How does a battery charger work?

[Guest tak1]

I have some plans to make an external power pack for my 315 but I need to know how a battery charger works. The one in question is a 14.4 volt charger for a drill/sabre saw.

 

tak1

[Guest CharlieP]

Considering that you are asking this question, you may want to rethink the power supply, you could damage the GPS beyond repair with an over-voltage. I would recommend multiple sets of rechargeable NiMH batteries for your GPS instead. But to answer your question, the typical battery charger is a transformer which reduces 120 volt AC to an appropriate DC voltage in order to push a reverse current through the batteries and recharge them. The quality of the DC current may vary, and may not be filtered at all, i.e. it may cycle at 120 times a second from zero to the charge voltage (rectified sine wave). Therefore, applying this output to an electronic device which is designed for a flat voltage, even if the voltage is right, could still zap the devices IC's.

 

FWIW,

CharlieP

[Guest CharlieP]

Considering that you are asking this question, you may want to rethink the power supply, you could damage the GPS beyond repair with an over-voltage. I would recommend multiple sets of rechargeable NiMH batteries for your GPS instead. But to answer your question, the typical battery charger is a transformer which reduces 120 volt AC to an appropriate DC voltage in order to push a reverse current through the batteries and recharge them. The quality of the DC current may vary, and may not be filtered at all, i.e. it may cycle at 120 times a second from zero to the charge voltage (rectified sine wave). Therefore, applying this output to an electronic device which is designed for a flat voltage, even if the voltage is right, could still zap the devices IC's.

 

FWIW,

CharlieP

[Guest tak1]

MH batteries for your GPS instead.

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Actually this is what I want to do. If you have ever deconstructed a battery from a drill or other cordless device, you will likely find that it is made up of multiple cells wired together in series. The battery pack in question is made up of 12 cells, each cell putting out 1.2 V (plus or minus a little). So if I wire them together correctly I can multiply battery operating time by a factor of 4 (I'll let you figure that out for yourself). So I was considering how I was going to go about charging them once they are drained and that is why I needed to know how a charger works.

 

tak1

[Guest mcb]

I looked at the manual for the 315/320 on Magellans web site and it says that the GPS can take 9-16 VDC through the power power port. Why not just hook the 14.4 VDC from you cordless drill battery directly up to the GPS through the exteranal power plug. Then you don't need to modify or get a new charge if you don't change the output voltage of the battery pack.

 

If you do however change the packs voltage by reconfiguring the cells inside then you can look up on the internet voltages and currents needed to charge a paticular type of battery. The slower you charge a battery the better on the battery but we all know time is money. But slow charging is the simplest and easiest way to charge a battery. If you want to go faster then you need to change voltages and current as you go. Not an easy thing to do. You also have to be carefull with over charging a battery. Lead acid don't care much but other types can be damage if you over charge them.

 

Later

mcb

[Guest phantom4099]

I see some places like cabelas sells 12 volt power packs with a cigarit lighter adaptor. I myself bought a 12 volt game feeder battery, cigaret lighter adaptor, and a small bag to carry the GPS, maps, software and battery charger. This gives me enough power to run my merigold for several day (even with the backlight on full). I once took it on a 1600 mile road trip to ney york city and stayed there for a week and one charge lasted me the whole time with the GPS constantly on the whole time I was moving. My method may not be the best for hiking (the battery is a big one) but some of the smaller ones that cabelas has are pretty small and can fit on a belt loop.

 

Wyatt W

[Guest JollyBGood]

Hey this thread got me thinking about something I stumbled across a while back. It may be just the ticket!!!

 

Check out the following link. I'm thinking of ordering one as we speak.

 

http://www.baproducts.com/rpsl-600.htm

 

Jolly Blackburn

[Guest JollyBGood]

This site has the same product for sale as well as a competing brand. Has a bit more info and images on exactly how they work.

 

http://www.outdoor-catalog.com/power/12_volt_rechargable.htm

 

at 4 and a half pounds it may be a bit too heavy to take geo caching (though with the should strap I guess it's really not that bad if you're going on a mega-hike into the boondocks). But it would be perfect for keeping a good steady source of power to your GPS while downloading maps from your PC. I have a MAC running virtual pc and it takes as long as three hours sometimes to download 24 megs of maps into my Vista. Very frustrating when the batteries give out before the download is complete. This may be what I've been looking for. As a bonus with the surge protetion/fuse I suppose I could plug my auto adapter for my laptop into it and run it for 23 hours on battery power instead of 4 hours.

[Guest JollyBGood]

Aaaaah, should have known Radio Shack would have the simplest solution. For 11.95 you can buy an AC converter which plugs in the wall and has a ciggarette lighter socket.

 

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=22%2D501

[Guest tak1]

One reason that I don't want to use the power converter (cigarrette adapter) is that I have been informed previously that the process that takes 12 V and steps it down to 3.8 V is very inefficient, thus negating the advantage to haveing a bigger battery.

 

tak1

[Guest CharlieP]

quote:

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Originally posted by tak1:

One reason that I don't want to use the power converter (cigarrette adapter) is that I have been informed previously that the process that takes 12 V and steps it down to 3.8 V is very inefficient, thus negating the advantage to haveing a bigger battery.

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That may be true where a resistor is used to lower the voltage, but some GPS units will make efficient use of the higher voltage. My Apelco GPS11 (rare old GPSR) will draw only half as much current from a 12 volt input as it does from the 6 volts from 4 AA batteries, so it gets the same power from the higher voltage with a lower current. Maybe someone out there knows if that is true for the Magellan units. BTW, you can buy 4 AA NiMH batteries and a small 10 hour charger for US$15 at either Ritz Camera or MicroCenter.

 

FWIW,

CharlieP

[Guest mcb]

There is no advantage to dissasembling the batter and giving the unit a lower voltage.

 

mcb

[Guest tak1]

mcb

 

Which part of the manual states this. I just about have it memorized and I haven't seen this.

 

tak1

[Guest mcb]

tak1

 

I looked in the pdf version of the manual for the 315/320 I downloaded off of Magellan's website. Look on page 59 of the manual (the PDF viewer says 67 of 78). This is the specifications page and it says near the bottom under the power/source heading that "2 AA alkaline or lithium batteries or 9-16 VDC with power cable" This makes me pretty sure that you could feed it that 14.4 VDC battery directly if you hooked it up through the power cable hook up. DO NOT connect this directly to the battery terminals inside the unit. You will probably let the magic smoke out. Think about it; if you hook up your GPS to your car with a cigarette light adapter you can buy for the 315 then you are feeding it 13.7 VDC off the alternator in you car. I don't think that has any type of power regulator in it other then a 1-2 AMP fuse. Others should be able to verify this for you.

 

mcb