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Author Topic: Charging a 6 volt off grid?  (Read 5056 times)

xyzer

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Charging a 6 volt off grid?
« on: April 20, 2016, 12:32:46 AM »
I have an off grid place with 12 volt solar + diesel generator. I also have a tractor there that has a 6 volt system and I want to keep the battery in a fresh ready for business state. Having the odd voltage around makes it hard to do this. A small solar system will do but finding a small but not to small panel is difficult. My question is would putting a 1.5 watt 12 volt panel cause the battery harm. I have a friend that does this with his and it seems to do fine. A suggestions appreciated!
Dave
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Tom

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Re: Charging a 6 volt off grid?
« Reply #1 on: April 20, 2016, 12:47:45 AM »
If I may make a suggestion, convert the tractor to 12v and put an orbital battery like an Optima in it. The orbital battery chemistry has a much, much lower self discharge rate, so you can come back after 9 months and it will crank right up. The 6v starter will do just fine on 12v, unless you're cranking it really hard for a long time. A charging system to keep a FLA battery at a good state of charge will eventually boil the water out of it causing the dead battery issue you're trying to prevent in the first place.
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dieselgman

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Re: Charging a 6 volt off grid?
« Reply #2 on: April 20, 2016, 02:00:02 AM »
We sometimes used 6-volt starters with 12-volt batteries in older VWs. They would do just fine as long as we swapped the 6-volt solenoids for 12-volt versions. Many starters have common parts like this readily available. The motors would crank at a faster rate, but I don't believe we experienced any motor failures with this setup even after extended periods. Of course the battery charging systems had to be updated to 12-volt... another easy swap of parts would suffice.

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Thob

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Re: Charging a 6 volt off grid?
« Reply #3 on: April 20, 2016, 02:53:07 AM »
I have a 9n Ford that was 6 volt and I put a 12 volt battery in it.  I changed the starter relay to 12V (no solenoid).  I changed out the generator for a 12V alternator (bought a kit including alternator, proper pulley, bracket, etc.)  At first, I added a resistor in the ignition but it needed a new set of points every year.  So finally I updated it to a 12v coil and electronic ignition.  It has been working this way for several years now.

That's a lot of work and fair bit of change, so to answer your original question, yes you could put a small 12v solar panel on it.  They typically only put out a fraction of an amp, and will work just fine at 6V.  I don't have a good answer as to how long your battery will last, my experience with batteries has been all over the map.  But it works for your friend, it should work for you as well.

There are also some simple charge regulator circuits that could be built with an LM317 and a few components.  I think there's one in the LM317 datasheet, I don't know if you're into building your own or not.  It could be powered from its own solar panel or powered off of your existing 12v system.
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mike90045

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Re: Charging a 6 volt off grid?
« Reply #4 on: April 20, 2016, 05:48:57 AM »
... would putting a 1.5 watt 12 volt panel cause the 6v battery harm.....

Not likely. 
A 12v 1.5V panel can deliver 15V @ 0.1A (100ma)  (W / V = A)   [A 12V battery needs 15V to charge, typical "12" v panels are close to 15-18V]

A 6V 80Ah battery [ my guess at a smallish tractor battery ]  could easily absorb 100ma of "trickle charge" for months.  You would have to check water
levels and likely add distilled every other month to top it off.    PV panels are current sources, and attaching a 12v panel to a 6v battery just wastes half the power
and is unlikely to overcharge the battery

BruceM

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Re: Charging a 6 volt off grid?
« Reply #5 on: April 20, 2016, 06:19:35 AM »
You should be OK if the 12V nominal panel is small enough current.  (<100ma) The upside is you get to use very small wire, since can afford LOTS of voltage drop.

You could play it safe and use a fixed 7V regulator like: BA17807T-ND at Digikey.  It will need a heatsink because of all the voltage drop.

On some panels you could drop the voltage by shorting the bypass diode on the back of the panel.  Or you could just cover some cells.




LowGear

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Re: Charging a 6 volt off grid?
« Reply #6 on: April 20, 2016, 07:17:50 PM »
How about one of those $25 solar trickle units from eBay or Amazon?  A small resister or 50 feet of line spliced in might be needed to drop that 14 or so volts down to 7 or 8.  Or shade part of the panel?  This is to just keep the 6 volt battery topped up - right?

I'd probably just stick a 12 volt battery in there as suggested above only just wait and see what happens down the road.  Yeah, my folks were hill-folk.

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broncodriver99

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Re: Charging a 6 volt off grid?
« Reply #7 on: April 20, 2016, 07:50:15 PM »
Why not just pick up a 6v solar panel?

