Author Topic: Sheddi's power bank build thread  (Read 351 times)

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Offline sheddi

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Sheddi's power bank build thread
« on: June 27, 2021, 12:01:23 PM »
I split this topic out from RonnyRonins one so that I wasn't messing up his build thread too much when I wander off-topic (as I'm prone to doing).

My goal is different to RR's; I want a small portable system I can use in and around a vehicle while car camping or whatever. My current daily driver is a 2004 Fiat Panda which has many things going for it (low price and great gas mileage) but isn't really set up for off-grid life. I could simply use and abuse the starter battery (as described on Frater Secessus excellent RV Wiki) but I'm fortunate enough to be doing this deliberately, and to have disposable income. so I thought I'd look for a better option.

This project by Benjamin Nelson is my general inspiration:

Instructable: https://www.instructables.com/Ammo-Can-Solar-Power-Supply/



And I'm aiming to achieve a similar capability to a Jackery 240 but at half the price (and hopefully have more fun building it).

I have managed to scrounge up a .50-cal ammo box, so that's what I'll be building my DIY system in.

I have a 12V SLA battery kicking around but it's pretty much dead; I can use it as a design aid but it's not going to be any use in a working power system. I was intending to use a LiFePO4 battery from AliExpress but, having ordered it in early April, it didn't arrive. I eventually got refunded by AliExpress (not by the seller, the seller claimed it had been delivered despite the tracking saying nothing of the kind) - but I digress. I need another battery.
« Last Edit: August 23, 2021, 04:11:37 PM by sheddi »

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #1 on: July 06, 2021, 07:41:19 AM »
I was intending to use a LiFePO4 battery from AliExpress but, having ordered it in early April, it didn't arrive.

Guess what turned up today, in a battered foam box? Yes, the missing battery!



It's on charge right now. When it's full I'll do a discharge test. The chance of it actually being 38Ah is nil but it *might* be 20Ah.

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #2 on: July 11, 2021, 01:37:16 PM »
Had time to do a discharge test on that battery today. I needed to find my XT60 connectors then make up a cable, as I didn't think the croc clip test leads I use for smaller stuff would be happy passing five amps or so.

I used my thermoelectric cool box as a load; it draws around 5.5 amps pretty consistently.

The battery was quite happy to drive the coolbox. The voltage was pretty consistent throughout the discharge, as you might expect for LiFePO4 chemistry. When the voltage fell below ~10.8v the BMS cut it off completely, as it should.

And the capacity? Well, the battery lasted between 3 and 3.5 hours (dinner prevented me getting a more accurate number) which means the capacity of the battery is somewhere in the range 17-19 amp-hours. So roughly half the claimed capacity, but close to what I was expecting it to be. For the US$50 it cost (or would have, if it hadn't been lost in the post), I'm happy. (Seriously, that's less than $3 per Ah. Buying a similar battery locally to me would be  over twice that.)

What I need to do now is get on with building it into a power system!
« Last Edit: September 04, 2021, 11:13:07 AM by sheddi »

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #3 on: July 17, 2021, 11:52:08 AM »
Today I embarked on a bit of CAD (cardboard-aided design).

Parts list (links, where provided, are to ebay.com unless stated otherwise):

50-cal ammo box
20Ah LiFePO4 battery (link is AliExpress)
10A solar controller
Accessory panel
XT60H connectors ("H" connectors include a clip-on contact cover, otherwise you will need heatshrink or electrical tape)
16 AWG cable, soldering iron, solder
Cardboard, craft knife
Tea (optional :) )


The 20Ah 4S3P 32700-cell LiFePO4 battery fits quite nicely across a 50-cal ammo box:


I decided to use the XT60 connector on the battery for my power bank. It seems a much more reliable connector than the 5.5/2.1mm power plug option. I guess I could've swapped it for something else but I couldn't think of another option that was worth the effort.

