Power DC brushed motor with an AC supply

[steelmesh]

Trying to find an inexpensive and simple way to power a DC motor and other 12v controls from a 120v AC power source. The project is refurbishing a robotic scarecrow for a display, it yaws using a brushed DC scooter motor. I am assuming the motor may spike 150 watts at 12 volts.

My idea is to use a computer PSU and parallel this with a 12v SLA AGM 9ah battery. My assumption is the battery will handle current spikes and the PSU will maintain the battery charge (below top voltage of the battery). Is my assumption correct on this PSU/battery thing or am I just an ass?

 

[Modbikemax]

Sounds ok to me. It's pretty much what goes on in a motorcar.
I would use an automatic battery charger suitable for the battery type and big enough to carry the constant current required. Something like CTEK brand chargers.
Sealed batteries cannot vent so to achieve a full charge these chargers do some clever things to get that full charge.
A straight regulated power supply may not achieve full charge unless you risk gassing. Older cars had wet vented batteries and vented hydrogen if overcharged. Grandad would leave the headlights on on long trips to load up the alternator and reduce the volts a bit to stop the battery gassing.
However if you are not worried about getting a full charge a power supply will work just fine just set the voltage at the recommended float charge usually around 13.8VDC, they sometimes print it on the battery.

 

[Matt Gruber]

can use a $2 regulator on the psu and set the voltage just right.
LM2596 ebay it.

 

[Modbikemax]

That just gets you the chip and it's only good for 3amps. You will need a coil cap and schotkey diode too plus a board etc. etc.
For $25 you can get the finished article good for 5 amps.

http://www.ebay.com.au/itm/S-60-12a-Super-Stable-12V-60W-Regulated-Power-Supply-10-5-13-8V-5-AMP-/121237480082?pt=AU_Components&hash=item1c3a512292

 

[Matt Gruber]

http://www.ebay.com/itm/DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Output-1-23V-30V-2014-/301218533352?pt=LH_DefaultDomain_2&hash=item4622060fe8
3 amps is plenty!, plus 20+ amps from the sla!

 

[Modbikemax]

Yes that should work nicely.