12 VOLT SOLAR CELLS, AND DYNAMO CHARGER ??????????????

Good Evening,

I'm building a 12 volt recharging system with a 12 volt, 0.375A (12"x12") solar cell, and this charge controller:

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The battery is a 12 volt NiMH, 3AH.

I would also like to be able to use a hank-cranked dynamo charger, and also a way to recharge the battery using regular 120 AC mains. The dynamo that i wish to use comes from a very cheap survival radio, that uses

3.6 volt NiMH, but i think there are Zener diodes that limit the voltage coming from the generator to 7-8 volts, so i think i can remove these to get more voltage (closer to 13-14 volts?).

I believe i could just use a regular 13.8 volt DC power supply, and have a 3-way switch to go from the solar cell, to the dynamo, or to the AC power supply, directly to the charge controller above. I other words, the charge controller (made for photovoltaics) would be used for any of the three sources of DC power.

Does this sound like a good idea? Or should i get a separate charger for the DC power supply?

Is there a cheap, simple LED circuit that can indicate the charging function and the state of the battery?

Thanks for your help,

Slick

Reply to
Dr. Slick
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Best check that charge controller is designed to work with NiMH cells. They behave differently to Lead Acid cells.

Might work but I suspect you may have to turn the dynamo 3 or 4 times faster (12/3.6 = 3.333 times). This might not be possible without changing the gearing? At that voltage/rpm the dynamo may not be very efficient.

You need to find out more info. Ask the makers if it's possible to power the charge controller fro a DC source and what input voltage range is required to charge 10 NiMH cells.

Reply to
CWatters

On 10 Oct 2004 08:16:11 -0700, snipped-for-privacy@aol.com (Dr. Slick) wroth:

You don't need a charge controller for the solar cell source. Its output is 1/10th of the battery's capacity and that amount of charge current will be fine with no controller in the system.

You don't need a charge controller with the dynamo either.

If you use a "normal" commercial battery charger for the 120 volt AC source, you won't need a seperate controller either.

A simple voltmeter will give you all the information you need to determine the health of the battery.

Jim

Reply to
James Meyer

current

The 1/10th overcharge rate is usually ok (in that the battery won't over heat or explode) but it might shorten the life of the battery if used long term. Manufacturers recommend a lower rate if you are planning to leave the battery on float for very long periods.

eg cells that exhibit a higher than normal "on charge" voltage are less healthy.... or did you mean you can use a volt meter as a charge state indicator? That's only possible if you calibrate it carefully :-)

Reply to
CWatters

Hi Dr. Slick,

Look into real alternators for motorcycles or cars. These are usually much better quality and longer lasting. And cheap. Better bearings, too.

Regards, Joerg

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Reply to
Joerg

The charger you are going to use is not designed for a NiMH (they dont say, but I am sure it is a lead-acid type). Refer to a NiMH manual before you go ahead with this. Otherwise be aware that the battey might catch fire.

Reply to
Tom Seim

On Sun, 10 Oct 2004 20:24:57 GMT, "CWatters" wroth:

Solar cells will only provide current when the sun's shining. That reduces the total current available over the long term to a value that should be safe. Not to mention that most solar cell manufacturers rate their cells for a perfectly clear day on top of Mt. Everest during a solar flare. 8-)

I meant that if one weren't going to automate the process or attempt to provide legally binding measurements, that a quick look at the voltmeter would provide all the information one should need to determine the condition of the battery. Of course the voltage would be different depending on the load and the temperature and whether the current was going into or out of the battery.

Jim

Reply to
James Meyer

and when the planet is closest to the sun

mike

Reply to
m II

You may be right, as the batteries they sell seem to be lead acid.

I was also looking at this charge controller:

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It seems a bit simple, but it may be good enough for what we need. It says it can take NiMH too.

Slick

Reply to
Dr. Slick

too.

An alternator for an automobile, and probably a motorcycle also, are way too much for a charger that needs only a half amp. Cars use a hundred times that current.

I've used a hard disk spindle motor to drive some LEDs. Try it sometime. It depends on the motor, obviously it has to have permanent magnets.

