power for stamp and HB-25 Motor Controller

dwbowen

Hello All,

I am writing to see if it is possible to run a bs2 and three HB-25 Motor Controllers off the same power source? I am using 3, 12vdc 5 amp lead acid batteries wired in parallel. Is there an adapter that will reduce the voltage enough to run a bs2 homework board without smoking it? I do not want to have a separate battery for the controller because I would like to be able to recharge using a single charger. I attempted to hack a 12vdc to 5vdc car cigarette lighter adapter to reduce the voltage but when connected my motors did not function. The Stamp got power and the HB-25's green lights where on but when I sent the pulsout command to the stamp the motors did not work. Any ideas???

cheers!

david bowen

Mike Green

1) When you have more than one power supply, you have to connect the grounds together. Your 12V to 5V adapter probably did that anyway, but things won't work if the grounds are not in common.

2) A BS2 will run on 12V, but the regulator on the Stamp module (and on the development boards) doesn't have a heatsink adequate for significant current loads at that voltage. You can buy LM7808 linear regulators from a variety of sources that will drop the 12V to 8V which is well within the normal range of power supply voltage for the BS2. You'll need a capacitor on the input side of the regulator. See the datasheets for the regulator for details. Usually 0.1uF is a minimum for the LM78xx series.

Bill Chennault

David--

I am using two, 12 amp hour lead acid batteries wired in parallel for a total of 24 amp hours. Additionally, for Stamp power (five of them), I use two 7.2 volt, 4200 maH batteries wired in parallel for a total of 8400 maH. I have run the Stamps for WEEKS on this system without problem. Thanks to a suggestion by Mike G., I have a Futurlec solid state relay controlled by one of the Stamps that shuts the 12vdc system down and brings it back up when needed.

I do not know how long I COULD run the five Stamps on the 8400 maH system. Maybe much longer than I have to date.·The problem of using two charging systems pretty much disappears in a setup like mine, but I certainly understand your point.

I have several hours on the 12vdc system and have NEVER recharged it. Right now it is providing 12.86 volts to my gear motors.

--Bill

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You are what you write.

Chris Savage

David,

The HB-25 should be powered up after the controller, even if using the same power supply. Ideally you’d want a separate power supply. Take care.

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Chris Savage
Parallax Tech Support

dwbowen

Hi Chris,

Thanks for the advise. I will use separate power supplies... But in order to use just one power switch and program in the delay needed for the HB-25s would it be possible to use a relay connected to the stamp to power up the HB-25s? If so do you or does anyone have any recommendation on what relay might work for this purpose?

cheers!

Bill Chennault

dwbowen--

I ran into exactly the same problem as you: Where could I find a relay that would handle the current I needed for my seperate 12 volt system? (My system, on Ugly Buster, consists of 8400 maH of 7.2v logic power and 24 aH of 12v gear motor and everything else power.) Thanks to Mike Green, who pointed me at the 40 amp Futurlec SSR (solid state relay, part number SSRDC100V40A; use that number as the search criteria at the Futurlec site), one of my Stamps now powers the 12 volt system up and down programmatically. The code is dirt simple, as is the Futurlec SSR.

I am very happy with this arrangement.

--Bill

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You are what you write.