Hi Stefan, The number of amps is irrelevant to low current users like us, it is just the number of amps that the unit can put out at a given moment for high current usage such as car starter motors.
What matters is the number of ampere/hours, which is analogous to how
much petrol a tank holds, the bigger the tank the further it will drive the car. A 900 amp unit is usually around 17amp/hrs, meaning that it will supply 1 amp for 17hrs, or 2 amps for 8.5 hrs etc: The amount of petrol in the tank does not matter much for jump starters, as they are designed for high current output for as long as it takes the engine to start. In light of this the amp/hr rating doesn't increase a lot as the max current rises.
An 1100amp unit usually has a rating of 19amp/hrs, a1300 amp unit
21amp/hrs, and so on. A small car battery will give far more bang for your buck; for instance a 350 cranking amps car battery will give at least 60amp/hrs,[depending on model and price] and can be got from Repco for about $95.
raymo
If your running a mount all night, and drawing power for heater or other equipment like camera power, etc then a deep cycle camper type battery is a better choice. Those 900amp jump packs don't last long whn your asking it to run the mount and heaters, I know I had to 'recycle' my old one. I pulled it apart and found a simple 17AH battery, not much better than home alarm battery.
I was able to obtain these values, not sure if they are right though.
HEQ5 Pro: 12VDC, 2Amp
Dew band (Kendrick 7"-8"): 20W, 1.6Amp
24 Watts + 20 Watts = 44 Watts
and comparing it with the SCA Jump Start charts...
Yellow 900 Amp Starter: Just over 2.5 hours
Purple 1900 Amp Starter: Just over 5 hours
Am I better off using the Purple one just for the telescope/mount and the yellow for the Dew band or getting something like the Jaycar one and running everything from that?
Gel batteries generally last a bit longer than car batteries when used for
this type of application, allow say 30% longer. A 38a/h gel at $219 gives
about 50-55% of the capacity of the car battery that I mentioned for well
over double the price. Allowing for the longer life of the gel battery, that still makes the gel battery around three times less value for money. Add to that that if doing a fair bit of slewing of the mount, and running the dew heater, the gel battery would barely last for a long session.
People always over think this power supply issue. I have been using car batteries for almost 40 years, and never had a problem.
raymo
Hi Stefan , Raymo's explanation summons it all up and your maths is correct.
I believe you would be better off with with the SCA 1900, it is rated at 38 Amp/Hr same as the Jaycar battery, so should last almost as long maybe a bit less as its a lead acid in the sca, as Raymo explained.
Also the battery wont come with any cables / jacks or outlets and you will need a charger for it.
Plus you should have enough juice to jump your car at the end of the night if required
The Jaycar unit quotes is a true "Deep Cycle" battery, and hence will/should survive the occasional over discharge, whereas the std SLA and car batteries will die quickly in that scenario.
Easy to do when connected to a telescope etc.
The Synscan mounts beep at you when the voltage is too low, so it should
be easy to avoid that problem, apart from which if you did stuff up your car battery, you could buy
another one and still be ahead financially.
raymo
Last edited by raymo; 01-03-2016 at 04:11 PM.
Reason: more text
The Synscan mounts beep at you when the voltage is too low,
Does that happen when the handset isnt in use????
I know the switch blinks on low voltage, ......but if yr not looking :-(
Another interesting alternative someone mentioned is getting used golf cart batteries. Some places change em over after a set time and many are still quite good for scopes.
Stefan, have a look on Ebay. There are plenty of deep cycle gel cell batteries or even better, AGM deep cycle batteries, for much less money than Jaycar charge.
This is my home made power supply using an 18 Ah AGM battery-the design could be adapted for larger batteries if need be. I have included storage for various tools, fuses etc.
I am a complete nong with electrics so I bought the battery box too...Its great comes with 2 ciggie lighter spots an Anderson plug...whatever that is.. and a LED voltage display. Was delivered to my door fully charged. They have sales every now and then, I think I paid $320 delivered for the lot, don't know if thats expensive or not but this will last me for days.
Then I bought a 7 stage charger from one of those car places, can't remember which one. Now all I need is a Solar charging set up and I'm done.
Andrew, It just occurred to me that I changed to the new V.4 hand
controller a while back, and can't remember if the mount beeped with the old V.3 one. I so rarely let the voltage drop that low that I now don't know if it did beep. Maybe the beep is a new function with the V.4.
I never use it without the H/C, so I have no idea whether it would beep
without it.
raymo
I know the SCA unit itself beeps when the voltage is low.
I have the SCA 1200
For $120 it seems like a bargain for the SCA 1900 and you wont need to get a charger or cigarette outlet sockets for it.
I feel like a total Richardhead; I just remembered that I
was using my jumpstarter when the low voltage beeping happened. I had assumed it was coming from the mount.
I plead senility.
raymo
Last edited by raymo; 01-03-2016 at 09:35 PM.
Reason: more text
Stefan thanks for the heads up on the SCA sale. I've also been using the 900 amp unit with the same issues when I start using dew straps etc. So I dropped into Supercheap today and picked up the 1900 amp version. I had been contemplating a more expensive power solution, but for $120 I've now got 2 units (900+1900) and pretty sure I'll be covered. Bonus: the 1900amp unit also includes a powered USB port which the 900 doesn't.
Thanks for the replies, good to see many different solutions that people use.
I have a mate who is a gun at anything electrical who is making me a custom battery kit. Once I get it I will be more than happy to post up some pictures and a description.
Stefan thanks for the heads up on the SCA sale. I've also been using the 900 amp unit with the same issues when I start using dew straps etc. So I dropped into Supercheap today and picked up the 1900 amp version. I had been contemplating a more expensive power solution, but for $120 I've now got 2 units (900+1900) and pretty sure I'll be covered. Bonus: the 1900amp unit also includes a powered USB port which the 900 doesn't.
No worries!
That was my initial plan but I am not getting a custom made kit done. That SCA is fantastic for the price.
I