To connect the battery to my 10A solar controller, I made a short XT60 pigtail like this:


Now to the cardboard! I cut a piece the same width as the ammo box and fitted to it my accessory panel. Various options were on offer through the usual on-line marketplaces but I chose this one with a switch, a 12V cigar socket and a twin QC3.0 USB socket (which includes a LED voltmeter, a nice touch but probably unnecessary in this application).

This particular panel came complete with pre-made wiring for the back end, including a 20mm 10A fuse & holder:


Putting it all together and switching on, it looks fairly tidy and appears to work:


I ned to get some 4mm ply or similar to replace the cardboard. I also need to make a charging pigtail for the input to the solar controller. That might end up being another XT60 (MC4 connectors seem excessive for something this small).

Does anyone have any thoughts/suggestions?


Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #4 on: July 18, 2021, 04:58:11 AM »
A short digression. I have a few sealed lead-acid batteries hanging around the house in varying degrees of decrepitude. I thought I'd do a quick comparison with the LiFePO4 (LFP) pack for general informational purposes.

Here's a photo of the three batteries I'm comparing:

  • Yuasa NP7-12, 12V 7Ah SLA, 150x56x100 mm lxwxh (6"x2.2"x4"), 2.65kg (5.8 lbs).
  • Chinese 4S3P 32700, 12v 20Ah LFP, 140x72x106 mm (5.6"x2.9"x4.2"), 1.75kg (3.9 lbs).
  • Yuasa Reliart RE12-12, 12V 12Ah SLA, 150x100x100 mm (6"x4"x4"), 4.05kg (8.9 lbs).
What should be obvious from the photo is that the LFP pack is smaller than the 12Ah SLA despite having 60% more nominal capacity. Not so obvious from the photo, but evident when you handle them, it also weighs less than the 7Ah SLA.

And of course you get to use the full 20Ah capacity of the LFP battery, whereas the 50% depth-of-discharge rule of thumb means you would only get 6Ah from the larger SLA. Put another way, three of the larger SLA batteries would give a similar day-to-day capacity to the LFP but would then weigh 12kg / 27lbs.

Another comparison for you: lhe lead-acid starter battery in my Fiat Panda is generally like this, has a nominal capacity of 40Ah and weighs 11kg (24lbs). By the 50% rule it has the same usable capacity as the LFP one.

Quick edit to add:
I'm using the prototype power bank as built, in cardboard, today so I can run a 12v fan (this sort of thing). It's unusally warm here today - nothing like the PNW has seen but still in the high 80s, which is hot for England!

(The closest reliable weather stations are RAF Benson or London Heathrow).

« Last Edit: July 23, 2021, 03:32:56 AM by sheddi »

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #5 on: August 23, 2021, 12:49:06 PM »
I've made a couple of steps more progress with this project. It now looks like this:



Mostly, I've replaced the cardboard with a piece of 4mm ply. I didn't have 28mm hole saw for the lighter / USB/ switch panel cut-outs so I drilled the closest I had (22mm) and then opened the holes up using a sanding drum in my Dremel*. The same Dremel (and the same sanding drum) was used for most of the sanding and shaping.

There's another piece of 4mm ply under the battery, and the to-do list includes a couple of vertical pieces so there's a box-within-a-box that will let me pull the gubbins out of it if I want to add/change/upgrade any parts.

I still need to make up a solar charging pigtail but the one pictured works OK with mini alligator clips for now.

I also need to get some black screws for the solar controller ...

Like most of my projects, this will take a while to finish!

* It's not really a Dremel but "rotary tool" is too vague a name, IMHO.
« Last Edit: August 23, 2021, 04:14:11 PM by sheddi »

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #6 on: September 02, 2021, 01:55:50 PM »
You might remember my failed efforts to buy a cheap solar panel in the Before Times. Edited lowlights follow.

Quote from: Sheddi Wed Mar 24, 2021 6:10 pm
In a bout of unbridled optimism I bought one of those suspicious-looking solar panels from eBay. This one only claimed 20 watts and it also quoted 1.1 amps at 18 volts, so it didn't seem too outrageous a claim. Buying it from ebay.co.uk and using a discount code I got it for £14 which is about US$20 - a dollar a watt, which didn't seem too bad a deal.

