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Battery and Solar Stuff

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Dancin David

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I tired to read some older posts so as not to make a new thread that had already been covered, but couldn't find one that I could actually understand....

first off, I can get a few 12v 7ah batts for free from a friend, so Im trying to go with that for now (no spending required).

So I have some specific questions:

1) If I have a 12v 7ha SLA battery, in theory, shouldn't I be able to run a 1 amp circuit (using anything less then 12v's) for up to 7 hours, at which point the voltage would be 0v and need to be recharged - If this is the case, how can I get 7 Amp Hours out of it if its not allowed to drop below 10.8 volts ? (I might have asked something really dumb just then, but I'm prepared to be mocked if need be)

2) can I put two 12v 7ha SLA batteries together to get 12v 14ha? or will I just get 24v 7ah?

3) Lots of solar panels out there, lots of batteries and lots of solar regulators... so what kind of panel to suits what kind of regulator to trickle charge a 12v 7ah SLA battery? (or what do I need to charge 2 or 3 of the same batteries, as above)? - would like to learn the concept, not just be pointed to a particular product, if you know what I mean....?

Thanks to all in advance :)

Dancin
 
I tired to read some older posts so as not to make a new thread that had already been covered, but couldn't find one that I could actually understand....

first off, I can get a few 12v 7ah batts for free from a friend, so Im trying to go with that for now (no spending required).

So I have some specific questions:

1) If I have a 12v 7ha SLA battery, in theory, shouldn't I be able to run a 1 amp circuit (using anything less then 12v's) for up to 7 hours, at which point the voltage would be 0v and need to be recharged - If this is the case, how can I get 7 Amp Hours out of it if its not allowed to drop below 10.8 volts ? (I might have asked something really dumb just then, but I'm prepared to be mocked if need be)
The SLA capacity is rated over the 13.8Vnom to the 10.8Vnom points.

2) can I put two 12v 7ha SLA batteries together to get 12v 14ha? or will I just get 24v 7ah?
If you connect in series you get 24V at 7Ahr, shouldnt really connect them directly in parallel

3) Lots of solar panels out there, lots of batteries and lots of solar regulators... so what kind of panel to suits what kind of regulator to trickle charge a 12v 7ah SLA battery? (or what do I need to charge 2 or 3 of the same batteries, as above)? - would like to learn the concept, not just be pointed to a particular product, if you know what I mean....?

Thanks to all in advance :)

Dancin


Hi,
IIRC its Melbourne Australia.?
If you want to recharge a 12V 7AHr battery, you need 14V at 1Amp for 7 hrs * 1.5 OR 7Amps for 1hr *1.5.

Thats if the battery is in good condition and you start from 10.8V.

NEVER discharge the battery less than 10.8V or you will ruin it..

Look here:
**broken link removed**
 
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Another dumb question - x 1.5 what?

hi,
These are only approx charging figures.

If you charged a 7AHr battery at 1amp for 7 hours it would not be fully charged, because the 'charging energy conversion' is only about 60% efficient. Say 50%

So 7 hours * 1.5 = 10.5 Hours. Say 10 hours OK.?

Some sources claim 90% eff, its my experience its more like 60% to 70%
 
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Aha... Im starting to understand... can you confirm these for me...?

If I know the approx amp usage of something, can I tell how long to drain from full charge to 10.whatever ?

Also, using a 14v 1A solar panel would mean that I need approx 10 hours of sunlight to recharge it, right? (approx)

Sooo... if I had a 14v 7amp solar panel, I could theoretically charge it with one hour of sunlight? (approx)

I guess all this depends on how fast my system drains the battery... If my system only uses a tiny bit of power all night, its possible that 4 or 5 hours of sunlight the next day (using a 1A panel) might be all it needs to recharge the small bit that was used, right?

Thanks again Gibbzy.. you rock
 
If you connect in series you get 24V at 7Ahr, shouldnt really connect them directly in parallel

Sooo... would it still share the voltage loss over the two batteries? Like if a circuit took 1 battery to 10.8 volts in say... 1 hour, would having 2 batteries in series mean that the same circuit would take each battery to maybe... 12 something Volts over 1 hour?

Just curious...

