Working out battery capacity

[cuivenion]

Hi, My maths is dreadful and I'm hoping to get some help. I'm thinking about getting this to power my rig:

https://www.amazon.co.uk/Portable-Generator-GIARIDE-Inverter-Emergency/dp/B081CGK6VK/ref=sxbs_sxwds-stvp?crid=3M9MDYRHN3W2J&keywords=portable+power+station&pd_rd_i=B081CGK6VK&pd_rd_r=4e037fdd-bb2a-455e-8667-1d3ed5b87dbe&pd_rd_w=zgSxo&pd_rd_wg=aFtjQ&pf_rd_p=7dc56c0d-8a5f-4d97-9143-7233b106859a&pf_rd_r=GSGPDFGQGG92X0FREGK6&qid=1577548918&refinements=p_89%3AALLPOWERS&rnid=1632651031&sprefix=portable+power%2Caps%2C185

It says it has 40800mah at 3.7v, what would this be at 12v? This would be giving me a ballpark figure. I'm running:

Heq5 Mount 12v

Laptop (12v to 20v converter)

EOS 600d ( 5v to 7.4v power supply)

Dew band (12v 600ma max)

Any advice would be great thanks.

[Davey-T]

Confusing description, should run most of your gear I guess but doubt if it will do a laptop, I use a separate 24ah Tracer LiFPO just to power my laptop all night.

Dave

[DaveL59]

so its states a capacity of 40Ah at 3.7v, for 12v that'd be approx 25-32% of the stated capacity so around 10-12Ah effectively.

Hope that helps. Are you planning to run all this from that one power pack and what runtime would you be hoping for?

You'll see some losses ramping to 20v but maybe less that using the mains out into a laptop PSU so might be worth testing both ways and see which is better in terms of battery drain. 

 

[cuivenion]

Thanks for the replies. I'd have to use the the 12v dc output and power the laptop and mount from it together because I don't think the ac and dc outputs can be powered at the same time. I'm presuming using 220v ac output for the mount and laptop would be very inefficient.

Edited December 28, 2019 by cuivenion

[cuivenion]

If I could run all the devices and get about 6 hours I'd be happy.

[Gina]

Says AC O/P is 110v so won't run UK mains devices.

[cuivenion]

Ah, just spotted that, maybe this one then.

https://www.amazon.co.uk/FLOUREON-Portable-Generator-220V-240V-Emergency/dp/B0822FB7T8/ref=sr_1_160?keywords=portable%2Bgenerator&qid=1577547718&sr=8-160&th=1

[jambouk]

The one you've just linked to says it can run a CPAP machine, so even if you fall asleep and start snoring you'll be OK

These kind of power tanks are OK if running a mount for a few hours, but if you want to reliably power a laptop, dew bands, DSLR and mount etc for 6 hours, then it won't be sufficient. Even if it is sufficient for a shorter period, you'll be deeply discharging the battery each time, and over time it won't thank you for that..

Convert all your devices current requirements into Watts. Then add these together and multiply for the number of hours you want to run for; if you are planning to go camping in a remote site and use the kit for more than one night on the same battery, don't forget to add in the hours on the subsequent nights too.

Once you have a total value of Watts, decide if you want to use a conventional lead acid battery (in which case I would make sure your watts are not more than 20% of the capacity of the battery), or if using a deep cycle battery then I would look at getting one with capacity twice your Watts, so it doesn't get more than 50% discharged.

I suspect you really need something with capacity of >100 amp hours if you really want to run all this stuff for 6 hours. In reality I get too cold and am either already too tired or end up too tired, and have work or life commitments to last more than 2 hours, unless imaging at home when I can run off the mains and get a little buzz off the mount when I touch it, which is always exciting. Never combine mains electricity and damp conditions.

James

 

[Gina]

If you feel a tickle off your mount it isn't earthed properly and should be attended to!!  URGENTLY!!  A hazard to both yourself and your equipment!  For my observatory I have a 4ft copper ground rod and run 10mm² earth bonding cable from that to my mount and from there to the power distribution box in my warm room.  Incoming mains power goes through an RCD and fuses to supply power and lighting.

[DaveL59]

I'd agree with James on capacity suggestions, for extended running you need to be looking at much more than the smaller packs can deliver.

For lead batteries they will be heavy and you should avoid car batteries - they are meant to deliver high cranking current in short bursts but not for long slow discharge so will fail quicker. Regular SLA also don't like being run flat, below 50% and you're shortening the life of the battery. Leisure are better for this as they're designed for deep discharge, but again heavy and its best to avoid cycling them too hard. You need to store lead batteries charged and maintained too.

Lighter weight Lithium cells are around, LiFePo is a good example and you could pitch for 50% AH rating vs the lead battery and get the same runtime, i.e., 10AH is a reasonable swap for a 17AH lead battery. That's because volts will drop off as battery discharges on a lead cell, where Li types will hold up longer but have a sharp drop off as they near discharged levels, the in-built battery management should protect the cells from abuse. Unfortunately these are still quite expensive but potentially will outlast lead batteries 3x which may balance that out. They also don't need to be charge maintained in the way lead batteries do.

 

Oh and don't forget when totting up the load to also allow for conversion losses, you may need to add 15% or so to the load total. Then also allow for AH capacity "loss" if operating in cold environments, batteries don't like the cold, some more than others.

Edited December 29, 2019 by DaveL59