BruceM

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Re: Charging a 6 volt off grid?
« Reply #8 on: April 20, 2016, 08:07:22 PM »
Here's a cheap 6v PV regulator:
http://www.amazon.com/Controller-Battery-Charge-Regulator-Intelligent/dp/B0191QN8RA/ref=sr_1_1?ie=UTF8&qid=1461178626&sr=8-1&keywords=6v+solar+panel+regulator 

Might work fine on your 12v panel, though they do have some small (half amp) 6V panels at amazon also. 

http://www.amazon.com/gp/product/B0091PU5TG/ref=s9_simh_gw_g107_i1_r?ie=UTF8&fpl=fresh&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-1&pf_rd_r=0RT5GVHSE7PTVJC8R3WJ&pf_rd_t=36701&pf_rd_p=2437869742&pf_rd_i=desktop

Bit of a rip off for just 3.5 watts!  Some foil tape on a 12v panel might be cheaper.  Test with post it notes.

Some of the best bargains on solar panels are at Solarblvd.com.  Some of the non big brand panels may not meet the marketing spec for output. Be prepared to test if you really need full capacity. 

xyzer

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Re: Charging a 6 volt off grid?
« Reply #9 on: April 20, 2016, 10:09:02 PM »
Bruce, and all
Good find on the 6v panel! I am going to use a 12volt and some tape to back it off a bit. Changing over the tractor to 12 volt is a bit more than I want to deal with. I just bought a new 6 volt battery so I'm going to put a small 12volt on it and cover a bit of it.
Thanks again!
Dave
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glort

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Re: Charging a 6 volt off grid?
« Reply #10 on: April 21, 2016, 03:24:16 AM »

There are also some simple charge regulator circuits that could be built with an LM317 and a few components.  I think there's one in the LM317 datasheet, I don't know if you're into building your own or not.  It could be powered from its own solar panel or powered off of your existing 12v system.

That would be my suggestion as well. I am a rank amateur at electronics but you can make things up from these from Data sheets and figure the rest out. I did make up a voltage drop config years ago with these.  I wanted to drop a 12V battery to 9V for a flashgun. I needed plenty of amps so I ganged the things up on a heat sink. It would get pretty warm but it worked.

The other thing that could be dead simple with this is to use a resistor on the 12V.  The internal resistance of the battery will let the thing pull down the voltage if the power is low enough. You are not going to need much with this, just enough to combat the self discharge of the battery itself.  A resistor is basically a light bulb. I'd try and find something like one of those push in pigtail lights like used in dashboards that are 1 or 2 W and put that in the feed line.  With the low power it will pass ( 1-2W as the rating of the bulb) the battery will pull it down to the float voltage and that will be it.  The bulb will take up the resistance and you'll see it glowing brighter or darker depending on what the state of the battery is.  Bright will be charging, dim will be when the battery is charged.

I would get a low watt bulb, connect it up and just keep an eye on the battery voltage and work it from there. If the voltage is too high, add another globe in series which will pull the power down some more.  Also you would want to do this after the tractor has been run and wait a few days before going to a higher wattage bulb. at that charge rate, it could easily take days for the battery charge to level out.
Light bulbs are the simplest and cheapest way of doing this I can think of.

Remember with whatever you do, for a 6V battery, you don't want 6V, you'll be needing around 7.2.  At 6V, a 6V battery is pretty discharged.

Quinnf

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Re: Charging a 6 volt off grid?
« Reply #11 on: April 22, 2016, 05:15:30 AM »
Back in my ham radio days, we used to charge 12V Ni-Cd battery packs for our portable radios using a #53 light bulb run off a 12V car electrical system as a mobile charger.  Worked great.  Current tapered off to zero as the battery pack came up to charge, and the light would go out. 

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EdDee

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Re: Charging a 6 volt off grid?
« Reply #12 on: April 22, 2016, 09:49:39 AM »
Interesting thing I saw the other day...

El cheapo, Chinese taser cum cattle prod.... to charge, it simply decoupled the mains input with a capacitor on one line and straight thru a bridge rectifier to a battery pack.... I don't think it is possible to get a more horrible a charger than that.... Strange enough, the rest of the unit has fallen apart from a mechanical standpoint but the electronic/electrical side is still 100%...

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BruceM

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Re: Charging a 6 volt off grid?
« Reply #13 on: April 22, 2016, 04:23:47 PM »
Using a capacitor from the mains to reactively limit current and voltage is commonly used in cheap LED lamps as well.  You get about 0.050 amps (50 ma) per 1 uF at 120VAC 60Hz. Rectify it and away you go.

For small amounts of power it can be cheaper and more compact than a transformer.  Power factor is of course horrible.