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4mula 04-28-2011 02:53 PM

MPGuino backup power source???
I've done a lot of searching so forgive me if it's already been discussed. I'm wondering if anyone has added a backup power source for their mpguino, like an additional 9v or watch battery for when your car battery dies or connection is lost. Maybe there is even some kind of power reservoir that you can add inline that will store just enough juice. Recently I've lost data a couple times, I may be due for a new car battery, or maybe just doing engine off coasting right before shutting off did it. Even though my car started, it was slow and barely had enough juice so the mpguino restarted. Anyone done it or have any ideas?

Btw on a side note I did add a 5amp fuse inline to protect the mpguino from any surge, is that small enough?

dcb 04-28-2011 03:05 PM

It would be good to know if this is a homebuilt or what?

4mula 04-28-2011 03:16 PM

Oh, sorry, this is the pre-assembled one. Ordered a couple months ago, btw I love it, I can't imagine driving with out it now!

dcb 04-28-2011 04:47 PM

can you try connecting the hookup wire directly to the battery?

bobski 04-28-2011 11:49 PM

If his battery is on its last legs, cranking the starter could be pulling input voltage below the regulator's minimum. That could drag down the voltage to the processor and trip a brownout reset. The MPGuino is set to be more sensitive to that, right?

To answer the original question, yes it's possible to add a backup power source (a 9V might work) as long as you use a pair of appropriately sized diodes to keep the two power sources isolated from each other. Without the diodes, the car would try to charge the 9V, probably destroying it, and the 9V would try (and fail) to power the whole car if the main battery were disconnected.

4mula 05-18-2011 04:52 PM

Yes, it seems the battery is shot. Even though I am planning to replace it I would like to add the 9v. How would I go about doing that? I'm not too hot with electronics . . .but learning (just installed power door lock actuators, relays, and alarm :)
What are diodes and how would I use them?

4mula 05-18-2011 04:53 PM

Oh and yes, I ended up directly wiring the mpguino to the battery (of couse with a small fuse in line too)

bobski 05-18-2011 05:16 PM

Diodes are electrical components that only let electrical current flow in one direction, the way a check valve does for gasses and liquids.

1N4001 rectifier diodes are easy to find (try radio shack) and can handle up to 1 amp of current, which should be fine for the MPGuino.
If you look at the diodes, you'll see one side has a stripe. You want to connect the striped end of two diodes to the positive power supply lead of your MPGuino. The remaining end of one of the diodes goes to the positive terminal of your 9V battery, the other remaining end goes to your car battery positive connection. The negative of your 9V goes to the MPGuino negative (ground) power connection along with the existing car connection.

4mula 05-19-2011 01:00 AM

Thanks so much! Shows how little I know about electronics, probably should have paid more attention in physics II. So I found some 1N4004 diodes on ebay cheap, 12 for $1 shipped from the US.
12pcs 1N4004 rectifier diodes 1amp upgrade for 1n4001 | eBay
I'm sure that's cheaper than radio shack, plus I'm saving gas by not having to drive anywhere :D :D :D
Will these work? Sounds like they are basically 4 times stronger

bobski 05-19-2011 02:05 AM

Yeah, the higher numbered 1N400x diodes just have higher reverse voltage tolerance IIRC. A higher than needed spec won't hurt anything but your wallet.

That price is fine if it's all you need. If you were buying other components, or a large quantity of diodes, you can get them from the major parts suppliers for a fair bit cheaper: link. The issue is the cost of shipping.

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