Thanks
 
Sooo... would it still share the voltage loss over the two batteries? Like if a circuit took 1 battery to 10.8 volts in say... 1 hour, would having 2 batteries in series mean that the same circuit would take each battery to maybe... 12 something Volts over 1 hour?

Just curious...

Thanks

If you started at 24V [charged] you would stop when the 24V dropped to 21.6V.

Is that what you mean.?

What load/circuit you are driving with this batteries.?
 
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The battery document says to limit the charging current to 0.2C. For your 7Ah battery then the current should be limited to 1.4A. The current will be 1.4A for about 5 hours then it will drop gradually for the next 5 hours.

Your solar panel makes its rated current only at noon in the Sahara desert so it might not charge the battery in one day where you live.

The amp-hours are rated at a 20 hour rate. So your 7Ah battery provides 350mA for 20 hours. I can't see the graph well enough to see how little is the duration at 1A. Maybe only 2 hours.
 
It is a bit tricky to do but since solar panels' maximum power output vary so much with environment an intelligent charger is best.

The maximum power is available at a particular output voltage that varies with the environment. You regulate the panel voltage by varying the load current and then slowly adjust the desired panel voltage to track the peak current. I do not think it always responds in the same direction since there are so many variables so a simple opamp circuit would not work.
 
Well a 12 volt 7 amp solar panel would cost close to $700 just to charge 7ah batteries :eek:. If your serious about using PV for battery charging try getting some decent deep cycle batteries. The 12 volt 7ah batteries are only used for light duty backup or expect 3-4 months life out of them. One golden rule to remember with sla's or vrla's is they like soft discharging for long term use.

Cheers Bryan ;)
 
Thanks to everyone for your responses, I am learning a great deal.

By the sounds of it an SLA is not the way to go for something that is going to be used on a day to day basis (even if low V and low Amp).

at the end of the day its only 18 LEDS at 20mA each - They require about 3.4 volts each - but Im thinking of just getting some D sized 9000mAh and using those (I would have to put a few in series to get over 3.4 volts but that seems a lot cheaper then a deep cyc. just to run 18 LEDS)

With that said, should I get NI-MH or NI-CD? and can I get good solar charges for these?

Thanks again to everyone
 
Thanks to everyone for your responses, I am learning a great deal.

By the sounds of it an SLA is not the way to go for something that is going to be used on a day to day basis (even if low V and low Amp).

at the end of the day its only 18 LEDS at 20mA each - They require about 3.4 volts each - but Im thinking of just getting some D sized 9000mAh and using those (I would have to put a few in series to get over 3.4 volts but that seems a lot cheaper then a deep cyc. just to run 18 LEDS)

With that said, should I get NI-MH or NI-CD? and can I get good solar charges for these?

Thanks again to everyone

hi David,
I wouldn't buy Ni-Cd batteries, I prefer Ni-MH, BUT you could buy a 12V lead acid car battery, say 40 or 60AHr.
Even a second car battery would be suitable for driving LED's

Connect 3 * 3.4Vleds in series, [10.2V chain] , run at 20mA/chain.
Thats 6 chains at 0.02= 0.12A.
A 60AHr battery would last about 500hours.!, charge it from the mains from time to time.
 
One golden rule to remember with sla's or vrla's is they like soft discharging for long term use.

To put it another way, the rule of thumb is to not discharge a sla battery more than about 50% to maximize the lifecycles (dishcarge/recharge). Look up an sla datasheet, and they usually will show a chart on this.

Nothing the matter with the FREE 7ah sla battery's in my opinion. Should fit your energy budget. Get a cheapy low amp analog charger like the Morningstar Sungard or? Put the solar to it and you are good to go. The solar panel is a bit tricky and the most expensive item. So a panel that gives out one amp should be close, 10-20 watt range?

My two cents.

Edit: Ok no product indorsements, loads of battery charger chips out there, maybe someone will recommend one.
 
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best laid plans...

Ok, been reading lots and learning lots...

