Incapacitated -- trying to wire up a small 35v 3300 mcf electrolytic to a little 18vdc @ 2A motor

hsazerty2

Joined Sep 25, 2015
32
Maybe the output current of the transformer is not intended to drive directly the motor, it has first to charge the battery for quite a long time, then the battery will drive the motor by a greater current but for a smaller time.

Can you give us a little more information about the battery you intend to remove ? like :
- Capacity in mA.h.
 

ian field

Joined Oct 27, 2012
6,536
If there is little or no internal filtration then shunting the PSU will increase the EMF (the limiting factor being 2^.5) -- That said, it sounds as if the PSU is not supplying sufficient current -- are you quite certain the cap is paralleling the PSU and load?

Best regards
HP
If the transformer is rated to charge a battery that will run the motor - it is unlikely to supply enough current to run the motor directly.

The exception being if the charger is advertised to be capable of running the motor at the same time as charging a flat battery.

Its something I always ask when buying a rechargeable shaver - most won't run only on the charger, the ones that can usually cost a fair bit more.

I'd be pretty annoyed if I paid the higher price and couldn't plug the charger in and carry on shaving when it runs down.
 

Thread Starter

Dynamo1

Joined Nov 19, 2015
15
Maybe the output current of the transformer is not intended to drive directly the motor, it has first to charge the battery for quite a long time, then the battery will drive the motor by a greater current but for a smaller time.

Can you give us a little more information about the battery you intend to remove ? like :
- Capacity in mA.h.
The batt. only states 18vdc. but the trans. is 24vdc. @ 400 ma. and it's for like a trickle recharger for the batt.
 
I'm not that well equiped to have a scope. If I had lab equipment @ my disposal problem would have been long solved...Thanx though!
Ok then -- my suggestion is that you construct a simple (unregulated) PSU capable of at least 5A to Ca. 24V then control same with a variac in the primary circuit --- You will find most of the needed components in an automotive battery charger (in most cases the transformer/rectifier will be of the 'tapped secondary' topology -- hence you may readily derive 28V output via a bridge rectifier arrangement)... Should you experience difficulty locating a variac -- a phase control (e.g. incandescent 'dimmer') may suffice (but you didn't hear it from me!:eek:)

Best regards
HP:)
 

hsazerty2

Joined Sep 25, 2015
32
WELL ! now we are far beyond the initial question which was : is it possible to replace the battery by a capacitor ? the answer is NO.
A capacitor (of a reasonable size) cannot store enough charge and deliver it at a constant voltage like a battery does.

Is your motor still running properly on the battery ? if yes then you probably need a charger of bigger amperage.
 

Thread Starter

Dynamo1

Joined Nov 19, 2015
15
Ok then -- my suggestion is that you construct a simple (unregulated) PSU capable of at least 5A to Ca. 24V then control same with a variac in the primary circuit --- You will find most of the needed components in an automotive battery charger (in most cases the transformer/rectifier will be of the 'tapped secondary' topology -- hence you may readily derive 28V output via a bridge rectifier arrangement)... Should you experience difficulty locating a variac -- a phase control (e.g. incandescent 'dimmer') may suffice (but you didn't hear it from me!:eek:)

Best regards
HP:)
We'll do...I thank you for your efforts and apparent vast knowledge of electronics...This is all groundbreaking to me considering I'm drawing my power from RF energy...GoTo or Google Gerard Morin for details...Thanx again!
 

Roderick Young

Joined Feb 22, 2015
408
The other reason that I can think of to put a capacitor across a DC motor is to supply the surge current for starting torque. The motor usually will draw more current when starting up, and even if the power supply is able to sustain the running motor, it may not be strong enough to sustainstart the motor. One experiment I would do, if I thought it wouldn't hurt anything, would be to start the motor normally with the battery and charger plugged in, then remove the battery, and see if the motor keeps running. If the charger cannot even sustain the motor under those conditions, you will need a stronger charger. If the charger will sustain the motor, then the capacitor idea may help - but 3300 uF may still not be enough to start the motor.
 
Last edited:

Thread Starter

Dynamo1

Joined Nov 19, 2015
15
The other reason that I can think of to put a capacitor across a DC motor is to supply the surge current for starting torque. The motor usually will draw more current when starting up, and even if the power supply is able to sustain the running motor, it may not be strong enough to sustain the motor. One experiment I would do, if I thought it wouldn't hurt anything, would be to start the motor normally with the battery and charger plugged in, then remove the battery, and see if the motor keeps running. If the charger cannot even sustain the motor under those conditions, you will need a stronger charger. If the charger will sustain the motor, then the capacitor idea may help - but 3300 uF may still not be enough to start the motor.
I hear ya...Thanks Roderick...Keith
 
Top