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shobley
06-26-2009, 08:19 AM
I have a new robot with a single 12v lead-acid battery. It's connected via a fuse to the motor controllers and a Mini-ITX board to host the programming.

What are my options if I want to charge the battery? Can I just hook the charger straight to the battery terminals, or should I disconnect the other systems first?

Ideally I want an external charging socket, so that I don't have to take the case off, but I don't really know anything about charging batteries while other systems are connected.

Steve

Adrenalynn
06-26-2009, 11:32 AM
What's the input range on the Mini-ITX's power supply? Remember - you can't charge a 12v battery at 12v...

shobley
06-26-2009, 12:57 PM
I would have to check - the PSU module has been on the shelf for ages - it came from here:

http://www.mini-box.com/s.nl/sc.8/category.13/.f

But I don't see my particular model.

I believe it was a switching model with a fairly wide input tolerance.

I will have to take a look at it when I get home.

shobley
06-26-2009, 04:25 PM
It's a PW 200 M DC-DC power supply. Designed *only* to run at 12v - so not sure if I can charge safely with this connected. Which is a shame.

http://www.mini-box.com/PW-200M-DC-DC-power-supply

I did a quick test with my meter and the 12V output is not a straight pass-thru.

Adrenalynn
06-26-2009, 04:51 PM
Yeah, those are recommended to NOT run from battery. You want the 6v-24v WI (Wide Input) version, which they sell for running Carputers from 12v systems. The version you have requires a regulated 12v brick to deliver constant reliable power.

lnxfergy
06-26-2009, 06:43 PM
Once you sort out your Mini-ITX power supply, if you don't intend for the robot to be on during charging, just have a switch in the line between the battery and the PSU, and have the charger connection on the battery side of the switch.

-Fergs

jes1510
06-27-2009, 11:22 AM
Yep, a DPDT switch will do the job nicely and fixes your problem for around $2.

Adrenalynn
06-27-2009, 11:25 AM
Doesn't change, however, that running that power supply as-is from battery is going to take out the power supply board, the motherboard, or both...

Realistically, it's going to just let the magic smoke go from the regulator itself, but the motherboard may still get shocked.

jes1510
06-27-2009, 11:27 AM
Do'h you are correct. I forgot that a 12 SLA is really over 13V.

Adrenalynn
06-27-2009, 11:55 AM
Probably even worse is when the battery is running flat at 10.8-11.1 and that poor regulator is trying to extract 12v to run stable...

The WI is a step-up/step-down constant power source.

shobley
06-28-2009, 03:04 PM
Darn - well when I bought it I was an electronics doofus.

Now I'm an electronics "knows-enough-to-be-dangerous" :)

So......

If I were to buy a nice wide range PSU unit then I could charge while connected?

Something like this?:

http://www.mini-box.com/PicoPSU-120-WI-25-12-25V-DC-DC-ATX-power-supply?sc=8&category=981

Adrenalynn
06-28-2009, 03:22 PM
I don't see a problem - it's really no different than running a carputer with the alternator shoving charge into the battery all the time. HOWEVER:

That's not a great choice - 12v minimum input means a battery is going to be next to worthless since it will discharge past that quickly.

I'd be looking at something more like: http://www.logicsupply.com/products/m3_atx

Automotive power supplies. (in this case, 6v-24v or better)