Running garage lights on a car battery

[HawkEye244]

I have four 17W floresant lights. This means I will need 70 watts of power.

So I get a 100W or 150 W Inverter. Connect that to the car battery then just plug the lights into the Inverter?

what you need to remember is 70w at 240v is 20 times the draw at 12v
so 20 times 70 is 1400w which =6 amps

so you need to work out the amp hour of your battery so if your battery is 40 anp hour[40ah] you will probably get 5 or 6hrs run time from a full battery allowing for a slight power loss in the conversion

So this is if I use a car battery? Will the AH of the car battery be visible when I buy it? Are there different powers of car battery? Also, is this the best option considering I won't be able to recharge it?... as far as I know

 

[ericmark]

Seems a few things missing.
1) A car battery can give very high amps and if not fused fire can result.
2) A battery connected to inverters of any type either built into florescent lamp or stand alone need correct polarity fuse may help if mistakes are made.
3) A lead acid battery can be made in different ways and to get the high amps required to start a car the active material is very open and deep cycling will cause it to drop off the plates you will be lucky for it to last 6 months. However a traction battery will not give high amps because of the way the active material is held but will last 5 years or more. A leisure battery is half way between the two and they can all look the same from the outside.
4) Lead acid batteries do not like being left flat and should be recharged every day and never left flat for longer than a week or the sulphur will set hard and they will not recharge.
5) Alkaline batteries can be left in flat state and nickel iron batteries are always stored flat, Nickel cadmium are the same.

There are battery packs now available with carrying handle and charger built in and leak proof these would seem good option to carry back to charge after each use.

Charging is another problem the trickle charger is likely to cause the battery to gas and with sealed batteries this will ruin them. Float chargers are better for battery but take a long time to charge them fully around 24 hours. Traction battery chargers use a double stage with a constant current until the battery reaches a pre determined voltage which will represent around 80% and then a trickle charge for set time after which they switch off and every round again the battery requires an equalising charge. Some will switch to float charge but most switch to trickle. As a result the battery is matched to the charger.

Even Nickel cadmium battery chargers can be complex.
a) Simple trickle charge will normally take 16 hours
b) Temperature sensor built into battery which will open circuit charge terminals when hot so telling charger fully charged theory is when battery is discharged the power is converted into chemical energy but once charged it will be turned into heat energy which is handy to know so if you feel battery and it is warm then likely it is fully charged.
c) It measures time and after set time periods it tests battery voltage if the voltage has dropped it stops charging as the voltage curve of a Nickel cadmium battery on charge reaches a peak and then drops. This is expensive method and normally used on things like two way radios which will be charged every day but may have different amounts of charge left. Also some either every so many charges or by pressing button will discharge battery before charging to reduce chemical memory.

As you can see not as straight forward as it first looks.

Eric

 

[ban-all-sheds]

so you need to work out the amp hour of your battery so if your battery is 40 anp hour[40ah] you will probably get 5 or 6hrs run time from a full battery allowing for a slight power loss in the conversion

No - amp-hour figures indicate, vaguely, the stored energy in the battery. More useful is the Reserve Capacity rating, which is the number of minutes that it will deliver (when 25A before the voltage drops to 10.5V, at which point lights would be noticeably dim. A good inverter might keep going for a bit longer, but the RC time is unlikely to equate to the Ah rating.

 

[ericmark]

so you need to work out the amp hour of your battery so if your battery is 40 anp hour[40ah] you will probably get 5 or 6hrs run time from a full battery allowing for a slight power loss in the conversion

No - amp-hour figures indicate, vaguely, the stored energy in the battery. More useful is the Reserve Capacity rating, which is the number of minutes that it will deliver (when 25A before the voltage drops to 10.5V, at which point lights would be noticeably dim. A good inverter might keep going for a bit longer, but the RC time is unlikely to equate to the Ah rating.

Some "Car" batteries may have a "Reserve Capacity rating" but traction and and leisure batteries with have AH rating normally a 10 and 20 hour rate as the slower you draw power the better the battery will last. And if you understand the difference between battery types you would not use a "Car" battery for standby lighting except if using old batteries no longer any good for a car as it will destroy the battery in a very short time and invalidate any guarantee.

 

[rebuke]

what you need to remember is 70w at 240v is 20 times the draw at 12v
so 20 times 70 is 1400w which =6 amps

You are right in that it's about 6A at 12V, however the wattage doesn't change, it's still 70W. At a simple level (ignoring things like power factors etc), P = IV (i.e. Power (W) = Current (A) * Voltage (V)), which we can rearrange to get I = P / V. So 70W at 240V gives us a current of 70 / 240 = 0.3A, but at 12V, we get a current of 70 / 12 = 5.8A...

 

[HawkEye244]

What is the most cost effective solution to this? I am prepared to take a battery in and out the garage only using it when I need it. I would prefer if it has a moderate amount of battery life (a few hours at least) before it runs out and for obvious reasons the least amount of recharge time would be handy. Something that will hold its current.

What do I do?

 

[big-all]

blimey thats me well and trully told off

as my addy says i am still learning
thanks for correcting me chaps

"ericmac"

i did mention a 10 amp fuse on the 12v side it sits in a holder affixed to the purpose built shelf the battery sits on

can someone tell me if i have given any information thats dangerous!!!
i genuinly want to know so i can correct it and my though prosseses

 

[electronicsuk]

What is the most cost effective solution to this? I am prepared to take a battery in and out the garage only using it when I need it. I would prefer if it has a moderate amount of battery life (a few hours at least) before it runs out and for obvious reasons the least amount of recharge time would be handy. Something that will hold its current.