It arrived today and (as well as the cells being skewed in the panel) there was quite obviously something wrong with it.



So It's being returned :rofl:

Other than the wonky encapsulation and the broken cell, however, it looked kinda ok so I've ordered a replacement.
and
Quote from: Sheddi Mon Mar 29, 2021 5:32 pm
I returned the original and ordered another, from a different seller. When the eBay invoice came through it was from the same business in China - it seems both sellers were fronting for the same supplier!

The second panel arrived on Saturday but we didn't get any sun worthy of the name until today. This panel looked better - no obvious flaws - but once I got onto electrical tests there was clearly something wrong with it (if anyone can suggest exactly what, based on the following, I'd appreciate being educated).

Voc = around 17 volts. It was initially 17.6 volts but dropped off quickly to 16.9-ish as the panel warmed up. It definitely wasn't the 21-22 volts I'd expect from a 36-cell panel under a clear sky just before local solar noon.

Isc = 0.61 amps. Rather disappointing for a 20-watt panel but what you'd expect from a 10-watt one (and the dimensions of the panel are consistent with 10 watts nominal output, at typical cell efficiencies).

I then hooked it up to the same 6Ah AGM motorbike battery and cheap Chinese shunt regulator I used in this topic. I added a (nominally) 5 watt LED lamp to the battery as a load to make sure I wasn't at 100% SOC. Disappointingly the panel would only deliver 0.05A into the regulator at an indicated 12.5v on the reg.

I tried without the regulator, connecting the panel direct to the battery. Still only 0.05A with Vbat of 12.5v.

Finally I connected the panel direct to the lamp. It illuminated the lamp giving approx. 9v and 0.2A.

Maybe that panel had a high internal resistance, somewhere? Either way, it's not working properly. So that one's getting returned too and, after 2 failures from 2 purchases, I'm giving up on those particular solar panels!

Why am I reminding you of this inglorious failure? Because I've recently purchased an entirely different panel and this one seems to work. Details in the next post.

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #7 on: September 02, 2021, 02:15:44 PM »
Argos, a major UK high street retailer, has an eBay.co.uk presence. A lot of the stuff they sell there is their regular stock but they also use eBay to shift end-of-line and clearance items. I was idly browsing the "solar panels" section of eBay and saw that Argos were selling Polaroid SP50 folding 50W solar panels for £45 including 48h delivery (roughly US$62). That's somewhat more than I was originally hoping to pay but, as they say in the shampoo commercials, "you're worth it".



(Note the panel comes with charging pigtails but the power bank pictured in the video is an entirely separate product.)

The panel arrived today, new in box. I took it out into the back garden and, even though it was late in the day, managed to catch a bit of reasonable sunshine. Voc was 22v and Isc was 2.3A, which isn't too far form the rated full-sun values of 22.3V and 3.04A. If we get some sunshine nearer to noon over the weekend I'll do some more tests and take some photos.

As a companion to my DIY power bank, this looks to be perfect :)

Offline Crosscut

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Re: Sheddi's power bank build thread
« Reply #8 on: September 03, 2021, 04:53:37 AM »
Somehow I missed your update on the 23rd sheddi, it's looking good!  My projects are always kludgey in comparison :)

Just a thought if you have enough spare room in the ammo can, a 12v adjustable power adapter.

And (or) a USB step up/down power supply.  Just picked one of those up a few weeks ago, haven't tested it yet but it'll be added to the BOV kit with the 12v one above eventually.  Could come in handy for powering/charging most small electronic devices that require odd voltages or if someone lost their DC charging adapter, and more efficient than using an inverter if all they had was the AC power adapter for the device.

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #9 on: September 03, 2021, 08:16:45 AM »
Thanks Crosscut, the photos are just from my cellphone but they seem to come out pretty well.

I've got one of those adjustable power adapters around here somewhere, I'll dig it out and slip it into the box. And I haven't seen that sort of USB power supply before. It looks very useful, I'll take a look and see if I can find one over here.

