View Full Version : Battery size requirement

Enfield Guy
15th September 2016, 12:18 PM

I trade at markets and have the standard gazebo arrangement. I have purchased a set of LED rope lights to provide lighting for the occasional night/ twilight markets I plan to attend. The rope light concerned is 12 metres long with 24 LED's per metre. Power consumption is quoted as "less than 12 Watts". I have had vastly different advice as to what size gel cell I need to run this rope light for 4 - 5 hrs. 9Ahr - 500 Ahr. Or $35.00 - over $500.00.

I would like the system to work but I don't want to over engineer it.

Can someone offer advice please.


15th September 2016, 12:47 PM
Assuming the LEDs operate from 12V, they would draw 1 Amp. A 1 AH battery will provide 1 Amp for 1 hr before the battery is completely drained.
I would aim for 2x required capacity. So a 10 AH battery would be sufficient. This will provide 1 Amp for 10 hrs before it needs recharging.
Something like this 12V 12Ah SLA Battery | Jaycar Electronics (http://www.jaycar.com.au/12v-12ah-sla-battery/p/SB2489).
You will of course need some means of recharging and some form of overcurrent protection wouldn't go astray.
A simpler option is one of these https://www.autobarn.com.au/powerwize-jump-starter-600amp-pjs600 Not too expensive and they have a 12V socket that is circuit breaker protected. Usually have a swith to turn the output on and off and come with a charger.

Enfield Guy
15th September 2016, 03:53 PM
Thank you sir

I have gone down a path similar to what you suggested. In my travels I saw a tiny little battery pack thing that also is a jump starter. Maybe 75mm x 30mm x 200mm. Very light weight and would be easy to store and carry. Claimed to be 14 Amp/Hr so would have done the job. Downside was price and the fact they don't come with an accessory outlet, although there is provision to plug one into it. If I had more coin I would have jumped at it. I'll see if I can find a link.

Thanks again

Enfield Guy
15th September 2016, 03:56 PM
Here you go. This is quite like the small one I spoke of. Mini Jumpstarter™ is a mulit-function Jumpstarter and POWER bank (http://www.minijumpstarter.com)


Big Shed
15th September 2016, 05:16 PM
Here's another one that would do the job, 17ah

SCA 12V Jump Starter - 4 Cylinder - Supercheap Auto (http://www.supercheapauto.com.au/Product/SCA-12V-Jump-Starter-4-Cylinder/395844)

15th September 2016, 08:19 PM
Working on the basis that you wish for the battery to have a long(ish) life, then drawing it down too far is not good for longevity.

With lead acid batteries, one can take them down to around 50% of maximum Depth of Discharge (DOD), which is the suggested maximum DOD for still maintaining a reasonable life span.

Your requirements are 12W, allow a bit of a fudge factor and use 15W draw. You mention 5 hours, so 15W x 5 = 75W drawn. If you need to hold to a DOD of no more than 50%, then you should aim for a battery with a 150W capacity when fully charged.

150W divided by 12 = 12.5A. Once again, allow for a bit of a fudge factor with a slightly bigger battery as performance and power holding capacity certainly diminishes with age, I would be looking for a 15A battery as a quite safe minimum. This should give you reasonable to excellent performance, a good lifespan, if not abused, and, be of reasonable cost.

Recently Aldi had a quite nice sealed lead acid battery on special, it was a 40A unit, their special price was $99.99; it was on Special September the 10th. I saw three in my local Aldi last Monday when I looked at stuff. I was very tempted, but didn’t succumb.


16th September 2016, 11:18 AM
I would just buy the cheapest car battery you can find, ie one from a small hatchback or similar. Keep it charged when not using and it will last 10 years or better. Melb 12V 330 CCA CAR Battery 38B19L R LS RS Lancer Mirage Mazda in VIC | eBay (http://www.ebay.com.au/itm/Melb-12V-330-CCA-CAR-BATTERY-38B19L-R-LS-RS-LANCER-Mirage-Mazda-/272172514623?hash=item3f5ebefd3f)

Sizewise, anything from a car is going to be overkill, but they are mass manufactured and you can get them cheap. The bonus is you wont need to worry about draining the battery either!

16th September 2016, 06:08 PM
Try one of these. We use them at work- fabulous.

AU 18000mAh CAR Vehicle Jump Starter Backup Power Pack Charger 600A Lipo Battery | eBay (http://www.ebay.com.au/itm/like/321951453385?lpid=107&ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F705-139619-5960-0%252F2%253Fmtid%253D1797%2526kwid%253D1%2526crlp%253D50030753137_573061%2526itemid%253D321951453385%2526targetid%253D100809153217%2526rpc%253D0.20%2526rpc_upld_id%253D78715%2526device%253Dt%2526mpre%253Dhttp%25253a%25252f%25252fwww.ebay.com.au%25252fitm%25252flike%25252f321951453385%25253flpid%25253d107%252526chn%25253Dps%2526adtype%253Dpla%2526googleloc%253D1000286%2526poi%253D%2526campaignid%253D622828744%2526adgroupid%253D9840971857%2526rlsatarget%253Dpla-100809153217%2526gclid%253DCIbFkNKpk88CFQNwvAodMNkO1A%2526srcrot%253D705-139619-5960-0%2526rvr_id%253D1094155995510&lpid=107&chn=ps&ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F705-139619-5960-0%252F2%253Fmtid%253D1797%2526kwid%253D1%2526crlp%253D50030753137_573061%2526itemid%253D321951453385%2526targetid%253D100809153217%2526rpc%253D0.20%2526rpc_upld_id%253D78715%2526device%253Dt%2526mpre%253Dhttp%25253a%25252f%25252fwww.ebay.com.au%25252fitm%25252flike%25252f321951453385%25253flpid%25253d107%252526chn%25253Dps%2526adtype%253Dpla%2526googleloc%253D1000286%2526poi%253D%2526campaignid%253D622828744%2526adgroupid%253D9840971857%2526rlsatarget%253Dpla-100809153217%2526gclid%253DCIbFkNKpk88CFQNwvAodMNkO1A%2526srcrot%253D705-139619-5960-0%2526rvr_id%253D1094155995510&ul_noapp=true)

Enfield Guy
16th September 2016, 06:47 PM
Yes Lappa, I saw those, brilliant. However budget didn't stretch that far.


17th September 2016, 08:48 PM
I operate a stand at the odd market that has a fair bit of LED lighting - 4 x 5W downlights illuminating the back board with all the prices, and two 7W downlights illuminating the front counter from above, as well as some Ikea fairy lights. Probably about 40W in total. I use a pair of Panasonic 12AH gel cells in parallel and they cope nicely with the average market, but there's one I do that goes for 6 hours, and the voltage starts to drop at about the 5.5 hour mark. I have another pair of the same batteries under the front counter to power an iPad and PayPal Here card reader, which draw far less current, so I just steal one of them to run the lights for the last hour.

For your application, I'd expect a single 12AH gel cell would be ideal.