Which power supply for a mobile astronomer?

[Delboy_Hog]

Just now, Stu said:

The Tracers are expensive but worthwhile in my experience. They hold their charge for a long time without needing recharging, and just seem to deliver to their rated capacity very well. I have a 110 Ah leisure battery which rarely gets used now, mainly because it is so heavy and needs regular charging.

Thanks Stu, that's helpful to know.  It certainly seems like the most straightforward option...

I might opt for a Tracer to get me sorted straight away, and work on customising my own set up over the coming weeks / months for when my power needs grow!  There's a few little astro-kit projects I'm thinking about, and they all require a certain degree of up-skilling on my part, so I'm quite looking forward to it all!

[Delboy_Hog]

Thanks all - you guys are so helpful!

[RayD]

The Tracer LiPo and LiFePO4 units are really good, and as Stu says they do come at a price, but out of all of this type of unit, they are the one to get if you want them for the long term.

One benefit of the LiPo units is that they deliver a pretty flat supply, so give you pretty much full power all the time, then simply shut off.  The one down side is also just this, as without keeping a very close eye on the power meter, you just won't know it's running low.

If I was in the market for a new LiFePO4 bank, I'd be getting a Tracer one.

[dannybgoode]

One thing to bear in mind about LiPo's is they are very fast discharge batteries. The Candoia rating you see on them is their optimum discharge rate and is a multiple of their capacity. 

So a 1000mAh 20C LiPo has an optimum discharge rate of 20Ah. They get grumpy and their lifespan shortened if discharged slowly. 

Note also be careful how you charge them. Get it wrong and it can have catastrophic consequences. 

LiFe batteries address these shortcomings and are very much slower discharge batteries and less volatile. 

Note I also fly (well crash) RC electric helicopters and LiPo's are where they're at because of their extraordinary discharge capabilities. Some of the bigger heli's have 10-15kW of grunt!

I personally would not use LiPo's for this application for these reasons. LiFe's definitely yes I would. 

[cjdawson]

I've been looking at generators for my Caravan.  From the feedback that I've been seeing it looks like they are frowned upon by Caravaners as they're too noisy.   Of course, most sites have electric hookup, which is powerful enough to run a well equipped caravan and astro setup.   The ones that don't have electric hook up on the other hand, are a huge problem - the generator would be great.  However, they'd be too noisy to run at night, and as I said, in the day people get annoyed.

[Davey-T]

7 minutes ago, cjdawson said:

I've been looking at generators for my Caravan.  From the feedback that I've been seeing it looks like they are frowned upon by Caravaners as they're too noisy.   Of course, most sites have electric hookup, which is powerful enough to run a well equipped caravan and astro setup.   The ones that don't have electric hook up on the other hand, are a huge problem - the generator would be great.  However, they'd be too noisy to run at night, and as I said, in the day people get annoyed.

Many motor homes come with "silent" generators nowadays, but they're not cheap, there are also gas powered ones so can be run without needing to carry a can of petrol.

Dave

[RayD]

I have a little Honda EU20i 2kw generator which is brilliant.  It's been converted so will run on Propane or petrol, although you have to run the petrol completely out before running on gas, and whilst it is only 52dB(a), so technically what would be classed as super silent, you still wouldn't want it outside your tent in the still of night.

[JOC]

FWIW I'm trying a Maplin 5 in 1 17 AmpHr sort of car jump-starter leisure charging type box.  I got it in a bashed box from the Maplin Outlet site on ebay for £50.  Now they don't get a good write up which I did consider, but it looks the part - weighs enough to actually contain a 17 AmpHr battery and has 2 X 12 V cigarette adaper outlets, an inverter 3 pin socket, a compressor, a white light and the usual car jump start connections.  Reading above I think I'll have to calendar a checking and re-charging schedule, but I got it last week and have used it once - I was out for about 3 hours powering the Goto and driving the 'scope mount' and it hardly put a dent in a full charge. Clearly I can't comment on ultimate longevity, but at the moment I'm pleased enough with what I've seen for the cash spent and I'm OK if the car doesn't start one morning!

[cjdawson]

2 hours ago, JOC said:

FWIW I'm trying a Maplin 5 in 1 17 AmpHr sort of car jump-starter leisure charging type box.  I got it in a bashed box from the Maplin Outlet site on ebay for £50.  Now they don't get a good write up which I did consider, but it looks the part - weighs enough to actually contain a 17 AmpHr battery and has 2 X 12 V cigarette adaper outlets, an inverter 3 pin socket, a compressor, a white light and the usual car jump start connections.  Reading above I think I'll have to calendar a checking and re-charging schedule, but I got it last week and have used it once - I was out for about 3 hours powering the Goto and driving the 'scope mount' and it hardly put a dent in a full charge. Clearly I can't comment on ultimate longevity, but at the moment I'm pleased enough with what I've seen for the cash spent and I'm OK if the car doesn't start one morning!