Right at the moment it's dull and overcast, not great weather for trying out solar panels. hopefully it will brighten up over the weekend.

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #10 on: September 03, 2021, 10:36:38 AM »
We got some sunshine! Not completely clear skies but enough to try stuff out.

Here's the general setup. I clipped the solar panel to a length of timber, then used a couple of alligator clip test leads to connect the Powerpole output into my power bank (via my muntimeter so I could measure current). The thermoelectric coolbox is plugged into the power bank as a load to keep the battery slightly discharged. Apologies for the general state of my back garden, the grass badly needs mowing.



The photo above was pretty much as bright as it got. In dull conditions, where I wasn't casting a shadow, I was getting 0.6 amps or thereabouts, roughly 8 watts (no load in this photo):



The best reading I managed to photograph was 2.3 amps, around 30 watts (you can see where I've plugged in the cooler):



If you compare the second and third photos you can see how much brighter it was in the latter one.

Yes, I count this as a successful test. My objective was a power bank for car camping. The Polaroid solar panel is physically as large as I'd want to take camping, and should give me something like 120Wh a day in sheddi's-gone-camping weather. Together with the 240Wh in the battery that's almost 500Wh for a weekend camp; I'm unlikely to need any more than that.
« Last Edit: September 03, 2021, 10:49:59 AM by sheddi »

Offline RonnyRonin

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Re: Sheddi's power bank build thread
« Reply #11 on: September 03, 2021, 09:45:41 PM »
Very cool! You've certainly blown past my progress; I've completely stalled out at batteries.

locally a 1000Wh ballpark battery is around $700, but if I'm doing my math right I could get about the same capacity for around $200 with multiples of the battery you are using? Could you confirm my math on that?
share your tobacco and your kindling, but never your sauna or your woman.

Offline lurkedthere

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Re: Sheddi's power bank build thread
« Reply #12 on: September 03, 2021, 10:39:53 PM »
I keep one of these in the car. You never know who might need a charge.

CNL 10 IN 1 UNIVERSAL MULTIPLE LEAD USB DATA SYNC CHARGER CABLE FOR MOBILE PHONE / MP3 DEVICES https://www.amazon.co.uk/dp/B008CNWSOI/ref=cm_sw_r_u_apap_CxeCUXQoyW3S4

No longer available at this particular vendor, but there are others. I wouldn't leave it unattended.
« Last Edit: September 03, 2021, 10:48:37 PM by lurkedthere »

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #13 on: September 04, 2021, 03:55:29 AM »
Very cool! You've certainly blown past my progress; I've completely stalled out at batteries.

locally a 1000Wh ballpark battery is around $700, but if I'm doing my math right I could get about the same capacity for around $200 with multiples of the battery you are using? Could you confirm my math on that?

Thanks, your thread inspired me in the first place so I wouldn't have done any of this if you hadn't started!

Yes, my battery is 20Ah at a nominal 12V so 240Wh, four of them would be 960Wh. If you can find a reliable supplier (or want to take pot luck with AliExpress) four of them would work for you. However, in your position I'd consider something like this, a 12v 100Ah battery for US$220-ish:

https://www.aliexpress.com/item/1005003229801167.html

That is just an example but the seller has been trading since 2017 and has relatively good feedback (95%+ positive, good for AliExpress). Have a poke around and do your due diligence on any seller or product on AliExpress.

Edit to add: Do remember that LiFePO4 batteries don't like being charges below freezing. This isn't likely to be a problem for me, considering my AO and intended use, and hopefully won't be an issue in your apartment either!
« Last Edit: September 04, 2021, 10:43:54 AM by sheddi »

Offline RonnyRonin

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Re: Sheddi's power bank build thread
« Reply #14 on: September 04, 2021, 10:36:02 AM »
Thanks for the sanity check.

I'm a bit nervous because

1) I've never bought anything from aliexpress
2) similar batteries are double or more money everywhere else
3) there are so so many options on aliexpress

Time to binge youtube reviews I guess...