Here's what Im going with after all my posts and dumb questions - can someone take a look and tell me if this is the realm of correctness (or even the realm of possibility):

- 18 leds (20mA each, 3.2 volts each, split in to banks of 3 leds with the correct resistor to ensure each only gets its 20mA)
- turning on at night with my twilight switch kit
- Running all night and trickle recharging during the day
- Building my own simple solar charger to charge a bank of 10 AA nimh batteries in series (2000mAh or 2500mAh)

As for the the solar panel:
- Jaycar has a large-ish 12 volt panel that produces 250mA (perfect for the 2500mAh AA's)
- Or Dicksmith have a much smaller 2 volt panel that produces 200mA (I would need 6 panels in series, but would suit the 2000mah AA's perfectly)

*Both solar panel options cost about the same and would mean that I would not need to worry about 'current limiters' because at full sunlight, each option would produce the recommended 10% current for the batteries. And according to my reading if you keep them at 10% percent, overcharging is not so much of an issue (nothing a new pack of batts wont fix if its wrong)

Does all that sound about right to everybody - no major misconceptions that will get me blown up or burn my pergola down?

Looking forward to feedback
 

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Ok, been reading lots and learning lots...

Here's what Im going with after all my posts and dumb questions - can someone take a look and tell me if this is the realm of correctness (or even the realm of possibility):

- 18 leds (20mA each, 3.2 volts each, split in to banks of 3 leds with the correct resistor to ensure each only gets its 20mA)
Thats OK.

- turning on at night with my twilight switch kit
Thats OK
- Running all night and trickle recharging during the day
Depends on the Sunlight.. but no hazard.

- Building my own simple solar charger to charge a bank of 10 AA nimh batteries in series (2000mAh or 2500mAh)
A little complicated, but possible.

As for the the solar panel:
- Jaycar has a large-ish 12 volt panel that produces 250mA (perfect for the 2500mAh AA's)
I go for this version 20% more ummph.

- Or Dicksmith have a much smaller 2 volt panel that produces 200mA (I would need 6 panels in series, but would suit the 2000mah AA's perfectly)

*Both solar panel options cost about the same and would mean that I would not need to worry about 'current limiters' because at full sunlight, each option would produce the recommended 10% current for the batteries. And according to my reading if you keep them at 10% percent, overcharging is not so much of an issue (nothing a new pack of batts wont fix if its wrong)
Sounds OK to me.

Does all that sound about right to everybody - no major misconceptions that will get me blown up or burn my pergola down?
Sounds OK, always have a suitable fuse in the battery circuit.

Looks OK.

Whats the resistance of the relay and the type of transistor that drives it.

Strange question, but as an earlier respondant pointed out it could be possible to drive LED's with the transistor instead of the relay, would save power, better endurance.
 
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Looks OK.

Whats the resistance of the relay and the type of transistor that drives it.

Strange question, but as an earlier respondant pointed out it could be possible to drive LED's with the transistor instead of the relay, would save power, better endurance.

Umm.... he's all that I know about it:

BV1719
6V
106 DM
Its blue :)

I did try a really simple LDR circuit earlier in the game, got it to work with light but when I switched it round to be a dark sensor, it would not work. Happy to try again, but would love for someone to tell me what I need with regards to my specific requirements and give me the exact, trimpot, resistor, transisitor values I need....
 
The relay in the Twi-light kit wastes a lot of current. The relay can be replaced by a transistor that will not waste current.

I don't know the total amount of sun per day at your location. The solar panel produces its rated output only at noon in the Sahara desert so its output will be much less at your location. Before noon and after noon the sun is less intense and at the wrong angle for the solar panel which reduces the output.

If you use a 250mA solar panel and its average output is only 50mA for 10 hours then your 2500mAh cells will be only partially charged.
I think you need a much more powerful solar panel and a current regulating circuit.

Of course the LEDs will not light for long during a night following a cloudy day.
 
Umm.... he's all that I know about it:

BV1719
6V
106 DM

hi,
I cant get a fix on that relay number.???

Question, why do you want the light to stay ON allnight, rather than say, from dusk until bedtime..?:)
 
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I don't know the total amount of sun per day at your location. The solar panel produces its rated output only at noon in the Sahara desert so its output will be much less at your location. Before noon and after noon the sun is less intense and at the wrong angle for the solar panel which reduces the output.

If he does live in Melbourne as someone suggested in an previous post, then he would be at the same same latitude as the Sahara merely on the southern side. Any further north in Australia will simply allow more power to be produced.
 
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I looked on google Earth and found that the Sahara Desert is pretty far from the equator. Melbourne is much farther, about the same latatude as the south of Spain and the south of Greece except in the other hemisphere.
 
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