Blower Power Supply

 

19/8/2017

This is a job that has been on the 'to do' list for the last two years. I finally got around to making it today.

I had been thinking about making a variable speed power supply for my steam blowers for some time. Mine are based on the ex MOD radar cooling blowers that appeared on the surplus market a few years ago. They are superbly made as you would expect for something made for the MOD and were only about £5 to £10 each when I got mine (2006ish). People are asking silly money for them now however. I did pick up 3 more in bits so I have plenty of spare parts.

They are designed for 24volt working but work quite well on only 12 volts, which is what most people run them off. There are times though when you could do with a bit more draft but 24 volts is a bit too much and liable to suck the fire out through the chimney!

Electronic speed controllers are available from China for next to nothing so about two years ago I ordered one that had a rating of 10 amps at 30 volts. I think it was less than £5 including postage. You can't buy the components for that price to make your own.

The controller just sat around patiently and today I decided it was time to build the thing.

I remembered rescuing some nice wooden boxes from the skip when I worked for BT and a hunt around the junk in the loft produced one of almost perfect size to house the controller plus two 12 volt 4 amp hour sealed lead acid batteries. Unfortunately, they have got a bit damp at some point and the hinges and catches have gone a bit rusty.

I quickly knocked up a panel to hold the controller and the other bits from a piece of brass and asembled all the electronics on this panel and mounted it at one end of the box with the batteries at the other.

 

 

 

The variable speed works very smoothly from zero revs up to full speed. Unfortunately, the on/off switch I fitted is not man enough for the job and the contacts welded together virtually straight away! I discovered that there is a very heavy current draw when you first switch the speed controller on as there are two very large (1000uf) capacitors on the input side of the controller which charge up when first connected. I could probably get rid of one of the capacitors as the controller is fed from the batteries rather than a mains supply but I want to use it tomorrow when I go to the 2½" gauge rally at Stockport and I can't be bothered to mess around with it again at this late stage. I just switch it off by pulling one of the battery leads off!

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