Car or lesuire battery for home power storage?

uktyler

I'm looking at setting up a small 12 volt home power grid, to power phone chargers, battery chargers and outside lights. I will be using a small wind turbine and solar panels to supply the power, but what batteries are best?

Will I need an overcharge circuit if all the batteries are fully charged?

Lesuire batteries are expensive, whilst second hand car batteries are cheap, can I get away with using car batteries?

Thanks

rare_stuff

Whilst not being an electrician I do have a little experience of living 'off-the-grid', whilst living on a narrowboat with solar panels and a wind generator which provided all the electric, about 99% of the time.

You will need an 'overcharge circuit' to stop batteries overcharging, not sure if that's what it is called, the solar panels didn;t require one, just a beefy diode so current didn't leak up it. The wind genny had another thingy, probably the overcharge circuit, it was mounted on a medium sized heatsink, about the size of cigarette pack, and when the wind roared this did get warm!

Overall the wind genny did provide more electric in the winter, but the noise and vibration was quite something in strong winds so it was often turned out of the wind when it was very windy. On those still days the solar panels did keep trickling in power, even in the heart of winter. The only times we had to rely on a backup was after about a week of no wind in the middle of winter.
The solar panel was great all year, even charging on dull rainy days, though you would get twice as much power on sunny ones.

As for batteries, well, if you use old car batteries they will be knackered pretty soon as they are very different to leisure or 'deep-cycle' batteries. Car batteries are designed to discharge very quickly to turn the starter motor and recharge very quickly off a high amp circuit. Leisure batteries are deisgned to charge and discharge slowly. Although in the short term both could do the job of the other, it would dramatically cut their working life if done so, considerably if you used a leisure battery for starting cars!

Wind turbines are pretty expensive bits of kit, and solar panels aren't that cheap either. You may be better off buying these things as they already do exist seperately. Shed lights powered by solar, wind-up and solar phone and battery chargers, there is even a micro turbine for charging your phone available! So, you could try reinventing the wheel, or you could just checkout a few eco-stores for these items, If you need a hand finding some, drop me a pm.

uktyler

I won't be buying a wind turbine, I will try to make my own. I had a friend years ago who built one using a bike wheel and car altenator. I don't think it was too effiecent, but it worked.

I will probably use the dynohub designs, cheap and simple to build, like this one:
http://uk.youtube.com/watch?v=N3jSmYcv6zE&feature=related

A_fiend_for_life

Not actually done it myself but...

A car alternator relies on a regulator that cuts out at 14.2 V (or VA whatever the units are) so not sure that you need an overcharge circuit* for that if you're keeping the regulator. The alternator works by negative feedback if the charge is low the excite circuit current is high and so more electricity is generated. If charge is high the excite current is low so less charge is generated.

*I'm not quite sure how it works nor how other turbines work so I might be wrong. I am wondering if this is a separate battery bank that charges once the primary bank is fully charged!? If so it would be a good idea.

Lucas ACR15, 16, 17 or 18* are the cheapest for parts and to buy not sure if they are the most reliable though. The higher the number the higher the current they can generate. The advantage of the lucas ones is that you only need to remove the cap to get access to the regulator, diodes and brushes. Delco-Remy and Bosche you have to split in half to get access to the regulator, brushes, rectifier and excite diodes (the excite and rectifier diodes are separate in both these models). They were more expensive but probably because they were imported.

You will need to water proof it.

There is also a 24 volt lucas alternator. ACR23* I think.

*They are the catalogue numbers as best as I can recall.

rare_stuff

A_fiend_for_life wrote: »

*I'm not quite sure how it works nor how other turbines work so I might be wrong. I am wondering if this is a separate battery bank that charges once the primary bank is fully charged!? If so it would be a good idea.

Basically the overcharge circuit worked on the principal of a resistor, heatsink and some circuitary to sense when the batteries were fully charged.

There's little point in having a secondary bank, if you have the batteries just connect them up. If I recall from a visit to CAT(Center of Alternative Technology) they had a shed filled with batteries, and many of these were ex-tank batteries. Though I think they were generating and storing quite a bit of power for the centre from this shed!

A_fiend_for_life

So the excess is dissipated as heat?


Edit: No! I presume this is just a negative feedback circuit by another name.
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uktyler

rare_stuff wrote: »

There's little point in having a secondary bank, if you have the batteries just connect them up.

This is why I was thinking of using car batteries, I could get 10 or so batteries from diesel cars for the price of one leisure battery.

Given enough batteries and a step up transformer I could power mains voltage items too (providing the wind generator and solar panels can restock later)

mech_2

I wouldn't use a car alternator. The efficiency is lousy and they need higher RPM than a wind turbine can offer without gearing. You basically want something which can be directly fixed to the blades and has permanent magnets in it. The dynohub thing looks ideal.

rare_stuff

If you can get a bunch of car batteries very cheaply then it's worth trying, but there are huge differences in the design of car batteries and leisure batteries as I said earlier, so don;t expect the car batteries to last very long.

If you are looking at powering mains voltage items you will need to get a decent inverter to do so. Depending on the wattage of what you will want to plug into it, will denote how big an inverter you will need. You can get inverters quite cheaply but the cheap ones do tend to be very low wattage and will power no more than a phone charger or 2, or maybe even a laptop charger. To power much more than this and inverters start to get expensive.

You mention building your own turbine, and using an alternator, I'd do some research here as I believe looking for a dynamo or magneto may be far more worthwhile. Alternators do need to be turning quite fast and have quite a large amount of resistance to turning and may not be suitable for something the size of wind genny, I'm not sure but I think there was also another reason why they aren't suitable for diy wind generators.

It sounds like a great project and I wish you luck with it!
these links may be of use to you -
http://www.treehugger.com/files/2008/08/cheap-diy-wind-turbine.php
http://www.otherpower.com/otherpower_wind.html
http://www.scoraigwind.com/

uktyler

Thanks for all the info, i want to try a small setup to see if the site can handle a bigger one. If the 12v system works I will be investing in a larger system, with grid tie in.

The 12v system will just be a cheap trial, I can use car lighter sockets to power chargers for phones and the laptop in the house, and for lights in the garden. I am trying to get some leisure batteries, however they are a lot more than car batteries, can I mix and match?

rare_stuff

sorry for the delay in responding -

You can mix & match leisure batteries or car batteries of different ampages, but it would not be advisable to mix car and leisure batteries on the same circuit due to their different charge.discharge characteristics.