Portable battery packs.

[cyborg421]

Hi All,

Had probably the best summer night ever for observing yesterday. Only one problem that my battery pack started to give up the ghost after about 2.5 hrs.

I have this one.

http://www.maplin.co...t=Jump Starters

I think I was under the impression when I bought it that it was 17.5Ah whereas in fact listing says it is 7.5Ah. My Sw 250 is quite a heavy beast and I think I need a battery with a higher rating.

Recommendations please.

Thanks

Simon

[Bizibilder]

Ideally you need a leisure battery - as used by the caravan and boating people. These seem expensive but will outlast any jumpstarter! You will also need a charger/conditioner which, of course, adds to the expense. Bad news over.

To work out what capacity you need add up the kit you are using (really the kit you are likely to use as you want to be future proof). In my case: 2A for the mount (in fast slew, normally only 1A to track), 3.5A for the laptop and maybe 3A spare for dew heaters etc. Total 7.5-8A. Multiply by the number of hours a long session may be - 6 hours in my case so: 6x8=48Ah (Amp Hours). You should have a bit in reserve, so double that to 96Ah. A battery of between 75-100 Ah capacity should do the trick. I use a 75Ah and have never had any problems over three years of use.

Leisure battery: Designed for continuous current draw over time.

Car / Jump starter battery: Designed for one big Woomph!! and a recharge.

[cyborg421]

Thanks Roger.

Good news - I already have a charger conditioner.

Have you got a link to the kind of leisure battery you are talking about?

Do you connect it unfused to the scope?

Simon

[Merlin66]

I found the leisure battery an OK solution... but it's very heavy to lug around.

I ended up with a couple of 20Ah gel cell batteries and a triple stage electronic charger.

These are now almost six years old and still function at 100%

A good long term investment.

Look for golf buggy batteries etc

(How many "battery packs" out there of similar age???)

[Bizibilder]

I bought from these folks: http://www.tayna.co.uk/Leisure-Batteries-C45.html Several members of SGL have used them, I believe. My own experience was that they are sensibly priced and delivery was quick with no problems (sound like a salesman!!). I use a commercial battery box which is not fused (naughty me!) - you can buy fuse holders and cigarette sockets from: http://stores.ebay.co.uk/towzatronics - I've used them a few times now, as have others.

One design for a box is here: http://stargazerslounge.com/topic/57620-105ah-powertank/ and there is a thread runnung at the moment with a decent wiring diagram here: http://stargazerslounge.com/topic/154685-power-tank-build-help/ Hope this helps.

[cyborg421]

Thanks for the replies guys. I think on a weight basis it seems that the golf buggy batteries seem to be the one to go for.

I am assuming it is 12V with a positive and negative terminal.

I am still unsure about wire/wiring for fuses. I assume the fuse goes inline. What value fuse would be sensible or can you buy a wire suitable prebuilt with the fuse?

Thanks

Simon

[swamp thing]

Hi Simon

What are you like at car electrics?

I ask this because if I needed to run a Goto or some other electric reliant mount I would hardwire a split charge system into the cars electrical system. This would give you the possibility to have a large leisure battery( permenantly charged )in your place of choice on the vehicle. We use this system when fitting electric winches to overland vehicles.

Most campers have this sort of arrangement. It also means if you do flatten the battery, it has no effect on the vehicles main starting battery.

[cyborg421]

Hi Steve,

I'm not a complete nincompoop but I don't think I would fancy fiddling with the car electrics. I don't tend to use dew heater etc so my main power drain is the goto of the scope. I was just finding that 7.5Ah isn't enough for that over a 3-4 hour observing session.

Simon