Portable Power

MI0PYN

MI0PYN

Super Member
I've been playing around with a few options around portable power for QRP rigs. I built a few powerpacks based on 3000mAH 18650 cells, but I think the BMS boards I got from China may have been suspect, I built 2 3S2P packs and found that they worked OK, but the hardware I used to assemble them wasn't great. They also had a lot of capacity that I was never fully utilising with the QRP rigs I was using.

As a result, I decided to try something else, and I thought I'd document how I was getting on here in case anyone else was interested.

My plan was two-fold:
[list type=decimal]
[*]Create a battery tray to hold 3 18650 cells for a 3S1P pack, with an integrated BMS board so the pack could either be charged as is, or have individual cells swapped out for charging.
[*]Once that was working satisfactorily, use that as a base for a clip on accessory for the TX-500 QRP transmitter which I'm currently lusting after.
[/list]

The idea was to have a 3000mAH 3S Li-Ion pack that could be used for a SOTA activation or other portable activation, and which could be charged using any standard Li-Ion charger. However, for longer trips, a spare set of 18650 cells could be carried and charged independently from a USB powerbank or similar, with the two sets of cells swapped when they became depleted. This would allow a single battery pack to be used for short activations, but allow spare cells (and charger) to be carried for very little weight penalty. I was thinking primarily of camping trips in my own case.

As this thread develops, I'll show my ideas, and hopefully how they come into being. I'll be using TinkerCAD and a friend's 3D printer for prototyping and if it all works, I'll make the STL files available for anyone who may want them. If it all works...  pq
 
Here is the first draft of the tray itself.

There are a few refinements to do, such as putting little detents in the sides that will allow a lid to be clipped on and such, but this is what I'm going to get printed as a first try.
 

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I've made some progress on this project, a mate printed me a prototype of the battery holder. It's a draft print so a little rough, but definitely good enough to build a prototype of the whole thing.

I got a few small BMS boards as well, so hopefully the next post after this one will have a rough but functional model.

Here's a pic of the printed case.
 

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I took an early lunch break... :cool::cool::cool:

Here is the first working prototype:
 

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Well, for a draft pint I would say it looks quite believable! ;)

I see you have managed to get hold of some ex-laptop batteries? (I guessing based on the white resin and adhesive, some of mine look the same).

Does the battery management system (BMS) board charge/control the cells in series as a pack, or does it control/charge them individually similar to how the laptop battery controllers work?

73, Mark...
 
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The BMS is connected to each cell individually. In LiPo battery parlance there are balancing leads, not sure if the same terminology applies to LiIon too.

Essentially, the BMS has Bat -ve, 3.7v, 7.4v and 11.1v on the battery end and the standard positive and negative at the charge/load end.

I did get one old laptop battery with only 1 duff cell, so I can experiment away with a set of cells at my leisure. Still looking for more but they're difficult to get, unless you're prepared to pay ?5 a piece for new ones.
 
MI0PYN said:
I did get one old laptop battery with only 1 duff cell, so I can experiment away with a set of cells at my leisure. Still looking for more but they're difficult to get, unless you're prepared to pay ?5 a piece for new ones.
Click to expand...

Go to eBay and use the search phrase "used laptop battery job lot" (y)

You'll be amazed!

73, Mark...
 
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Maybe a bit of overkill, but I came across this video on YouTube covering the use of recovered (i.e. 'scrap') laptop batteries.

I thought maybe some of the tools and or techniques used might be useful (albeit scaled down!) for the project under discussion here.

https://www.youtube.com/watch?v=PenPYwa00CA

73, Mark...
 
Hi all
New member here.
Very interesting info on here.
Anyone using these power packs in real life yet?
I have built a QCX in 40m flavour and looking for portable power options when lockdown finishes.

73
Craig
 
G4MNX said:
Hi all
New member here.
Very interesting info on here.
Anyone using these power packs in real life yet?
I have built a QCX in 40m flavour and looking for portable power options when lockdown finishes.

73
Craig
Click to expand...
Hiya Craig (welcome to the forum!)

Not sure if Stefan (MI0PYN) is still using his pack design, I think I spotted one for sale with one of his rigs on another site so maybe he has gone in to mass production! 😋

I've tinkered around just using ex laptop batteries and either a 2-cell holder, or a 3-cell holder for them, both worked fine for QRP use. I had to remove the cells for charging, but it only takes a few seconds. Stefan's system allows charging to take place with the cells in the holder which is very convenient.

Depending on what voltage you require you could maybe use one of the USB power-banks, and with the aid of a boost converter you could up the 5V output to say 9V or 12V. Some of the power-banks are rated at 20,000mAh so plenty of 'juice' for a session on a hilltop or park.

Boost converters sell for a couple of pounds each, not much anyhow, and you might have a suitable power-bank laying around your QTH already (we've got about four or five here of various capacities).

The only issue that might occur with such a system is RF noise from the boost unit itself, you would have to experiment I guess and see what worked. Obviously, if you went down the ex laptop battery route you power would be noise free hopefully. ;D

Just for reference I also have a few sealed lead-acid batteries (can't think of the proper name off the top of my head), which work OK, but they are a lot heavier than the laptop cells when you consider the energy you can get out of them, and they are very critical about charging currents/times whereas the laptop cells seem almost indestructible! 😀

Few things to think about there for now...

73, Mark.
 
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I made 2 of them as I had 2 of the BMS boards, not quite mass production yet  :D

I've found it works well on the KX2 (which is why one was included when the KX2 was offered for sale as Mark noticed) and the ability to take a second set of fully charged cells to swap out in the field is a real advantage if you were out for longer, or even a multiday trip.

The sealed Lead-Acid batteries (you may have meant AGM - Absorbed Glass Mat Mark) actually have a lower energy density than LiIon batteries, and I've found them impractical for /P use.

For a situation where weight is less of an issue, such as in a go-box, I've built a LiFePo battery out of 32700 cells (I think) which has 20Ah capacity for about the same weight as a 10Ah electric wheelchair 12V sealed lead acid battery. It's a drop in replacement for most SLABs if you have the right BMS board on it.
 
G4MNX said:
I have built a QCX in 40m flavour and looking for portable power options when lockdown finishes.
Click to expand...

I'm not sure how handy you are with a soldering iron and general fettling, but I suspect you'd be ok having built a QCX.
If you have access to a 3d printer, I can send you the STL for the tray and you can print one to mess about with.
If you don't have access, I'll print you one and send it out to you if you PM me your address.
Construction is easy enough, the trickiest thing is making the contact tabs for each end of the cell and soldering the leads on to them. I had to pack them out with some packing foam to give them the required spring to make good contact with the ends of the cells. 1mm OD wire was used for connecting the cells to the BMS and the BMS to the Anderson PowerPoles and just fits snugly in the channels designed for holding the wire.

Stefan MI0PYN
 
Hi Stefan,
Many thanks for your assistance on this. PM reply sent.
Your printed battery packs sound ideal and with the ability to swap out cells with charged ones.

73
Craig
 
A big shout out to Stefan,
3d printed box, nickel contact strips and bums board received today.
Thank you so much :*:
Just got to work out the wiring and then assemble.
Thanks again Stefan.

Craig
 
No problem at all Craig.

Mark G0KZZ has helped me out a lot too, so I want to pay it forward where I can.

73,
Stefan MI0PYN
 
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