Briefcase powerbank for camping etc

[KirstinS]

afternoon all

I have tons of 18650 cells at the moment and have several camping trips lined up. I also have a aluminium briefcase that used to contain a set of kitchen knives etc.

My thought is to create a big mobile power pack using the 18650s with an integrated 12v car style cigarette socket and a 150w 12v to 240v dc/ac invertor to run low powered mains items such as laptop charger

My main question that I struggling to get any certainly on is this

Cigarette sockets and these inverters expect 12v but, using lithium batteries they will get 11.1v nominal. Will this difference be ok ? Presumably in cars there is some sort of voltage stabilizer between the car battery and the socket ?

My design/idea is actually a lot more developed than this (including fuses, battery monitoring etc)…….but all on the basis that 11.1v nominal will not cause any issues !

Any thoughts on this point ?

many thanks
Kirstin

 

[neptune]

As far as I know there is no voltage stabiliser between a car battery and the fag lighter socket. The voltage will vary according to if the engine is running, and if so, at what RPM. The regulator in the alternator will usually limit the voltage to 13.4 max. Try it on 11.1 volts. If there are problems, add another cell in each series string, and look into adding a simple voltage regulator. These are cheap and east to install, involving only three terminals, Negative, positive in, and positive out. Choose one that can handle the max current you will draw.

 

[KirstinS]

To be honest I'd rather not just wing this one and hope it works

Prefer to step to 14.8v and have a voltage regulator.

I'm thinking of 10a max setup

I've had a little look round net. Would a 24v to 12v regulator be my best bet ? Like this

http://bit.ly/NnUMLP

Many thanks

 

[KirstinS]

Looks like the 12 to 240v investors cannot take less than 11v which means I can really make use of the full Ah available to me unless I get a voltage regulator

If I can find one that works with 10v minimum then I won't need it

I think .....,,

 

[neptune]

You can buy cheap 12 volt regulators for about a couple of quid. However they are usually rated at about one to one and a half amps output, not enough to run any but the smallest inverters, not adequate for your job. Probably best to find an inverter that will run on 10 volts if you can. Every time voltage is converted from one value to another there are losses. The best theoretical answer would be to make up your cells into packs that would run a laptop, and change them as necessary. I have never owned a laptop, but I suspect that this would not be practical. When camping, I get around the problem of charging my e cigs, simply by owning about six batteries.

 

[Deleted member 4366]

Most inverters have a low-voltage cut-off to protect the battery. Your 18650s will sag a lot a 10 amps, so the LVC will activate. You'd be better with 4 cell groups for 14.4v.

Some inverters need to maintain a certain amount of current on the output otherwise they assume that they're idle, and shut down. This can happen with a phone charger that only draws a tiny current. Some inverters have a USB output, which is therefore better for charging a mobile phone.

Aldi sold such a power pack, but with a SLA in it. You could probably find a used one on Ebay and swap the battery. Here's a different one:
http://www.ebay.co.uk/itm/Halfords-Power-Pack-200-with-Compressor-Inverter-RRP-99-/261420714118?pt=LH_DefaultDomain_3&hash=item3cdde38886

 

[KirstinS]

I think I have found a few invertors that shut down at 10v so no regulator required

To d8veh point I intend to use in two ways

1) the battery feeds a 12v cigar socket to which I will plug in a usb adaptor that will charge usb devices

2) the invertor which will run bigger mains items eg laptop charger at about 85w for my MacBook, or perhaps a small fridge unit , maybe even a small LCD tv


I think this means the LVC should not ever cut out as small items will come off the DC supply not the invertor


It also negates the issue of unnecessary wastage as I will not be converting Dc to ac unless actually required by the end device

That's the plan anyway

 

[jackhandy]

[quote="d8veh, post: 210970,

Aldi sold such a power pack, but with a SLA in it/quote]

I have one of the Aldi power packs, branded Auto xs, with a 17.2ah sla in it.

2 years old & started my 2.5 litre diesel from flat, no problem.

Lovely bit of kit.

 

[KirstinS]

i find the 18650 booster pack dont sag too badly even on my bike which has a 17a controller but maybe thats becuase I use 6 x 2200mah cells for each 3.7vv block i.e my 11.1v booster pack is made of 18 cells and is around 13ah

I've made two of these 13ah 11.1v boosters and have wired them with xt60 that they can be easily put in parrellel for use in the powersuitcase

I know you CAN buy stuff like this but I wanted to make something cool and really useful for practically nothing out of parts otherwise headed for recycling. Cells are all free, aluminium briefcase has been in the shed for years and, with the exception of the invertor, total costs of parts will be under a tenner

its all for the joy and furtherance of the great tradion of English garden shed inventions and tomfoolery

And I'm going to give it a big red missile launch button too