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Batteries

Discussion about Tx, Rx, Servo's, Batteries, Chargers, and all the other things we like to talk about..
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MDev
Posts: 122
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Batteries

Post by MDev »

I’ve brought some 18650 li on single cells to try, they will replace NMIH cells if they prove useful. I initially brought a couple and a charger along with holders. I don’t have any way of measuring the percentage of charge remaining, no doubt the industry will catch up with that? Two and three cells together seems the ideal size to power my gliders?

Anyone else going down this route? Can you charge two cells with a four cell charger?

M

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Cliff Evans
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Joined: 29 Dec 2019, 15:13
Location: Bristol
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Re: Batteries

Post by Cliff Evans »

These batteries are used in my Frsky TX. Not sure that I would use them in a model. I purchased a dedicated charger from Ebay. https://www.ebay.co.uk/itm/UK-Nitecore- ... SwdVZbctDA

harry curzon
Posts: 95
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Batteries

Post by harry curzon »

I use Jeti Power-Ions which is basically that 18650 cell, and I have also made my own from individual cells.
They are not a direct replacement for Nimh. They work at lipo voltage so you either need a regulator, or high voltage servos.
They must be charged using a Li-ion or Lipo setting. Normally their max voltage is 4.2V per cell, same as lipo. Older style Li-ion used a lower max V so the Li-ion charge program runs to a lower voltage, hence less fully charged if it is a 4.2V cell, and you will get quite a lot less capacity out of them than you expect.

Check the data sheet on your cells to find if they are 4.2V max or less.

MDev
Posts: 122
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Batteries

Post by MDev »

The ones I have here are Vapex 2600mah and the cover states they are 3.7v which I suspect is their voltage under load?

I see their are many other brands and unbranded on fleabay with many capacities, I’ve seen as much as 9800mah claimed.

M

harry curzon
Posts: 95
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Batteries

Post by harry curzon »

3.7V is the nominal voltage of a lithium reaction. The actual voltage under load could be higher or lower, it depends on the load and the state of charge. Older style Li-ion tended to have a nominal V of 3.6V and a max of 4.1V, newer Li-ions tend to have the same values as lipo, i.e. nominal 3.7V and max 4.2V. If I had an 18650 cell with nominal 3.7V then I would expect it to have max 4.2V but you really must check the manufacturer's specification because if for some odd reason it is max 4.1V then you run some nasty risks charging it to 4.2V. In other words, I am not going to take the risk of telling you that it is safe to 4.2V when I cannot absolutely guarantee it!

It is not safe to charge a 4.1V cell to 4.2V. It is sort of safe to charge a 4.2V cell to 4.1V, it is not going to be damaged, explode, catch fire etc., but that last 0.1V accounts for a surprising amount of capacity and you will get a lot less than 2600mAh out of it which might mean it goes flat considerably before you expect it to. The issue comes up on rc forums fairly regularly, people charge 4.2V 18650s using the Li-ion setting on their charger but on discharge get a lot less than the rated capacity and wonder why. The reason is that it is not fully charged, they need to use the Lipo setting.

You can get 18650 size cells to a little over 3000mAh capacity but anyone claiming 9800mAh is being, shall we say, optimistic! Like nicads and nimhs, the more capacity you try and squeeze in, the more you have to give up elsewhere such as reliability, C rating etc.

Ebay has lots of spare bedroom shops selling unbranded or even branded cells at low prices. They are cheap because they are old, worn out cells recovered from discarded laptop packs and vapes. That's fine to use in a vape, which is where the vast majority of the sales of those cells go, but I do not consider it safe to use for the control of an aeroplane. I tried such cells for a little while where I was using two batteries through a battery backer and thus had some redundancy, but it wasn't long until one cell suddenly failed completely. I recommend only buying brand name cells from a well established shop that has a reputation to maintain. That means they are expensive, but not half as expensive as losing control of an aeroplane!!

MDev
Posts: 122
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Batteries

Post by MDev »

Thanks Harry, I should be Ok with these Vapex ones from the Component shop then. It may be a while before I can test them at this rate. Still, more building time!

harry curzon
Posts: 95
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Batteries

Post by harry curzon »

Component shop should be able to tell you its max voltage for charging

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