how do I reduce the voltage in a circuit?

[doitmyselfer0523]

Sorry to post such a stupid question, but I was hoping the gurus out there could shed some light on this subject for me.

I have a Garmin navigation system for my car. In the cold weather it fell off of the windshield and landed directly on the power connector. The force of the fall on the power connector broke the power connector on the circuit board. I took it all apart and soldered it back together, but the connection is askew and it doesn’t work unless I physically hold the connector with my hands….

This Garmin device has a battery input in which two AA batteries can power the unit, and this works fine, but I don’t want to keep putting batteries into the unit, I want to use the car-power plug.

So, I soldered the car adapter directly wire directly to the battery input leads. The only problem is that where the batteries provided (2 X 1.5 volts) 3 volts, the car adapter is providing between 5 and 7 volts. The Garmin is not at all happy with the extra voltage at the battery input and doesn’t work.

Yes, I tested the unit back with just batteries to verify that I had not blown up the unit; it still works fine with batteries.

So, I ask a friend of mine how to build something to cut the voltage down to 3 volts. He tells me to use a couple of rechargeable batteries in-line and they would regulate the voltage down. Sounded good to me, so I built the circuit… The positive output of the car charger to the negative battery lead, inline with the second battery, and behold… the voltage was summed, not regulated down. I ended up with 5v + 3V = 8V.

Yes, I am too cheap to purchase another Garmin; the one I have works fine, if I can just feed it the 3 volts it wants. And yes, I am too cheap to go to the auto parts store and purchase one of those multi-voltage output devices. I want to fix this thing and hopefully, you-all are going to help me.

So, my technical cyber friends, what do I have to do to cut the voltage down from 5V (or 7V, I can’t remember) down to 3VDC? Resisters? The worst part is I was an electronics technician in a prior life, but hell if I can remember any of it. I never got to much into power supplies, and if I did I swapped out the whole thing and let someone else back at the depot fix it.

Thanks for your time; please be kind in your replies.

 

[Torben]

What kind of current does the thing draw?


Torben

 

[eblc1388]

The force of the fall on the power connector broke the power connector on the circuit board. I took it all apart and soldered it back together, but the connection is askew and it doesn’t work unless I physically hold the connector with my hands….

The force of the drop had also broken one or more copper traces on the PCB due to bending. These broken traces are very hard to discover normally unless one make a conscious effort to specifically look for them using a magnifying glass.

Luckily they are always around the area of severe damage and in your case around the power connector. Look very carefully at the power connector, unsolder it if need be and look underneath it. The direction of bending on the connector would give some hints to which PCB side the break is on.

Once you have located the break(s), clean both side of the broken trace and bridge them using wire and solder.

Hope this helps.

 

[Hero999]

If you connected the rechargable batteries in series then the votlages would add. Also, this is a bad idea because once they are flat they will start to chage in reverse which could cause them to explode.

If you connected the batteries in parallel and a suitably sized resistor in series then it would work but this isn't recommended as you need to make sure the batteries don't overcharge or go flat.

The best way to get 3V would be to use an LM317 regulator which can be purchased from Maplin electronics in the UK or Radioshack in the US. It just needs a couple of resistors and capacitors to form a regulated power supply.

 

[k7elp60]

So, I soldered the car adapter directly wire directly to the battery input leads. The only problem is that where the batteries provided (2 X 1.5 volts) 3 volts, the car adapter is providing between 5 and 7 volts. The Garmin is not at all happy with the extra voltage at the battery input and doesn’t work.
.

It seems to me, that if you installed a 3.3 volt low dropout regulator between the adaptor and the garmin, such as a LD1086V33 by STM it would solve your problem. The Mouser electronics stock # is 511-LD1086V33.

 

[pfofit]

So, I soldered the car adapter directly wire directly to the battery input leads. The only problem is that where the batteries provided (2 X 1.5 volts) 3 volts, the car adapter is providing between 5 and 7 volts. The Garmin is not at all happy with the extra voltage at the battery input and doesn’t work.

mY bold.

Something is amiss.
If the car adapter is made for the garmin, why is it not happy with the voltage from the adpter?

Are you sure you have the polarity right when you direct soldered?

The higher adapter voltage should drop down under load or the device should have a built in regulator to accommodate the car adapter.

Added: i just reread your statement and noticed this
So, I soldered the car adapter directly wire directly to the battery input leads

You should have solder the adapter wires to where the power input jack is. You may have bypassed the internal regulator of the device by going to the batteries.

cheers