How long is it safe to run off car battery?

[ShellShock]

How long do you think I can run my Celestron Nexstar SLT off my car battery without draining the battery so much that I cannot start the car and get home! (Assuming I do not have the car engine running whilst using the telescope).

[Dude_with_the_tube]

you will be better off by buying a jump starter in Maplins and use that for running your scope.

something like this will keep you running for hrs.http://www.maplin.co.uk/5-in-1-jump-starter-with-portable-power-224871

[badgerchap]

I wouldn't run it for too long - my car 'advises' me to only use the radio for an hour without running the engine. You could always just turn the engine over every half an hour or so just to make sure things are alright - if it struggles one time then you know it's time to pack up and go home. Or you could always take a spare battery in the boot just in case you push it too far?

[ShellShock]

I was thinking of getting a 7Ah Powertank, but I was wondering how long that would power the telescope for anyway? I was hoping to get away with just using the car battery. This would not be a regular thing, and probably would only be for a couple of hours.

[breezy]

Hi mate I use a 9ah power tank thingy from maplins which is fine for my needs, but if you are going to run other bits and bobs then there are several threads on here relating to leisure batteries( used in caravans and on boats) these are much heavier duty eg: 88 ah and will last for ages when properly looked after .

[davew]

If you can think of a problem then someone has come up with an answer !

http://www.amazon.co.uk/gp/product/B0000WQZOS/ref=pd_lpo_k2_dp_sr_3/278-7160289-0613509?pf_rd_m=A3P5ROKL5A1OLE&pf_rd_s=lpo-top-stripe&pf_rd_r=1HW5RKD4CM3TY6H5DNWW&pf_rd_t=201&pf_rd_p=103612307&pf_rd_i=B002BZI3FQ

Don't keep starting your car to check it. That's a very quick way of running the battery down.

Dave.

[Andymac79]

You could fit an additional battery with a split charger, maybe thats going a bit far though

[ollypenrice]

If it's just the scope you are running and not dew heaters I'd have expected it to be fine for days! I really don't see a little scope motor causing your car battery much trouble. Likewise the manual's advice on the radio sounds a bit off-beam to me. You can run a radio for weeks on a tiddling little AA battery. What can be the case with modern cars, though, is that if you have to have other electronics running in order to run the radio then those might drain the battery. Just compare the amp draw quoted for your scope with the ampere hours quoted for your car battery.

Certainly don't keep starting the car though. That will hammer the battery. For belt and braces could you park it on a slope?

Olly

[Carbon Brush]

Using a car battery is a bit dodgy to say the least.

When the car is new, the manufacturer is under pressure to fit the smallest battery he can get away with. It is easier to shoehorn under a tight bonnet. It saves a kilo or two on car weight, for fuel economy. It costs less than a bigger battery.

But, the manufacturer has to leave enough capacity to deal with leaving lights on, not starting first time, etc.

Lead acid batteries degrade with time, regardless of how well you look after them.

So moving on a year or two.

Maybe when the car (battery) was new, that time you left interior light on all night wasn't an issue, but now it might be.

As a good example. Recently my car of 7 years started perfectly every day, despite the cold and snow.

One evening I spent less than an hour fiddling with the radio and one interior light on.

This consumed 2 to 3Ah of battery capacity.

Next morning. No go.

The battery had lost capacity. But I had not realised because it still gave the high current for starting.

Being of German origin, it always starts first time.

I now have a battery that is no doubt good for scope use. Not the 36Ah on the label, maybe half or one third of that.

On to 2/3/4/5 year guranteed batteries. They are all the same. You just pay extra for the increased risk of failure with time.

I have seen them coming off the manufacture line. There is no difference.

But, if you bought a Morris Minor, it would have a starting handle. Provided you had enough battery charge remaining to run the ignition coil for a minute or two, you could run your astro kit all night!

[ShellShock]

Yes I would just be running the telescope motor, and it is only a light weight mount (Celestron Nexstar 127 SLT) so I can't see it drawing much power. One thing though, in order to switch on the cigar lighter socket, I do have to activate the ignition; this does not start the engine but it does switch on the car's electronics, e.g., so the radio, fans, heater circuits are live, and some of the little lights on the dash come on. The Car Battery Monitor looks interesting.

Thanks everyone!

[badgerchap]

....... You can run a radio for weeks on a tiddling little AA battery. What can be the case with modern cars, though, is that if you have to have other electronics running in order to run the radio then those might drain the battery.

Yes, that's the problem with mine. Screen comes on, all kinds of lights....Yuck. Power hungry and there's normally just rubbish on most stations anyway!

[M4lcs67]

Yeah. Why run the risk of flattening your car battery?. I use one of the Maplin 3 in 1 powertanks to run my 127 SLT as mentioned. It works a treat. Just remember to always keep it topped up with power, even if you don't actually use it for a while. Never ever let the power fully drain out of it otherwise you will wreck the cells in the powertank. You will certainly get a full evenings observing out of one charge. Just don't forget to plug the charger in when you come back inside.

[ShellShock]

The Maplin charger looks like a much better deal than a powertank, it is £40 cheaper than the equivalent powertank. I think the Maplin charger also has a cigar lighter socket?