Running off your existing generator would be the most cost-effective solution. The next step from that is a good leisure battery (£50, perhaps), associated fuses, wiring, battery clips, sundries (let's say £20) and then as many 12v fluorescent fittings as required. I seem to remember CPC had some in one of their sales brochures a while ago, around the £10 mark at the time, although this was probably a special offer price.

 

[HawkEye244]

What is the most cost effective solution to this? I am prepared to take a battery in and out the garage only using it when I need it. I would prefer if it has a moderate amount of battery life (a few hours at least) before it runs out and for obvious reasons the least amount of recharge time would be handy. Something that will hold its current.

Running off your existing generator would be the most cost-effective solution. The next step from that is a good leisure battery (£50, perhaps), associated fuses, wiring, battery clips, sundries (let's say £20) and then as many 12v fluorescent fittings as required. I seem to remember CPC had some in one of their sales brochures a while ago, around the £10 mark at the time, although this was probably a special offer price.

Well I type the term 'Leisure batteries' into google and get alot of different stuff. Do you recommend anything in particular? Where would I buy all the assesories?, preferably in a bundle.

 

[ericmark]

To big-all nothing really wrong with your set up. I would not use inverter connected to tungsten only because it uses more power than discharge lighting.
At one time you could get 2D lamps in 12 and 24 volt versions at 28 watt these were really good.
But more likely cost wise 12 volt caravan lights best option.
Before re-training as a mains electrician I was an auto electrician hence I had to know about batteries.
Returning to HawkEye244 it would depend on what you want to spend of course and how much light but if 4 x 18W florescent lamps would give you enough power than a 60 AH battery will run them for 10 hours and if you go to a caravan shop you can buy special carrying box with plugs and sockets to connect with ease. Maybe once you have seen one you can get a plastic bread bin to do same job and DIY. As to charger caravan shop most likely but look for word “Regulated” cheap option is a CB power supply.
If you want to DIY further I can give you regulation circuit either as add on to standard battery charger or using a transformer but I found cheapest was to build my own over charge eliminator basically a 2N3055 transistor and large bulb together with a power op-amp and voltage reg chip as the voltage reached 13.4 it started to light bulb both showing it was charged and getting rid of any excess voltage.
Again how fast do you need to re-charge a 1 amp 7812 voltage reg and red LED will give up to 1 amp at 13.2 volts very cheap but would take around 100 hours from flat with 60 amp hour battery.
With some lamps you can get twin or more tubes allowing you to select how bright or how long they will last.
But first have a look around a caravan shop. And see what is available. Unless you know someone on the buses the double 20 watt units they use will also power a 40 watt tube these are A1 but to buy new a bit expensive. I converted 6 standard florescent units to take the 24 volt versions in a farm house on the Falklands they were great he used 2 foot tubes at 40W each as he thought carrying 4 foot tubes over the camp (Falklands name for countryside) they would get broken.

 

[HawkEye244]

So a 60AH Regulated battery? Do all batteries last about ten hours?

 

[big-all]

thanks ericmark for your feedback

he actualy used low energy light bulbs[3x18w]
the reason for 230 over 12v was the ability to run a 70w telly and 3 bulbs
and a 12w soldering iron as an ideal choice
he felt the cost of 12v lighting would be more expensive than 230 v
because he already wanted 230v for a telly

 

[maltaron]

I note the OP has no knowledge regarding batteries invertors etc. I would make the point that in the wrong hands batteries are more dangerous than mains power. If you've ever seen a car battery explode through incorrect charging conditions you will know what I mean and a short or wrong polarity connection can be lethal. Now the warnings are finished the advice re batteries is to use either leisure batteries or sealed lead acid and charge with a constant voltage charger, and this must be housed in ventilated enclosure outside. Before retiring I provided outdoor public address systems for fetes etc and ran the whole systems on battery power so I have long experience of this. I would suggest that it will be far cheaper to use the generator.

 

[ericmark]

I do agree with maltaron I note he wants a "Regulated Battery" which is not what I said needs a regulated charger to recharge the battery.
And yes worse I saw was on a 966 digger loader where batteries were under seat no cab in Sahara so hot over charging two 140Ah batteries driver lit a fag and dropped match seat and him left digger like ejector seat lucky landed in sand and digger also stalled in sand heap.
I had just arrived with new alternator and was able to empty a carboy of distilled water over him to wash off acid.
Very lucky man although don't think he thought that!
In UK not seen many blow up but even then working in BT building and needed to use power tools in battery room all windows open and gas meter placed on top of ladder. Boss came in and told off guy saying gas meter should be on the floor? After referring to Air ships did get sense into Boss but shows how easy to make mistakes. I also worried him as he said there was not real danger so asked him if he had ever heard of hydrogen bomb. I never did point out that we were not splitting atom!
But yes they are dangerous and "Sealed" batteries are only sealed to stop acid getting out if tipped over they will still release hydrogen gas which will go up so smoking is a no no.
There are some battery packs with built in charger designed to jump start cars which have cig lighter socket built in which would mean the whole unit is self contained seems good way to transport power.
But caravan options have a better battery for job even if not as neat. So I would look at caravan battery pack.
And as long as not over charged the danger is quite low. Except for a batch of wagon batteries which were made with undersized posts when manufacture was saving on lead it is unusual for batteries to explode when power is being taken from them. Most explode when being over charged.
Eric
PS the time a battery will last will depend on how big it is in AH and how much you are using question like asking length of piece of string.
Simple maths

 

[maltaron]

Just a follow up the worst I saw was a 120ah digger battery used to power large timing displays. The load was connected with no switch and the resulting spark split the battery apart, luckily the acid all went to the floor and the operator narrowly escaped serious burns.