Advice needed regarding circuit with SLA batt in tin shed

Jason S · 2005-12-03T20:57:39+00:00

Need some advice!I am designing a circuit for a small tin shed that requires backup power from a 12V SLA battery. It's an alarm with added features such as LED lighting and other additional features.All the circuitry will be in a "IP65 Sealed ABS Enclosure" (Size HB-6132) from Jaycar Electronics, which has pretty thick walls, and inside the box will be a small 12V SLA battery that will be kept on float charge (for backup) and the PCB's to make it all work, including the power supply/charging circuit.My concern is the heat in the shed which may affect the SLA's performance. I read that the batteries should not be stored/charged in high temperatures. I'm sure that it won't reach the same temp inside the box if it's sealed and unvented, but I will probably need to vent the box because of the components that generate some heat - or is it not essential?. Inside the box will be some aluminium sheeting surrounding the walls as heatsinks. On a hot summers day, the temperature inside the shed can reach 45-50 degrees celcius quite easily, as there is a lack of ventilation.- What do you reckon?Should I keep the box unvented to keep the battery cooler than the shed's ambient temp?Should I vent it and maybe use a fan (when it starts getting exceptionally warm)?Other suggestions?Note that the float charger will have temperature compensation to keep the voltage correct.Any help will be much appreciated.Thanks,J

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GotCoffee 20 years ago

If the bat only cost $20, leave it outside the box, next to the box- ventilation problem solved. If the bat is a SLA 12V 7A bat, it will survive the heat with no problem. I have a couple SLAs that I use for radio control and power loss lighting/radio that stays in my garage. I live in the desert where the outside temp gets up to about 120 deg F or 48.9 deg C. The garage reaches temp of 130+ F. These bats are three years old and still work great.

Bottom line, put the circuit in the box, the bat next to or on top of the box and the whole thing in the shed. If you run into a problem, bury the bat. and worry about water, rain, solvent spillage, and rodents chewing up the underground stuff.

I would use an old paint can to put an alarm system into so if someone broke into the shed first, they wouldn't "recognize" the box right away.

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J

Jason S 20 years ago

Hi, Perhaps you have a different type of SLA? My battery will be of a minimum of 1.3Ah - probably will go higher if I use the underground method because I'll have more space in my circuit box. Yeah I agree about the water, spillages and underground rodents, and is bit of a worry now that you mention it, but I think it should be ok as long as I use the proper materials suitable for underground.

Ta, J

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J

Jason S 20 years ago

haha, no no, I don't give up THAT easily =) It's a challenge for me. I'm sure I'll find a solution.

J

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Jason S 20 years ago

OOOHHHHHHHHH, NOW i know what you meant by that! I thought you meant ditch (bury) the whole idea if doing this project!!!!!! haha. Sorry. Yeh I think it's a great idea actually, because it can be done quite easily.

I actually thought it may work because then it will give me more room in my circuit box, and the battery will be kept cool no matter the ambient temperature. I will probably run conduit down and drill some holes through the conduit just above ground level so any gases from the battery can escape (it won't be a very deep hole don't you worry). Thing is, not sure what type of enclosure to use for the battery, and how big it should be, etc. Length of the wire is also a concern as I don't want to experience any power loss (type of wiring I should use?). Distance shouldn't be more than 2 metres I would say.

J

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Jason S 20 years ago

Ok. Thank you all for replying. It's getting hard to keep up with all of you individually now.

Yes a sealed enclosure is bad bad bad without ventilation. I now realise that from all the replies, thanks. Some of the suggestions made as a potential solution were clever, but cost, space and power consumption (for cooling etc) were things I had to consider.

A couple of you came up with the idea of keeping the battery under-ground. I actually thought it may work because then it will give me more room in my circuit box, and the battery will be kept cool no matter the ambient temperature. Digging a hole wouldn't be difficult to do. I will probably run conduit down and drill some holes through the conduit just above ground level so any gases from the battery can escape (it won't be a very deep hole don't you worry). Thing is, not sure what type of enclosure to use for the battery, and how big it should be, etc. Length of the wire is also a concern as I don't want to experience any power loss (type of wiring I should use?). Distance shouldn't be more than 2 metres I would say. Unless I recieve lots of negative feedback about this, I will probably end up going ahead, but I would like to say thank you all for your suggestions/feedback if I haven't gotten around to doing that already.

Thanks again, Jason

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C

Chris Jones 20 years ago

Yeah sorry I should have pointed out that you said it already. Since it seemed like a good idea to me and noone seemed to have read it, I thought it could do with saying again. I think maybe a concrete drainpipe set vertically into the ground with a plastic container inside might do, as an alternaive to the plastic drainpipe, whatever is cheaper/easier to do locally. As others have said, there needs to be a vent for the gases.

I have some lead acid batteries that have lasted well over a decade and are still going well, and I suspect it is because I keep them cool.

Chris

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Jason S 20 years ago

Well i was thinking a plastic box inside a wide PVC drainpipe with cap and the conduit running out from both (not forgetting the vents for batt gases). Don't think I really want to use concrete piping.

J

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