Batteries (Yet again) for a goto dob.

[The_bluester (Paul)]

Having bought an 8" goto dob for my son I will be wanting to set it up for easy use for him. Assuming perhaps a heater for the eyepiece, what sort of battery capacity are people getting full nights use out of?

I am hoping to be able to use an SLA physically small enough to mount inside the base in front of the azimuth motor as it will be one less thing to trip over. I can hopefully test it soon for myself but how many amps do these things need for slews?

I am working on the assumption that he will be likely to hop around with heaps of slews over a night at least for the first year or so, so a bit of extra capacity would probably be wise compared to a set and forget user who observes targets for extended periods.

[rrussell1962]

I recently bought a Powertech portable power centre from Jaycar which I use with all my scopes (Obsession 18" and ServoCat, Nexstar 8SE, Vixen GPD with Skysensor 2000PC). Lithium ion, weighs not a lot, does for a whole evening slewing and eyepiece dew heater, 42 amp hours, 155 watt hours. Very quick recharge. Not exactly cheap but perfect for what I need. Added a couple of pictures with CD case for scale.

[The_bluester (Paul)]

I will have to go get myself some proper measurements. That would have to be close to tucking in front of the OTA of the dob when it is vertical.

A pity it would not cope with the main heater on my SCT or I would look at two of them. You can't get away without one outside warmer weather and the heater for a C925 pulls a couple of amps by itself.

[Merlin66 (Ken)]

Whoooo
A hellava price, but very very impressive!!!!
Only 1.6Kg for a 42Ah battery system.....I like it!

[rrussell1962]

I suspect the 42Ah is measured at the USB output, but even so say 17Ah at 12V, maybe 10 useable Ah at 12V without running it too low makes it very convenient for what I need.

[xelasnave]

Anyone run one of these to consistently take out 10 amps?
I assume you can near drain these batteries?
Alex

[rrussell1962]

I certainly have not Alex. I don't do AP so just use it for the mount and eyepiece dew heater turned up just as high as it needs to be. I have a heated dew shield for the Nexstar but have never needed to plug it in. The weight, quick recharge time and convenience made it appeal to me. Also keeps the iPad charged. Three 12v and 3 USB outputs. But yes, pulling 10 amps at 12 volts from a 155 Wh supply will not last long!

[Allan_L (Allan)]

I used to run 12" DOB GoTo and three dew heaters (through an Orion Dew Zapper controller) and a small fan.
These were not all running together full blast all the time.
But I did get through each night's observing on one battery.
Maybe not ALL night, but till way after midnight.
18aH deep cycle.
Like this one from Jaycar $80

It fits on the outside rim of the mount base

[Merlin66 (Ken)]

Yeah, I still have and use two 20Ah "golf buggy" batteries (with a triple stage charger) - these are now over 11 years old and still going strong......

[Steffen]

Originally Posted by rrussell1962

I suspect the 42Ah is measured at the USB output, but even so say 17Ah at 12V, maybe 10 useable Ah at 12V without running it too low makes it very convenient for what I need.

The Jaycar site doesn't make it clear, but the user manual that can be downloaded from there spells it out: it's 42Ah at cell voltage – 3.7V. Hence the 155Wh capacity. This compares to lead-acid 12-13Ah, but considering that you can use almost all of that charge (rather than just over half), this battery is probably comparable to a 20Ah lead-acid battery.

The direct solar charging ability is a nice touch. Without knowing the lifespan (I'm guessing 500 full recharge cycles) it's difficult to judge the value proposition. The price does seem to be on the high side, assuming that the device probably contains less than $100 worth of 18650 cells, or similar.

[rrussell1962]

Totally agree Steffen, it's very expensive for what it is. But after many years I don't want equipment hassles any more. I just want something that works easily out of the box! Anyway - a clear night in Brisbane so off to the planets!

[xelasnave]

So I had it right more or less. I could not work out how it was 42 amps at 12vlt.
As to price thats not bad. Little things like leads connections etc that take it past a straight battery purchase.
I use 100 amp and another smaller which I dont know its rating but maybe 70 amps and the lap top drains one battery in about five hoirs ...well the inverter shuts down and that is good enough for me. I run the mount only off the 100 amp hour which wont draw it down to far. Recharge next day with a neat 120 watt panel ...which although seemingly expensive had little features that you often have to add like regulator good leads with good bulldog clips or terminal ending..with good fittungs to connect I cant remember but its the best one...all those little things you will need but cost heaps...and stand and good bag...I try to be very gentle with batteries 10 % is my goal discharge.
If I get a cooled camera I will get maybe 150 amp hour just for it...thats big so probably two 75 ah ...you can never have too many batteries.
Alex

[AstroJunk (Jonathan)]

This is the inside of my 20".

The 7AH battery and above it onboard 1600ma Projecta battery charger keeps me running very nicely with full goto and a full complement of dew heaters.

Don't expect to pull an all nighter, but it will easily manage six hours or so without the need to resort to larger external power solutions. It sits plugged in when inside the house, the charger is designed to trickle charge motorcycle sized batteries and the like so works a treat.

[Steffen]

Originally Posted by rrussell1962

Totally agree Steffen, it's very expensive for what it is. But after many years I don't want equipment hassles any more. I just want something that works easily out of the box! Anyway - a clear night in Brisbane so off to the planets!

It turns out that LiFePO4 batteries of similar capacity are about the same price or even more. They would be the alternative light-weight no-hassle option. Of course they don't include an AC inverter or solar charging ability.