car battery power? needs regulating

Hi I'm trying to drive a 9v motor using the car power supply. The plan is to used a 12v to 9v converter such as the one below http://newzealand.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6894781 I understand the outout current from this SIP module needs regulating using a capacitor. My question is whether I'd need to regualate the current going in from the car battery to this SIP. On the same note do I have to regulate the voltage going into relays from the car battery? If so what should I use? thanks!

Save your money - that is not suitable, and to expensive anyhow. (It's a +9V & -9V output with 0V "center" voltage. It only outputs 0.05A = ie, HALF a Watt (into 9V). (Maybe less for motors.) What wattage or current is your motor? You can get 7809 (eg, LM7809) 9V regulators for a few dollars. The common version (TO-220 package) handles 1.0A. Only 3 pins, and for a motor, probably only a diode required... Plus a heatsink depending on total current. Or get the "universal" 317 (eg, LM317T or LM317K) for adjustable output. The 317 requires one 120 Ohm resistor plus another variable (or fixed) resistor to vary (or fix) the output voltage, plus the same "spike" protection diodes (or freewheeling diodes, heatsinking etc.

Hi thanks for the information was looking at the LM7809. Seems the output needs some regulation. Could you explain why a diode would be needed if connecting to a motor? is there a risk of a back flow current? Also would i need to regulate the input current from the car battery going into the LM7809 thanks

The diode is in case of back-EMF caused by the motor - I think the datasheets should provide the info (especially for the 317 which is the same in principle, merely adjustable. From memory it is both reverse spike protection (a reverse biased diode from output to gnd or across the motor +9 & 0V the same as done for relays, AND a diode across the device - ie, biased from output (Anode end) to input (Kathode end), though the latter may be used more for output capacitors. Whether the output needs regulation depends on currents etc, but I doubt a motor will be that fussed. (I was going to suggest a simple resistor to drop the voltage....) No input regulation is required. As long as the max voltage drop (input - output) times the current thru it does NOT exceed its power handling and dissipation capacity (V x Amps = Watts; eg, 15V in, 9V out supplying a 1A motor means it is dropping/dissipating (15-9=) 6V@1A = 6x1 = 6 Watts. The datasheets explains it fairly well - after about the hundredth read! (Mabe.)

Who's Mabe(l)?

Damned cleaner sucked the why right out of my keboard. Sorry - it should be (Maybe.) and keyboard. chaminda, what current is your motor? (Or power @9V etc?) That info will answer many design questions....

Hi I've had a look at the data sheet for LM7809. They just suggest capacitors no mention of diodes. The motor current is around 2a and 9v - a bit difficult to measure as its fixed. http://docs-asia.electrocomponents.com/webdocs/0e1f/0900766b80e1f8e6.pdf

The motor is 2A? Lucky you didn't buy that first regulator then eh? And you'll need the 3A version of the 7809 or 317 - unless you want to add a transistor or two to boost output (eg, 2N3055)?

Hi I think i got it wrong! Couldn't find the exact data sheet for my motor but similar ones only take upto a max of 0.4A. I'll do up a cirucit and post it on here for you guys to check. Think i'll include the capacitors as recommended on the data sheet and some diodes as well thanls

LOL - you & me both! (Misread specs etc..) But that's good - the 7809T should handle it ok. That's the TO-220 package like a big transistor - 3 leads - easy to connect. [Just be careful of the metal tab/tang is usually V-out (eg: 9V).] If cheap enough, buy two - one as spare. Then I wouldn't worry about diodes & caps. The caps are only used when the output varies a lot - and yours doesn't. There might be some ripple, but that shouldn't matter... The 7809 certainly "regulates" better than a resistor which was one option I was thinking of suggesting.... I'll look for more datasheet stuff. It may have been ANs (Application Notes) that had the stuff on added diode protection or inductive loads. (Probably AMs for the LM117/317 or LM150 etc series.) PS - the PSU (Power Supply) may effect input protection - eg, battery ok; if in car - maybe spike protection; if battery charger maybe a cap.