WHAT 12V BATTERY DO I NEED ?
Paul Batty (E-mail: firstname.lastname@example.org )
Many moth-ers ask about suitable batteries for running their equipment, so I've written a few guide-lines below to help select the right battery. FIRSTLY: If you want a happy life, DON'T use 12V moth portable gear, always use mains. However, if you like a challenge - then read on...............
WHAT TYPE? For running 12V moth gear, the best batteries are CYCLIC or DEEP DISCHARGE type batteries. Leisure batteries usually fall into this category. LITHIUM batteries are ideal if you can afford them. Rechargeable NiCads & NiMh in packs can be used for running smaller tubes or UV LEDs for short periods UNDER SUPERVISION.
CAR BATTERIES are not ideal, but often offer the best value for money, or you may just happen to have one knocking around..... However, if subjected to continuous deep discharge, some car batteries can suffer from collapse of the plates or sulphation. STANDBY BATTERIES out of alarm systems etc, are generally unsuitable (although I've spoken to folks who use the old batteries out of alarm systems when these are upgraded, and they tell me they work fine. It's amazing how praiseworthy things are though, when they are free !
HOW BIG A BATTERY DO I NEED? Well, the bigger, the better really. It all comes down to how far you intend to carry it. You can use the following formula to work out how big a battery you need.....
Trap current (Amps) x Running time (Hours) + 20% = minimum Ah rating.
And if you have a solar switch fitted and want to leave it turning the trap on and off for several nights then bear this in mind when you enter the "running time" figure. A solar switch won't work if your battery has gone flat ! - Involve a solar switch and you really need to jump up to the next battery size, or double your battery. PLUS, you're bound to get over - confident and think your battery will run the trap forever. IT WON'T !
A rough guide to working out the current drain of your equipment is to divide the wattage by 12 to give you a figure in Amps. Watts = Amps x Voltage. 8W tube uses approx 0.7A, a 15W tube uses approx 1.3A, a 22W or 25W tube uses around 2A and a 40W uses 3.3A.
So if you want to run a 8W Actinic trap for 5 hours every Friday night in the Garden Moths scheme, the smallest battery you can use is: (0.7A x 5h) + 20% = 4.2Ah. [But always go bigger if you can - MUCH bigger !]
If you want to run a 40W Actinic trap for 8 hours a night for 3 nights without access to a charger, the smallest battery you can use is: (3.3 x 24h) + 20% = 95Ah (or a lorry battery) !
Most peoples requirements will fall somewhere in between those two extreme examples. FOR DETAILS OF BATTERIES / CHARGERS I CURRENTLY SUPPLY - SEE HERE:
DON'T DISCHARGE BATTERIES MORE THAN 80%, or you may find they won't recover, or are difficult to recover. You can get chargers with a "recovery" facility to help recover over-discharged batteries. However, fully discharging can drain the battery beyond recovery and tends to invalidate the battery guarantee ! It's a bit like running your fuel tank dry on your car - just don't do it and expect the whole world to be rosy the next day !
SMART CHARGERS: There's also a problem with over-discharging your battery IF you have an electronic Smart charger which auto-detects between 6V and 12V. If you flatten your battery and try to recharge it with an auto-detecting smart charger, it may detect your 12V battery as being a 6V battery and only charge it up to 6V and then stop. To get past this problem, you need to connect your battery to another charging source (12V old type charger, or your car) to bring the battery voltage up above 9V, whereupon your so-called "Smart" charger will then correctly recognise the battery as 12V and charge it up to 12V. The other solution is NOT to over-discharge the battery in the first place. Easy said !
REMEMBER - Your battery capacity is always smaller then you think it is.
And if it's getting old and tired, it's MUCH smaller than you think it is.
BUY TWO batteries or more and swap them over.. one in use and one on charge. After all - if you had a hearing aid, you wouldn't just have one battery would you???
IF YOUR TRAP STAYS OUT DURING THE DAY - why not stick a solar charger onto the battery..... put a bit back in during the daytime. You can get some neat little 20W panels with charge controller.
AND FINALLY - Remember, just about all the "reasonably priced" Sealed Lead Acid batteries these days, are made in the same shack in China, so don't expect miracles unless you've paid a small fortune for your battery.
If I haven't put you completely off 12V portable moth trapping - then good luck !
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