charging 7AH sealed lead acid battery

The solar panel would do at a pinch just check that it has a regulated voltage output of around 13.8V if you intend to leave on float charge.

Same for the thumper, it should be ok and I would expect it to also have a regulated output of around 13.8V

Cheers,

Leigh

G`day Kc,

If you can find one of the small black chargers that are used with some electronic stuff that have the three pins to fit a normal 240v power outlet as part of it they are just the ideal thing, there are often boxes of that stuff at Sunday markets,garage sales ,etc.
Read the label to make sure it says "Battery Charger" and not "........ Adapter", it also should say what the voltage and output amps are.
For a 7ah battery 600ma or 800ma is good.
You may be able to buy one at the likes of Jaycar, Dick Smiffs, etc. not very exy I wouldn`t think.

I use one of these to charge the same battery as yours for my sounder.

Scrubby.

Give the little solar panel a miss - 50mA is not enough (won't be enough hours in the day!)
It is quite likely that your 12V 1A charger is suitable. Measure the voltage while charging the battery and if its around 13.8V, then you're OK.
Also for $20 you can buy a SLA battery charger from Jaycar.http://www.jaycar.com.au/productView.asp?ID=MB3517

You can also simply charge it in your car. Jaycar sell a fused male/male cig socket for this purpose. On previous vehicles, I charged the 7Ah batteries via a relay that is powered whenever IGN is on.

There are a couple of issues with charging 7 AH sealed lead acids.

They are a small battery and in general have a limited maximum initial charge rate.

Y want to charge em fast enough to be convieninet, but not so fast they get hot and blow up.....serioulsy...... I've seen em with the top split of em and blown up like a balloon, when the vent valves have not worked, in installations that where not properly current limited.

Best maximum charge rate is between 1 and 1.5 amps.

If you have 240V available, one of the cheap common sealed lead acid chargers from jaycar, altronics or similar will work well.

I run several of these.

At this rate they will charge a near flat battery in about 10 to 12 hours....a half flat battery in about 6 to 8.


they mostly have a light indicator that shows charge ready.

Charging a small sealed lead acid from a vehicle is a little more complicated.

I have done some research and some actual experiments.
If you connect such a battery direct to the charging system of your car you will very likely over heat it.

I hooked up a fairly healthy near new 7 AH sla direct the the battery of a vehicle with made up cables and with the alternator running at 13.8 vots, it got rather hot rather quckly and arround 12 amps flowed.....disconnected rather smartly.

SO if you want to charge in your car, you have to introduce some sort of current limiting.

People have used light bulbs, and they are moderately effective...others have used resistors.

I have tested both......A light bulbs is quick easy and no maths required...use a 12 volt 21 watt light bulb in series with the positive lead and all will be well.....but the battery wont charge real fast....you can move up to bigger light bulbs or more light bulbs....but ..yeh there are better ways.

A good quality high power resistor is far more predictable and far more consistent than a light bulb...but there is a trade off of current limiting V charge speed.....sorry cant remember resistor values but ther where under 10 ohms

Its not easy to calculate, you have to establish the value by experimentation.

People have raised the method of using three terminal voltage regulators....they are great if you have enough voltage to spare... they will regulate to the correct voltage AND do the current limiting for you.....BUT you do need a good 18 volts or more before the regulator to achieve a reliable 13.8 volt output to the battery.
At some point ...about 2 to 3 volts above the charge voltage the regulator will,shut down.

So the 3 termainal voltage regs are no use in the car..

Wat has been proposed is some sort of switchmode inverter to achive sufficient voltage off the 12 volt supply and the regulate down to the 13.8 volts with a 3 terminal regulator...yep that will work....the quickest way to achieve this is to buy a dc to dc converter lap top computer supply and regulate down to 13.8 volts with a 3 termianl reg.

All this can be had from Jaycar or altronics.



BUT
there is an easier way.

There re pre built ready to go boards that will do this available from ebay.....what you want is a DC to DC converter board that is current limited at arround 1.5 amps or has an adjustable current limit.


I have not got arround to trying any of these ...but on paper that would be the best solution with the fastest practical charge rate.

Hope this all hepls

cheers

Jay car have plenty of charges for them at about $20 to $30 dollars

Thanks everyone for your input... much appreciated. there is a lot of detail here and i will need to re read a few times as I am interested in understanding how this works. I have dug through my bin of chargers and adapters and found a ryobi 12v 400mA charger. I hooked it up to the battery and it looks like it will fit the purpose well. It is on charge at the moment and it will be interesting to see what voltage it takes the battery up to. I dont need a quick charge so 400mA will be fine. While going through the bin i was surprised to find battery chargers, adapters and power supply printed on the various items although to my untrained eye they all seemed much the same. The power supply for the battery booster i already have does not say what it is, just output 12v 500mA. The 240v charger that came with my uniden uhf handheld radio says it is an adapter so this adds to the confusion. I expected it to say charger. I also googled the voltage regulaters and found that quite interesting. It leads me to this question. What is the difference between a power supply, adapter and battery charger? Would they all be regulated to 13.8v if they are intended for 12v use?

Thanks again

Kc

KC

Just to throw something else in here that is a little out of the square, it sounds like a standard 12V 7AH battery they use in most small UPS's.

Some of these UPS's are small enough to not be a pain in the butt to use as a simple battery charger - while they are not "smart" they are designed generally to re-charge and float these types of batteries.

If you had access to one of these it may be a good simple ready made option.

I have heaps of them if you are in WA, but if not you may find any larger IT company (not retail stores) that service businesses would have old ones they may have recovered from businesses.

They usually "don't work" simply because the battery in them is stuffed and not because the UPS itself is faulty. As long as you hook up a reasonably healthy battery the UPS will normally start and recharge the battery. A little adaptation to bring the internal battery leads external to the case and you have a pretty simple 12V SLA charger for 7AH batteries. Note however they probably will not have short circuit protection on the 12V leads as a normal charger does.

Surely any basic automotive batter charger you can buy from Repco or Supercheap will work fine. I have one that charges at 1.6 amps and another that is a max of 3 amps. They charge bike batteries Ok and car batteries that are not dead.

Something like this - click here