Building a power tank

[Simon Dunsmore]

Hi folks,

Bank holiday project looming on the horizon.

I presently have a celestron 7ah powertank, it tends to last for about 90mins when fully charged powering my HEQ5pro. I was looking for an alternative. I have considered the jump starter units (EG Halfords phase 4) but I've read on here that they are not ideal as they are designed for sudden outputs of power and that the batteries wear quickly) Please feel free to correct me on this.

I am considering building a simple power bank as follows and wanted to see if you folks thought it would work.

12v 17ah Lead Acid rechargeable battery, 12v cigarette lighter socket, inline fuse, on/off toggle switch, voltmeter, small plastic toolbox to house it and a trickle charger.

I've priced it up and looks like I can get all the components for around £40.

I'd welcome your thoughts and suggestions or alternative ideas. Budget £50

Thanks

Simon

 

[Steve Clay]

Hi,

Why dont you just replace the battery in the tank you have.

Steve

[Simon Dunsmore]

Hi Steve, 

Is that an easy thing to do? I thought I read somewhere that it wasn't possible. I've always kept the battery charged in that tank so I'm not sure why it only lasts for 90mins.

Thanks 

Simon 

[Steve Clay]

Hi Simon,

Yep, just open it up. You could put a better battery in for less than half your budget. Look at disability scooter batteries as they are designed for steady drain as opossed to say a motorcycle battery. Or RC hobby 12v batteries like this:

https://howesmodels.co.uk/product/power-sonic-ps-1270-12-volt-7ah-rechargeable-lead-acid-battery-copy/

Depending on how much room there is in the tank you could fashion a way of getting 2 in whereby you could switch between the 2 or have 14ah. 

Steve

Edited April 7, 2020 by Steve Clay
Link

[PEMS]

Any standard type lead acid battery has the problem that they are intended for what could be described as a short intense discharge - starting a car engine. For astronomy use you want one that is intended for a long slow discharge.

Standard lead acid batteres will discharge to around half capacity then the internal plate damage by possible deformation or caking on the surface. After which they damage more and quicker.

Batteries for mobiliuty scooters and golf trolly's are better but both cost more.

One I did read of was a Lithium Motor Cycle battery. Small and I think the capacity was 4Ah so somewhat smaller, cost was reasonable however. May be an option to search for slightly larger ones but I would expect the cost to rise rapidly.

A normal lead acid would be OK if you could go out and after a set time pack up even if the sky was good everything running fine. In effect a good night and you pack up early, Unfortunately that doesn't happen.

Having reread the initial post are you only observing or imaging also? 90 minutes seems short and even the mentioned motor cycle Lithium I would have expected the same or longer as a reasonable amount of time the HEQ5 should be just tracking.

I have noticed the term "Deep Cycle" used on many however it seems a little suspect as some read a AGM and that may not be 100% a deep cycle.

[Simon Dunsmore]

14 minutes ago, Steve Clay said:

Hi Simon,

Yep, just open it up. You could put a better battery in for less than half your budget. Look at disability scooter batteries as they are designed for steady drain as opossed to say a motorcycle battery. Or RC hobby 12v batteries like this:

https://howesmodels.co.uk/product/power-sonic-ps-1270-12-volt-7ah-rechargeable-lead-acid-battery-copy/

Depending on how much room there is in the tank you could fashion a way of getting 2 in whereby you could switch between the 2 or have 14ah. 

Steve

Thanks Steve, 

Great bit of advice. I just ordered a lead acid battery 9ah with same dimensions and terminals + an intelligent trickle charger to ensure it doesn't overcharge or run down. 

Thanks again for your help 

Simon 

[Bamo]

Hi Simon, I recently managed to have my own sustainable power supply cause I had the same problem with the 7Ah power tanks. They were a bit expensive and didn't provide sufficient power for the whole night. I'll tell you what I have bought. The setup is not so handsom "yet" but I tried it and it works perfectly.

1. 60 Ah semi-traction 12V battery. Can be in a range of €80. Your can set your own preference.

(Varta 60Ah accu Professional MF LFD60, 930060056, 12V)

2. Battery charger, cheap DUNLOP, slow charging but does a great job so far. between €15 and €20.

https://www.groupon.co.uk/deals/gg-groupon-goods-global-gmb-h-2340-158

3. Inverter DC/AC 500W. This is an amazing solution, will cost in a range of €50.

https://www.amazon.nl/dp/B07D4B1JXB/ref=pe_19967891_406998361_TE_SCE_dp_1

Bamo

[Simon Dunsmore]

Hi Bamo, 

Thanks for your message. Yes, you're right the powertanks are expensive but the replacement 9amp hr seems to be working better. 

Post some photos when you get a chance. 

Take care, stay safe, and clear skies 

Simon