I've got experience with the 17Amp lead acid batteries.  For your application - powering just the mount, maybe with a due heater, it will work great for a few years.  Just make sure to keep the charge up on the battery.

When it gets old, what is likely to happen is that the charge will appear to be fine, then all of a sudden, it will drop from loads of charge to nothing at all.     I wouldn't worry about this until it happens and it might not happen for several years.  Especially if you look after your battery well. (I didn't and it still lasted a few years)

[JOC]

cjdawson - that's excellent to know, many thanks for taking the time to post, I am even more happy with it now!

[RayD]

The biggest issue with shallow cycle lead acid batteries, or car starter batteries as they are commonly known, is that they are simply not designed to be discharged........at all.  They are designed to supply very high current for very short periods, but need to be immediately recharged.  If they discharge to levels that a deep cycle battery is designed to (80% DoD) then they will very quickly become damaged and stop holding a charge.  Also consider that most shallow cycle batteries (and pretty much ALL of the cheaper ones) are wet cell open type batteries which leak if tipped.  SLA's don't leak, so are better if you're transporting them.

Now the above noted, the reason some people get many years out of starter batteries is simply that they have far bigger than their needs and don't deplete them to any significant level.  If people get a small one, run loads of things from it, so are often "flattening" the battery, then it won't last very long at all.  In these instance shallow cycle are much better as they are cyclic, so are specifically designed to take a heavy discharge without damage.

[Bagnaj97]

I built myself a battery box in the last couple of weeks, I used crimped connectors (mostly spade terminals) for all the connections, no soldering required. I've had a dig through my ebay history and these are the exact parts I used:

The Basics

6mm red and black wire to go from battery to fusebox, and terminal block back to battery. 1m of each should be more than enough - http://www.ebay.co.uk/itm/321407195097

1.5mm red and black wire for the individual circuits. Order more than you think you'll need, experience tells me it's better to have spare than wait for a second order... - http://www.ebay.co.uk/itm/171504064730

30a circuit breaker - http://www.ebay.co.uk/itm/131858062863

Blade fuse box. 6mm red wire from battery+ goes to the main terminal on this with the above breaker inline near the battery end - http://www.ebay.co.uk/itm/222258979277

12v cigar sockets - http://www.ebay.co.uk/itm/371789007180

Terminal block. Connect your individual circuits into this, and the 6mm black wire back to battery-. - http://www.screwfix.com/p/5-way-sp-100a-service-connector-block-25mm/82608

A bunch of crimp terminals - http://www.ebay.co.uk/itm/371581270051

Ratchet crimping tool - http://www.screwfix.com/p/ratchet-crimping-tool-1-0-10mm/96561

You'll also need wire cutters/strippers, battery terminals, battery, appropriate blade fuses for the fuse box and a box to put it all in!

I wouldn't fuse the individual circuits higher than 10a without using thicker wire. If you draw more than 30a total you'll trip the main breaker, but that should be plenty. If you use a bigger breaker, use thicker wire to the battery.

 

Optional parts:

Switches. You don't have to use them, you could leave the sockets live. You could use non-LED switches instead. - http://www.ebay.co.uk/itm/141725682546

Combined voltmeter and 2x 2.4a USB outputs. USB power and battery voltage monitoring in a single device, very useful! - http://www.ebay.co.uk/itm/262500180144

PWM controllers for dew strip control. There are other options, but these have the dial on a flying lead which makes mounting them easier. - http://www.ebay.co.uk/itm/181925173017

Phono/RCA connectors. Standard connector used for dew strips - http://www.ebay.co.uk/itm/321924246761

Heatshrink tubing and electrical tape is handy to have, just in case!

 

Top panel. Layout was constrained by reinforcing plastic below, and I didn't measure anything:

 

All wired up, room left around battery for insulation. I've since added a bit of plastic under the battery hold-down to cover and insulate the battery terminals:

 

Wiring detail:

[Delboy_Hog]

Wow Bagnaj, that's impressive!

 

Spending a bit of time this weekend looking over all the options and making the decision about how to power my set up.  It looks like we might start to see some breaks in this awful cloud we've been having after the weekend, so I want to make sure I'm in a position to make the most of it!

 

Thanks again for sharing all of your thoughts, advice and experiences!

[Waldemar]

Yes, it is a nice job, though it also means a lot of wiring up to the mount...
I am in favour of just one wire up and a power hub on top or underneath the lelescope on the dovetail. Velcro works great to attach it.