Power Adapter Advice

[peterclones]

Once I complete my project I'll need a 5V or 6V 3A power adapter for the 08M servo driver kit. I have an old laptop power adapter from 7 or 8 years ago rated for 19V and 3.3 Amps. Would this thing be regulated power, and what would be the best way to bring it down to 5V or 6V?

I'm also considering this adapter from Pololu, which apparently is a "switching power adapter regulated at 5V" according to Pololu's site:
http://www.robotshop.com/ca/5vdc-3a-wall-adapter-power-supply-2.html

Or this one from Lynxmotion, but it's $20 more for some reason:
http://www.robotshop.com/ca/6v-wall-adapter-2.html

Thanks.
Pete

 

[premelec]

Unless you want to use a linear regulator with a large heat sink for the 19v supply [60 watt] you'd need to find a switching down regulator module to drop the 19 volts efficiently - and it's a lot more power than you need. On the other options the less expensive one says 3 amp max... do you really need 3 amp?
Is your peak current higher? There are so many power supplies around your might even find something in a local computer repair or thrift store to suit you - and remember if you have high current devices operating near or on same supply as PICAXEs you may have trouble with spikes - be sure to have adequate bypassing and ground V-s tied properly.

 

[peterclones]

I'm running 3 servos that can operate at 750mA or more under load, so I'm told. So I figure I need 3 amps or so peak. Likely won't ever exceed that. The manual for the 08m servo kit mentions adding more capacitors but I don't know exactly where and which kind/size. Any advice on that if it becomes necessary?

 

[westaust55]

While I do know how to open the welded/glued moulded plastic type cases on many power supplies and the like, for a laptop switchmode PSU you are unlikely to find a schematic and thus how to modify it internally for 5V dc output. Therefore you have two options:
1. a separate 19 V to 5 V supply
2. a new mains to 5 V dc supply.

Here in Aaustralia you can buy a universal 100-240 Vac (50/60Hz) to 5 Vdc 3 Amp output switchmode power supply for AUD$22.
http://www.jaycar.com.au/productView.asp?ID=MP3480&form=CAT2&SUBCATID=1000#12

I have used several of these SMPS myself.

 

[srnet]

You could use the Laptop supply.

A 5A adjustable step down regulator module will cost you around £3 delivered off eBay.

 

[geoff07]

Or an old mobile phone SMPS as it is. If it is very light in weight then that is what it will be. Better not to use the heavy ones with a 50Hz transformer as they waste much more power.

 

[SAborn]

If you really want to use the laptop supply, one option would be to use a separate linear voltage reg (LM7806) for each servo and a 5v reg (LM7805) for the picaxe, that way the current through each reg is reduced along with the temperature, and far easier than trying to drop 19v to 6v at 3.3 amp.
Each Vreg and handle a startup current of 1 amp, also can be mounted to a common heatsink.

It will mean 4 Vregs, and proberly not the best solution, but it will work just the same.

 

[hippy]

I have a 12V to 6V converter for an old camera using a 7805. Dropping 6V at 1A causes the heatsink to quickly become a highly efficient hand toaster and it shuts down with thermal cut-out after a short while. Dropping 13V at 3A would probably require a lot of heatsinking.

 

[SteveT]

This project of yours is for a 3 servo biped robot correct?

Why are you looking at mains derived power supplies? Surely you would be better of with a 3s LiPo abd a 5A UBEC???

 

[peterclones]

Thanks guys. I think I'll just look for another supply then. Seems like the easiest solution. This is for a stationary robot arm type of thing, not a biped robot.

 

[noelnelson]

If you are not worried about compactness, get hold of an old desktop pc power supply. Google ATX power supply.
These have multiple 12V and 5V outputs, well regulated and with plenty of power capability.
(You will have to connect the +5V standby to a +5v output to make it start up)

 

[inglewoodpete]

I bought several of these LM2596-based switchmode regulator boards from Deal Extreme a while ago. They're compact, efficient and have mounting holes (some designs don't!).