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Old 05-13-08, 06:51 PM   #1
Air
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Batteries: Replace or Recharge

So I run my gps pretty much every ride. Along with a Cateye in front and a blinkie in the back I'm noticing that I've gone through a bit of batteries. I was thinking of getting a charger and running rechargable batteries instead but was wondering if the charge won't last as long (so instead of the gps lasting 25 hours would it last 20 or 15 instead).

Thoughts?
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Old 05-13-08, 07:54 PM   #2
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Which GPS? Is it rechargeable via a USB computer connection in addition to disposable batteries?
It's relativity easy to recharge Ni-MH batteries as you pedal along by using a dynamo. All you do is use a bridge rectifier circuit to convert AC made by the dynamo to DC for the batteries. Ni-MH batteries will regulate the voltage of the dynamo automatically. As voltage approaches the Ni-MH batteries rated recharging voltage internal impedance created by the batteries will prevent the dynamo from being able to produce more voltage than the batteries can stand. This allows from between 2 to 5 1.2-volt rechargeable batteries to be connected to the bridge rectifier and recharged as you pedal along. You can have one set of batteries in the GPS unit while the second set is being recharged. You will need to calculate how much time it will take to recharge your batteries. This information is located on the batteries. Nearly all dynamos provide 500mA which just happens to be the suggested rapid recharge rate for Ni-MH batteries. After you figure out how long to recharge the batteries simply reset the trip time on your cycle computer which will start and stop as you do and when it reads the time required to recharge your batteries just disengage the dynamo. Here is a photo of a bridge rectifier using 1N5818 diodes soldered to a terminal strip.

The yellow wire attaches to the dynamo and the other dynamo connection is grounded to the frame of the bicycle via the mounting tab. DC output is via the red positive and black negative wires. There is no need to water proof as it's a solid state device immune to fresh water.
Here is the circuit I use to recharge my GPS unit or a cell phone via a USB connector.


I am adding a better pic of the bridge rectifier to make it easier to copy.

Last edited by n4zou; 05-13-08 at 08:25 PM.
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Old 05-13-08, 08:27 PM   #3
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Well i take it we're talking about "AA" batteries here. Alkaline disposables tend to have more "thereoretical" capacity (ie high Ah rating) than NimH. However, NimH can sustain current drain better than Alkaline and may in actuality last longer. It all depends on your equipment. Oh and temperature, NimH is much better in colder temperatures.

If you're burning through allot of batteries i would go rechargable, you'll see the cost savings fairly quickly.
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Old 05-13-08, 09:06 PM   #4
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Quote:
Originally Posted by n4zou View Post
Which GPS? Is it rechargeable via a USB computer connection in addition to disposable batteries?
It's relativity easy to recharge Ni-MH batteries as you pedal along by using a dynamo. All you do is use a bridge rectifier circuit to convert AC made by the dynamo to DC for the batteries. Ni-MH batteries will regulate the voltage of the dynamo automatically. As voltage approaches the Ni-MH batteries rated recharging voltage internal impedance created by the batteries will prevent the dynamo from being able to produce more voltage than the batteries can stand. This allows from between 2 to 5 1.2-volt rechargeable batteries to be connected to the bridge rectifier and recharged as you pedal along. You can have one set of batteries in the GPS unit while the second set is being recharged. You will need to calculate how much time it will take to recharge your batteries. This information is located on the batteries. Nearly all dynamos provide 500mA which just happens to be the suggested rapid recharge rate for Ni-MH batteries. After you figure out how long to recharge the batteries simply reset the trip time on your cycle computer which will start and stop as you do and when it reads the time required to recharge your batteries just disengage the dynamo.
Wow - that's pretty awesome!

I have Garmin Vista HCx - I don't think it can be charged directly but I have plenty of battery packs laying around where that setup would work. I was thinking pretty short term but this is an awesome setup and appeals to my inner geek Thanks for writing it up!
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Old 05-13-08, 09:13 PM   #5
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Originally Posted by Pig_Chaser View Post
Well i take it we're talking about "AA" batteries here. Alkaline disposables tend to have more "thereoretical" capacity (ie high Ah rating) than NimH. However, NimH can sustain current drain better than Alkaline and may in actuality last longer. It all depends on your equipment. Oh and temperature, NimH is much better in colder temperatures.

If you're burning through allot of batteries i would go rechargable, you'll see the cost savings fairly quickly.
Yeah - my fault for not putting in the AA, sorry! That's interesting about colder weather - good to know.

Suggestions as to good prices for charger and batteries?
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Old 05-14-08, 08:42 AM   #6
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Quote:
Originally Posted by Air View Post
Yeah - my fault for not putting in the AA, sorry! That's interesting about colder weather - good to know.

Suggestions as to good prices for charger and batteries?
This battery and charger combo will work just fine as will other battery and charger combos.



I like overnight slow chargers as there is no way you can damage the batteries by overcharging. Four batteries allow you to install two in the GPS unit and two in a small plastic container when you need them.
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Old 05-14-08, 09:23 AM   #7
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I would suggest that you search for something like this. SANYO ENELOOP AA 2000 MAH 4 BATTERY PACK IN SANYO CASE
ULTRA LOW DISCHARGE NIMH
They don't discharge like most NIMH, not as much power, but retaining the charge more than makes up for it, IMHO.

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Old 05-14-08, 01:21 PM   #8
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Yeah +1 on the Enveloop batteries.

Also, look at the LaCrosse BC-900 charger. Very optimal design, makes sure that each and every battery gets topped off all the way up individually instead of just batching them. It'll make your batteries last longer.

Last edited by wirehead; 05-14-08 at 01:22 PM. Reason: forgot to complete sentence
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Old 05-14-08, 02:35 PM   #9
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I've got a boatload of batteries and a GPSMAP 76S, which is similar, just higher drain than the OP's Vista. My two main sets of batteries are powerex 2700's and Eneloop 2000's. For just about everything, the Eneloop ends up being the better battery except things like my GPS.

The Eneloops seem to run at a slightly lower voltage, kicking out low battery warnings way too early, plus the obvious fact it has significantly less total capacity. If you're used to swapping batteries at least once every two weeks anyway, the higher capacity Sanyo or Powerex 2700's are going to be better for the GPS than Eneloops. Same for primary lighting. For blinkies, TV remotes, wireless keyboards and mice, etc. the Eneloops are the way to go. GPS & primary lighting, the higher cap cells are better IMHO.
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