On your battery box you surely have room for a second cell; could you squeeze a third one in or would it be too tight?
share your tobacco and your kindling, but never your sauna or your woman.

Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #15 on: September 04, 2021, 11:09:29 AM »
Thanks for the sanity check.

I'm a bit nervous because

1) I've never bought anything from aliexpress
2) similar batteries are double or more money everywhere else
3) there are so so many options on aliexpress

Time to binge youtube reviews I guess...

On your battery box you surely have room for a second cell; could you squeeze a third one in or would it be too tight?

I was nervous too! I only started buying there 18 months ago, when I couldn't find a FFP2/N95 mask anywhere in the UK. I've placed a couple-dozen thirty-eight :o orders since then, most of them only for < $10 and the majority have turned up and worked. Where things have gone wrong - either not delivered, or (in the case of those li-ion batteries) not as described - AliExpress's complaints process has worked out for me.

The two highest-value items have been the 25Ah cells for my home battery and the additional 60Ah ones I've ordered to make that same battery larger. Both orders were around $350 and made me slightly worried. The 25Ah ones arrived safely, which was a great relief. I'm expecting the 60Ah ones towards the end of this month.

My three four rules (which might or might not work for you) are:
  • Choose a seller who has been in business for a while (preferably years, not weeks)
  • Choose a seller with a significant number of reviews, distributed in space (nationality) and time
  • Choose a product with good reviews and buyers reporting that they have actually received it, with photos
  • Pay with PayPal so you've got PayPal's complaints procedure to fall back on if everythign else fails
I definitely have room for a second battery in my case. A third might fit but I'm using the space where it would go for the behind-panel parts of the pack; the cables, the fuseholders, the hidden parts of the sockets and switches. Here's a photo to show what I mean. The white foam is just to locate the battery centrally in the box, and stop the screws in the panel from damaging it.



In principle I could turn the battery through 90 degrees which might let me squeeze three in the ammo box, but I'd lose most of the space under the lid of the box.



Does this help?
« Last Edit: September 04, 2021, 11:34:29 AM by sheddi »

Offline RonnyRonin

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Re: Sheddi's power bank build thread
« Reply #16 on: September 04, 2021, 11:59:04 AM »
That helps a lot!

720Wh in an ammo can is incredible; I guess at that point all you'd be losing over a commercial model is more plugs/socks and an inverter, all of which could be run externally of course. Maybe cooling would start to be an issue packed that tightly? looks like plenty of room opposite the plug bank for a fan if needed

You've got me rethinking my own box now; I had assumed I'd end up with a battery closer to a car battery size than your cells; I might be able to go with a larger ammo can (like a 20mm or a 40mm can) or the smaller ridgid tool box rather than the medium one I have earmarked.
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Offline sheddi

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Re: Sheddi's power bank build thread
« Reply #17 on: September 04, 2021, 12:21:58 PM »
Just to add:

If you don't want to order from China and wait 6-12 weeks for the battry to turn up, amazon.com offers a selection of 100Ah LiFePO4 batteries for $400-$450 or so. This might also get you better customer service if things go wrong, and make returns easier/cheaper/possible.

Examples:
Ampere Time battery, $449.99 (Ampere Time gets a review by Will Prowse)
Chins battery, $439.99 (Chins gets a review by Will Prowse too)
Pionergy battery, $379.99 (I've never heard of this one)

It's a 50-100% mark-up compared to ordering direct from China but still less than the $700 you mentioned a couple of posts upthread?

Offline RonnyRonin

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Re: Sheddi's power bank build thread
« Reply #18 on: September 04, 2021, 04:41:55 PM »
Correct, that is still cheaper. On my local classifieds I tend to see higher end batteries (Renogy, Battleborn) and the 100aH ones seem to be consistently in the $700-800 range, and are larger and heavier than the aliexpress option.

I think for the $200 savings I will in fact roll the aliexpress dice when it comes time.
share your tobacco and your kindling, but never your sauna or your woman.

 

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