I have a heavy duty transformer rated at 22oVAC 500W input and 24V 20amp output. The secondary has no centre tap. I want to use the output to power 12v portable drills and also to be able to use it as a power supply for a 12DC model railway and as a base for a bench power supply. Are all these things possible to do?

 

They're possible, but it may not be the easiest/cheapest solution.
To get down to 12VDC efficiently would need a switch-mode converter. It may be easier/cheaper to source a 220VAC/12VDC converter than a 24VAC/12VDC one (I haven't checked).
We don't know your bench supply spec.

 

Since the 12VDC Model Railway is likely mainly an inductive load, isn't there protection if the switching power supply necessary?

 

Thank you both for the replies. My main concern is to power 12v portable drills as my now very old rechargeable batteries only hold a charge for about a quarter of an hour at most and the battery types I have have been changed by the manufacterers (Bosche) so I am left with several drills in full working order only without a convenient power source

 

some of the portable drills have variable speed, ac would not work on them, only dc.

 

I have a heavy duty transformer rated at 22oVAC 500W input and 24V 20amp output. The secondary has no centre tap. I want to use the output to power 12v portable drills and also to be able to use it as a power supply for a 12DC model railway and as a base for a bench power supply. Are all these things possible to do?

You could look at modifying the secondary, either take the whole secondary off and wind a suitable gauge 12v secondary, or just take turns off, in most cases for motors and relay equip, you do not need a cap smoothed supply, which in that case use 12AC rectified, if you cap smooth it, you need 8.5v AC. it most likely will work out to ~2turns/volt.

some of the portable drills have variable speed, ac would not work on them, only dc.

Yes, the AC powered are Universal, the portable/battery operated are P.M. DC brushed.
Max.
,

 

Power drills use series motors which run equally well on DC or AC.

So all you would need is just a 220V/12V transformer. There is no need to rectify the output.

Unfortunately you have a 220V/24V transformer without a centre tap!

However, it can be used if you have access to 110V or have a dimmerstat to reduce the 220V to 110.

Regards,

Nandu.

Agree on the series motor, but doubt if the DC speed regulator behind the trigger would be happy with the AC. If the transformer laminations are bolted together and you have the time, dismantle it one weekend and rewind the secondary or centre-tap it, then use 2-diode rectifier with centre tap as common.