire was already installed, you add the cost of removing and re-pulling, so it usually ends up less expensive of a fix. It would probably have cost less to use the correct size wire in the first place however.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
Could you please mark the primary & secondary polarity marks of the transformer and kindly re-upload?
RE: adding bucked voltage to supply
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
I have no experience with an autotransformer, but am vaguely familiar with the concept. Sounds like that is what one is used for, boosting the voltage...It was explained to me such that the installers 'made up' for the voltage drop by adding it back with the low voltage output of the added transformer.
RE: adding bucked voltage to supply
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
1 Transformer connected as an auto transformer.
2 There are three common connections of a voltage adjusting auto transformer;
a Step up auto transformer (boost)
b Step down auto transformer
c Step up with the secondary connections reversed to drop the voltage instead of increasing it (buck and not really an auto transformer connection)
With primary and secondary voltages of 100 volts and 10 Volts and 100 Volts applied;
The step down connection will give 90.91 Volts.
The buck connection will give 90 Volts.
The connections shown will result in rapid transformer burnout.
Look at the connections of the 30 Volt secondary winding.
Both connections of the secondary should be to either the upper line to the load or to the lower line to the load, and the jumper between the two connection points must be removed. Then, depending on the polarity, the connection will either add or subtract 30 Volts from the load voltage.
This type of voltage boost varies with the load. It is not allowed under NEC as the feeder voltage drop is more than 3%.
It will serve for fixed loads. It is not good for varying loads.
A better arrangement is to transform the voltage up to 480 Volts or 600 Volts, size the wire for the allowable voltage drop and then transform the voltage back down at the load.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: adding bucked voltage to supply
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
I get a slightly different connection than Keith. Connect windings in series so that polarity connects to non-polarity in order to step up.
Note that full load current passes through the secondary winding, but the voltage across that winding is not the load voltage. Therefore transformer VA doesn't need to match load VA.
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
The reduced voltage across the secondary tripped me up. I saw all the current going through the 2nd and jumped to conclusion.
Thanks, John
RE: adding bucked voltage to supply
Is there any dependable standard out there like H1 and X1 are always the dotted terminals?
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
The Secondary Current Rating is the transformer's non-auto rating, 500VA divided by the the secondary voltage 30V.
i.e.
238/30*500VA = 3,967VA is correct.
Of course in this mickey-mouse application described by the OP we don't actually know what the Total voltage is...
Here's a question:
In this application which end of the 10AWG run would be the better place to locate the auto-transformer?
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
I think the standards are pretty dependable this way; H1/X1 indicates polarity. Transformers don't always match the standards, though. I have a mis-marked CT, one oddball out of a set of three, with strange secondary connections as a result.
RE: adding bucked voltage to supply
I'm doing an auto-tranformer out of a 40VA transformer just today because the machine is a 230V machine and the motor brake is not releasing because the poor machine is being fed crappy 208V e.g. 203V and the brake demands 205V pulsating DC out of a bridge rectumfryer.
Keith Cress
kcress - http://www.flaminsystems.com
RE: adding bucked voltage to supply
RE: adding bucked voltage to supply
Indeed!
Keith Cress
kcress - http://www.flaminsystems.com