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Forum Index : Microcontroller and PC projects : 7.4v LiPo batteries?
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9643 |
Hi folks.  Does anyone have a good reliable source of decent quality LiPO battery packs? These are the ones that look like they are in a little silver coloured plastic bag, and normally come complete with a charging circuit sealed into the top of them, so all you have to do to charge them, is supply them with a suitable voltage, and the embedded charger circuit will take over charging the pack for you. Smaller is better, naturally, but will look at anything. 500mAh or so, 7v4 at least, as I need to regulate down to 5v or 3v3. Mr. Google has resulted in hundreds of links to places selling these, but I wondered if anyone here has used any and how much of a problem they had charging them etc because I believe they need special treatment as far as charging goes. I am also looking at the plethora of RC batteries now available for drones, cos they are the new in thing at the moment, so there are a ton of batteries for them to choose from - does anyone have any recommendation in that area? Smoke makes things work. When the smoke gets out, it stops! |
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palcal Guru  Joined: 12/10/2011 Location: AustraliaPosts: 1997 |
Hi Grogs, If I have unprotected cells I use something similar to these protection It will protect from overcharge and over discharge. Paul. edit. I have used the little flat camera batteries with these protection boards. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2948 |
Grogs, EDIT: re-reading your post - you may have been asking where to buy - hold on . . . (but in meantime here was my initial response): I would recommend you consider choosing one of the thousands of battery packs out there designed to recharge mobile phones 'on-the-go'. I designed a brilliant LiPo charging circuit for the first generation of School Computer BUT it cost a fortune. The battery was a 6000mAH (triple 2000mAH pack) and it had a fuel gauge with data outputted on an tiny OLED, and all controlled by a MM. Technically it was brilliant BUT it cost over £50 for all the components from mainstream component suppliers (Mouse, RS, E14, DigiKey, etc). Build this into a product and the cost of the product becomes too high. Using cheap 'modules' from 'you know where' was not sustainable; and certainly a big 'no no' in my eyes. I now use typically a 10,000mAH battery pack kicking out 5v and feed that into my MM circuit's 3v3 vReg. Then for charging the pack has a USB input which I take from a RPi 2.1A PSU. And the pacjks I use are ones with a built in display giving an indication of remaining charge. So can use readily available & branded parts (pack + PSU) for a cost of less than £20. (eBay less than £5 but not recommending cheap battery packs as some have been known to explode). Another thing - most people design the charging circuits incorrectly; sometimes with devastating results. Remember Sony laptops a while back, or more recently the Samsung Galaxys? Finally, the WiFi test you carried out for me from there in NZ was driving a MM driven by a such a battery Pack. WW |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2948 |
In the UK I buy battery packs 'on the high street' from either a mobile phone shop such as CarPhone Warehouse; or from a computer superstore (PC World). This is the model I like a lot - RRP is high, but when on offer it is half price!  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9643 |
I certainly remember the Samsung Galaxy disaster, and certainly don't want that. I will PM you about your charger circuit WW - it might be something I can adapt to what I need, and sounds like it is fully protected etc. Cost is not TOO much of an issue, more reliability and no fire-risk! EDIT: Had a quick look at that link WW(and Paul!), and the power bank thing is way too big. I need a battery that is about the size of a standard 9v battery - no bigger, or it will make the device to large to fit where it needs to be mounted. Smoke makes things work. When the smoke gets out, it stops! |
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| aargee Senior Member  Joined: 21/08/2008 Location: AustraliaPosts: 255 |
Have a look around Hobbyking... eg this You might have to look after your own charging/protection or there might be suitable batteries in there somewhere. For crying out loud, all I wanted to do was flash this blasted LED. |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
Seriously do not do it. Some LiPos although, not all, and most Lithium Ion batteries, come with protection circuits built in that are nothing to do with charge control. They are last ditch safety circuits to offer some protection against failure of the devices (where the battery is being used) own charge control and power control circuitry. For instance the low discharge voltage cutoff of these internal battery circuits is a frightingly low level of 2.4V, you do not want your battery to go as low as that, if it does you might want to bin it. For the device you would need to incorportate a safe cuttoff circuit that disconnects the battery when the voltage falls to 3.3V to 3.0V per cell. No point at all in running them lower than that as there is virtually no capacity left when the cells are that low. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9643 |
Acknowledged. I know that LiPo batteries have to be charged with a controller of sorts, not just the load resistor and trickle-charge arrangement you can get away with with the old NiCD's. Does anyone have any recommendations as to a LiPO charging arrangement or charge-controller chip or something like that I could look into? Whatever charger arrangement is to be used, it must be safe, and price is not really THAT much of an issue, safety and reliability are - do not want the Samsung cellphone fires problem....... Smoke makes things work. When the smoke gets out, it stops! |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1997 |
Hi Grogs, Have a look at this It's only a linear charger but I have been charging lipos that way for a long time with no problem. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
Those TP4056 chargers are fine for single LiPos and cheap as chips. Remember you need to change the charge resistor to reduce charge current to a safe level for the LiPo in question, 1A is way to much for a 500mAhr LiPo, 150mAhr is much safer. And those chargers are not so easy to use in a two cell setup. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
Well, can you get away with a 3v3 regulated supply as that is possible from a single LiPo with the right choice of low drop out regulator ? The charging for a single LiPo is a lot easier to arrange. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9643 |
@ Paul - Thanks for the link. @ srnet - I will have a look at the design. I MIGHT be able to get away with 3v3 design - the MM will be running at that voltage, it is the RF module that will probably want 5v or it won't want to work - I will check the datasheets some more. Assuming for the sake of argument that I only use one 3.7v LiPO cell, what makes it that much easier to charge that one cell over a couple in series? Sorry - LiPO batteries are NOT something I have had much to do with, only to know that there is really only one right way to charge them, and any deviation from that usually results in exploding batteries or fires etc, and I really don't need that!  Smoke makes things work. When the smoke gets out, it stops! |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
For a single LiPo you can use one of those TP4056 USB charger PCBs, they are around £2 for 10 delivered (yes I do mean 20p). It does not get much easier. Now for two LiPos your going to have to build your own charger circuit and of cource one that can detect the situation where only one of the cells goes bad. There is still then may be the issue of reverse polarity protection and low voltage lockout, but thats a different problem really. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4071 |
Just a thought but you might get ideas from some of the Olimex boards (e.g. PIC32 Pinguino OTG) as they support 3.7V Lipo and so on. John |
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