Reply to
Watson A.Name - "Watt Sun, th

Hi Watson A.Name,

The one I saw in a friend's scooter was just the size of a fist. After all, you need some mass and size if you want to operate it with a hand. Either the other hand needs to grab it or it would have to be mounted on something. There should also be suitable versions for riding lawn mowers and stuff like that.

I have to try that. Wish I had kept the last HD that had croaked.

Regards, Joerg

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Reply to
Joerg

To safely charge NiMH you must sense & terminate charging on either:

  1. dV/dt drop
  2. dT/dt drop This circuit doesn't seem to do either. Check out:
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Tom

Reply to
Tom Seim

Newer NIMH's, like the C type cells from Sanyo, can take long term overcharge without problems. Check your data sheets.

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KC6ETE  Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
Reply to
Dave VanHorn

I became interested in solar energy recently.

Looking at some of the circuits on people's websites, they do seem rather amateur.

Often it is just a few solar cells and a diode into a NiCd/NiMH battery. Which will work but very crudely.

The Art of Electronics has some excellent introductory text on batteries and solar cells.

It notes that Lead-acid cells are best suited to the natural power curve of solar cells.

I get the feeling they are more robust against overcharging and overvoltage than other chemistries. They certainly seem okay with the simple charging circuits in most cars and chargers.

The British Antarctic Survey use lead-acid in their polar instrumentation. Now there's an extreme application. Like Dr. Slick's app, they use turbines and solar cells, but of course they have to work for several years unattended. Cells have to harvest sun over a six month summer, as there is none during the winter.

Dr. Slick, what is your application? i.e. what is the power to be used for?

Reply to
Kryten

Do you have to worry about Low Voltage disconnect with NiMH? With lead-acid, you obviously do...

S.

Reply to
Dr. Slick

This will power two 40-60 watt lights, with a motion detector attached.

Are lead-acid batteries really the way to go? Some charge regulators don't have a low voltage disconnect circuits, so the battery can be drained if you aren't careful. If i'm not mistaken, NiMH don't have this problem, right?

Slick

Reply to
Dr. Slick

More info please.

Are these lights going to be moved around much, or stay put?

If they are for camping expeditions, nickel cells are going to be less mass to haul up hills. If you take a camper van, then weight isn't so important. If it lights up an isolated survival hut, it isn't very important at all.

Depends how they are being used.

All cell chemistries have their own care requirements.

See

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Most people just see them as things you charge up and use, like a fuel tank. It usually doesn't matter if mistreated cells wear out earlier, if a MP3 player runs out at an inconvenient time. You can pop into a store and get some new ones (and send old to recyclers).

If your cells are in a radio repeater in the desert, a fortnight camel journey away, then one should make sure the cells are managed as best as possible. This example just avoids tedious trips. If your cells are in a survival shelter, it could save lives.

I bough some solar garden lamps out of curiosity. The instructions recommend changing the two AA nickel cells every year.

IIRC no cells like being drained as flat as a witch's tit.

How likely is this going to be?

If it is motion detector driven, it would need something moving for a long time.

Your battery is 36 WHr energy, so 2x50W would drain it in 0.36 Hrs.

I have a mental image of some mischievous Gary Larson bears investigating your lamps on a woodland cabin.

They can do so for 21.6 minutes, at night.

Which reminds me you could do with a sensor to disable the lights during the day, so passing bears don't waste the battery energy.

BTW I can send you a copy of the solar cell pages from the A of E.

K.

Reply to
Kryten

Well, I did that. From Sanyo's manual

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"Also, to obtain a long service life from the Twicell, over-charging must be avoided as much as possible."

This assertion that over-charging is ok comes up time and again. Yeah, it's ok if you don't care about battery life.

Tom

Reply to
Tom Seim

In article , Kryten wrote: [...]

IIRC the Silver Chloride (or something like that) battery loved being discharged. You had to discharge it for storage. You could charge it up, use it for a day and then run it flat. Discharged it would last for years.

The down sides were: Charged it went bad in a month and they cost a *LOT* to replace. The only Silver Chloride batteries still in use that I know of are the ones for testing blasting caps.

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kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

NiCD cells DO like to be drained completely flat.

Otherwise you get the old memory effect if you try to recharge them when they are only partially discharged, and the cells will then not hold a full charge.

Slick

Reply to
Dr. Slick

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