Thread: Help needed electronics/electrical

Not all fans can be slowed via a potentiometer. Some are pulsed, with the duty cycle controlling the speed. Also, I'm guessing the board charges the batteries? Are you replacing them as well, or have some way of charging them externally?

Hi sjm
Batterys are removed and charged separately.

Fan seems to run at the correct lower speed, when connected to 3.0V supply.

At the fully charged level on the powerpack (brief contact only) the fan runs faster than the normal max speed.

Have disconnected fan from circuit board for above trials

You could try a voltage regulator kit like this one:
Voltage Regulator Kit - Jaycar Electronics

Originally Posted by Paddy

It has some fancy electronics to vary fan speed as activity increases,however as it is only used for woodwork would be happy to run at a fixed lower speed.
Battery pack is 4.8 v, but fan has 365mA and 3.57V on the label.

Motors are best controlled by 'pulse with modulation' (PWM) which is just a fancy way to describe turning things on & off quickly.

PWM is easy & cheap these days, all those cheap cordless tools have a little PWM chip in them. It might be possible to re-purpose one of those but I'm unsure they'd work at 5v. They should (in fact they should work from 3-18v). (I should check, that'd be handy to know...)

The automatically adjusting to workload part is a bit more difficult to do.

You may be able to use a resistor to limit the speed, but determining the value to use needs to be done by the trial-and-error method. The variable resistors (pots) these days aren't made to handle much current, so you can't use those unless you add a few parts.

It should be repairable, the parts it uses are fairly common.

BTW, are you sure it's 34 years old?

Bad maths! 24 years old bought it new in 1987.Used it whilst spraying weeds etc on the farm, current battery pack is about 9 years old.

The other thought I have just had is to build a new battery pack with 3.6 volts output , rather than the current 4.8V and just have a simple switch.Think this would give about the required fan speed and match the voltage marked on the fan.

Does that sound a reasonable solution?

Battery packs are only a bunch of rechargeable batteries anyway, so making a new one is reasonable. They are 1.2v, so your current pack has 4.

You can use common AA batteries, you can get them with 2500mAh capacity, so in theory (going on the motor current) they'd last about 6 hours (2500 / 365).

Jaycar sell holders, this one: 4 x AAA Side by Side - Jaycar Electronics holds 4 AA, but you can get ones that hold 3. You can get them with a cover & built-in switch as well: 4AA Switched Battery Enclosure - Jaycar Electronics. You can always add a 'dummy' battery to take up the 4th spot, or solder in a wire.

I'd try the repair route first, someone local with a bit of time might chip in. It may be a simple fault like a dry solder joint or loose connection, but looking at the parts it's using it's definitely fixable.

Thanks Dropcat

Those Jacar holders look great and will fit in the storage space OK. Was previously thinking of building my own from an old battery pack.

Will do some test runs on the workbench first