Lead Acid battery charging question

Hi Pal (no pun intended),

The 24v lorry and tractor batteries are quite cheap in Suffolk-UK as compared to 12v car batteries. A comparison of say £25 for a GIGANTIC 24v battery as compared to £40 upwards for a super-duper car battery with a

1000-year guarantee (or whatever they're pushing now). The 24v batteries are also not maintenance-free which means you can have some control over keeping them in good health, higher Ah capacity too.

Oh charging.. At low amperages a battery will take to some extent what it needs (1Ah) and then generate heat, but at the higher Ah it can definitely burn off the electrolyte, actually if left continually charging the chemical process will kill the battery (my brother used to have RC cars which are charged from a 12v and leaving them on charge continually to try to recondition them killed them). Also, car type batteries shouldn't be deep-cycled as in almost drained and then repeatedly charged over an over, a car battery will perhaps survive a dozen of these deep discharge/charge cycles before the plates sulphate or buckle. Although I haven't looked I'd bet that those 24v tractor batteries have thicker plates.

Actually this is something I've been looking into lately so have an interest in this ..windpower and batteries etc. Most applications suggest the sealed deep-cycle (very expensive) LA batteries.

200w ..PVC ..that's 200w / 24 = 8.3Ah. That turbine on a good day will be kicking out 8.3Ah. So ...400Ah battery will take 400/8 = 50 hours to charge in perfect conditions. May as well halve all of those figures for safety sake, 100w, 4Ah, 100 minimum hours to replenish 400Ah.

At a guess I'd say that you need some electronics gizmo to step down to 12v and to isolate the two batteries. Still I'd go for a 24v battery since an element of efficiency will be lost in the conversion before the charging even begins.

Perhaps try approaching a rural garage which services tractors in the back end of no-where.

;^)

It might even be a bit better than that. 200w is a nominal rating, but the supplier claims to have measured 300w in high winds.

I have been toying with going all 24v. I can get 24v compact fluro lights from the same wholesaler for about the same price as the 12v LED lamp assemblies I had intended. They use about 4 times the power but give 5 or 6 times the light. With LED lamps though, as there would be more of them, I could only switch on 1 or 2 for lower light and power consumption levels. At about 0.8w each, they should run for days without wind!

The main problem is everything else. Just about everything I already have is 12v. Every device I am aware of off the top of my head that does a 24 - 12v reduction is based on some sore of a voltage divider circuit, and would therefour introduce huge inefficiencies which I intend to avoid.

Perhaps I should research that issue a little more before I wire everything up.

My shack is at the back end of no-where! Maybe I should try the roadhouse!

Regards,

Pal

back

Ello ;-)

Mmmm, 24v to 12v, yep I understand. Don't have a need for hot water do you ;-) A resistive load in the circuit could take that down to 12v if what you're powering is consistant. The resistive load generating the heat.

So complicated isn't it!? Trying to decide what's best, well trying to decide really when in effiency drive:-)

I'm by no means an expert here, just someone who has thought about the things you're going through.

24v to 12v conversion. Just wondering about the energy that'll be lost. If the turbine was chucking out 12v at 200w then that'd be some 16Ah. But converting from 24 to 12v something will be lost. Could convert to AC and then AC back to DC, again some loss. Actually... you can let transformers self resonate (or whatever it's called) and they'll do it at their most efficient frequency, flyback configuration but it'll be very low amps. Dunno. We have an old 12v-240v invertor in a shed somewhere here which is like an electric motor (it spins), another avenue maybe for the amount of amps involved.

I'm sure as we're having this discussion and wildly throwing things up in the air that the other readers will come back with solid info. So I guess the immiediate questions is 24-12v efficiant conversion that can handle the ampres.

tml

The trouble is that you're/we're in a position where you can spend so much on the associated kit that it defeats the object of saving money/resources in the first place. The ideal kit would be something which you can build cheaply yourself and can maintain indefinitely.

The turbine itself is actually a 3 phase AC device. It's the charging regulator that comes with the kit that drops it back to 24vdc for the batteries.

I've just about decided that 24v battery(s) are the way to go, as that will still work for the lights, and I've found a local electronics retailer that stocks an electronic 24 -> 12vdc converter that can supply

20a @ 12v constant, which should be more than enough for everything I envisage using at any one time.

The idea of a water heater is a little humerous... it would be predicated upon having a supply of water, which is somewhat of a luxury item where the shack is located, deep in the back blocks of South Australia (the driest state, in the driest continent on the face of the earth!) We have a 500 gallon rainwater tank, but I've never seen it full... Washing is done by the bucket, not by the bathtub, and the only heating required, is to leave the bucket standing in the sun for half an hour or so.

Regards,

Pal

A 12v swiching regulator is the right solution for your problem, quite easy to make these days.

Ahhh I understand how remote you mean now. I was about to suggest a fuel cell, as in separating water into hydrogen and oxygen through electroysis. But if water is in short supply that could kill that one. Actually... With the water separated into hydrogen and oxygen... Wouldn't evaporate would it ;-) Would need an element of pressurisation though.

Mmmm, you could have a system set up which captures what water does rain, seperates it into H and O. Then when you go back weeks later you have electricity on demand with water as the by-product.

Oh the ideas... ;-)

You should be able to use 12 Volt batteries in series. You can use the tap between them. This sort of thing is done often, and it is an easy and low cost solution.

If you get in to voltage inverters or voltage regulators to go from 24 Volts to 12 Volts, then you will get in to the situation if you want a very high current, the cost of the inverter will be very high. Using resistors is out of the question, because there will be no regulation.

If you want more amp hours, you can also put batteries in parallel ( For example, 2 sets of series batteries wired in parallel.), but make sure that all the batteries are the same, and that the generator sees 24 Volts for its charge load. You can put parallel sets of batteries on to the generator, as long as the charge current will not exceed the rating of the generator, if you want more Ampere hours.

I have found that with wind generators, when the weather is calm, there is a lack of charging current. If you are going to locate the wind generator facing out to the ocean, then you will have better conditions for wind.

--

JANA
_____


"Pal"  wrote in message
news:43d1dbd7$1@dnews.tpgi.com.au...
Hi Folks,

Have just picked up a low power ( about 200w ) wind powered battery
charger, that I plan to install on the family's holiday shack that has
no mains power.

The charge regulator that comes with the kit regulates for charging a
24vdc battery.

Most of the load devices I plan to use are of the 12v variety
(automotive) as they are cheap and plentiful.

My plan is to bolt two 12v batteries in series to connect to the
charger, and use a tapping between the two batteries to give me, in
effect, two separate 12v supplies. One for all the 12v lights, and the
other for everything else (radio, small water pump in the shower, and
maybe a fan).

My question is this...  As the two batteries will obviously discharge at
different rates given their different loads, will a single charger cause
problems with over charging one battery while under charging the other?
Or would this effect be so small as to be insignificant?

Thanks in anticipation,

Pal

It CAN cause problems,as you are already aware,but it's been done before..

The problem is with unequal charging/discharging,one batt gets "cooked" while the other may not ever be fully charged,depending on the load imbalance.

Try to keep the load on both 12V "legs" as equal as possible,amp for amp. It might also be good to swap the batteries around once a month or whatever,to help keep them balanced,and in similar condition.

is a good site for more info/questions.

Try a 24-12V down converter..

Precisely what I eventually decided to do. Have already got a unit rated at 25A peak load, 20A continuous, which should be fine for the limited number of devices I plan to use.

Thanks for your suggestions.