Thermistor Selection for TP4056: NTC Resistance Guide

[Trevo]

I'm thinking about buying a tp4056 and I'm wondering what thermistor I should buy. I looked at the data sheet and it said a [STRIKE]new[/STRIKE] NTC but that was it. So I went online to find one and I noticed they have resistance and I don't know which one to get. Could someone help me figure this out?

 

[Trevo]

When I said new I meant ntc.

 

[mabauti]

consult the tp4056 datashhet.

basically you need the operation point(s) of thermistor's resistance

 

[davenn]

consult the tp4056 datashhet.

basically you need the operation point(s) of thermistor's resistance

The datasheet isn't specific about the type of thermistor etc

Actually, all it indicates is that it makes use of the thermistor that is already part of the battery pack

cheers
Dave

 

[sophiecentaur]

The thermistor needs to be integral with the battery so it knows the temperature reliably. You don't need to buy one; it's there already.

 

[Trevo]

Where is it?

 

[sophiecentaur]

Where is it?

You would expect to find more than two contacts in the battery. The thermistor would be between two of them.

 

[Trevo]

I don't think we are talking about the same battery. What battery are you talking about?

 

[davenn]

show us a pic of YOUR battery and also a datasheet for it would help too

As I said in my first post, the thermistor is usually incorporated as part of the battery

Dave

 

[Trevo]

Datasheet for the battery?

 

[sophiecentaur]

Datasheet for the battery?

Yes. Or at least a picture of the contacts.

 

[Trevo]

There's the battery and datasheet

 

[sophiecentaur]

I see, now. We have been at cross purposes. I (/we) were assuming that you were talking of the type of LiIon battery pack you get in cameras, mobile radios etc.. These are in a (8V or whatever) pack with their own protection circuitry included and sometimes have several contacts on the sealed pack which interface with the 'special' charger. They usually cut off when the volts get low and cannot be recharged without opening the case or getting at them in some way.
Energiser (the company) supply their own chargers which will be their own design and may or may not include your charger IC. The value of the thermistor will probably be difficult to find out without opening up an Energiser charger and trying to read the legend on the side of the thermistor (probably some obscure number) and the IC may well have a similarly unhelpful type marking on it. They probably don't want you to copy their unit.
The chargers that come with electronic gear are also probably full of components with weird numbers on - and for the same reason. The manufacturers of batteries and chargers are not interested in being helpful - unlike the manufacturers of chips who want to sell them to as many people as possible.
LiIon batteries are a bit dodgy to charge if you don't have the right information about them. I'm sure it's not really as bad as all that but I would be inclined to do the charging in a suitable box to contain any leaks or explosions, during the experimental stage.
I just wonder if it's really worth while trying to save on the cost of buying a ready made charger. The Energiser ones are pretty cheap.

 

[Trevo]

I'm not really trying to save money on a charger in teeing to make a portable cellphone charger. When is out of battery I want it to be able to charge at someone's house with a usb. It's for accessibility not for a cheap way of charging. So you're saying that I cannot charge those batteries with the tp4056?

 

[sophiecentaur]

You have a cellphone with those Energiser Cells in it? That's pretty unusual, I think.

 

[Trevo]

I messed up. I am making a cell phone charger with those batteries in it. Those batteries will recharge the 3.7v li - ion battery in the phone.

 

[sophiecentaur]

OK. So why not charge those energisers with an energiser charger and avoid a lot of aggravation? The phone will take care of itself as long as you give it some volts. Though, charging as fast as possible needs some cleverness in the USB connector, I believe. I remember getting my knuckles rapped when I referred to USB type charging as a 'trivial' exercise.
There's more of the black arts than you realize here, I think. You just don't know enough about the battery characteristics to do this safely.

If you are at someone's house. won't they have mains for a mains phone charger? Personally, I'm all for an easy life and that sounds like the ideal solution. Now, if you were camping in the wilderness . . . . . .

 

[Trevo]

Well I was hoping to put in a solar panel also and the reason why I want a usb port for charging is because sometimes I'm at a friends house and we go somewhere. So for convenience I want it to charge at my friends house. Not everyone has a battery charger.

 

[sophiecentaur]

I know it's up to you and some projects are just fun to do but you could just as easily carry a mains charger as your battery charger. It is true that a nice fat source of DC charge would extend your talk time usefully, at times. I still think the DIY solution for the Energiser charging could be more of problem than you imagine. All the things you need are actually off the shelf (and not very expensive either).

 

[Trevo]

Ok so I want to build this. Talking to you had put a little doubt in my mind. So my question is if the tp4056 will charge the ultimate lithium batteries safely?

 

[NavinRJohnson]

I personally wouldn't mess with a DIY or e-bay board for a lithium battery charger, ESPECIALLY if I'd be using at at a friends house.
I know the lithium iron you're using are safer but, I've seen and heard about too many Li/Po fires that might make me a bit paranoid.

2 personal friends have had major fires.
One, crashed his plane at the flying field and threw his plane in his trunk to head home. Lipo was damaged enough in the crash it must have shorted in his trunk and set his car a blaze on the highway.
Friend two, lost his garage, 2 cars, motorcycle, tools, etc. when his son set the charger wrong for an RC car battery that was charging on the work bench.
Local RC clubs usually require all lithium's are placed in approved fire bags or boxed when charging at their facility. Again, these are Lipo which are a bit more prone to overheat and out gassing when charging.

If you don't get an answer if your cells are safe to charge with that circuit and still decide to go through with the project. Make SURE you charge them in a safe place the first few times to make sure all is well.

Good luck with the project!

 

[Trevo]

Well my box is an altoids tin so I think that will be fine and that's my whole problem. That's my original post question about which thermistor to use. If I put a thermistor then it detects if the batteries overheat and the top 40 is designed to shut off power when the cells overheat. So I'm wondering what thermistor to use.

 

[jim hardy]

So my question is if the tp4056 will charge the ultimate lithium batteries safely?

The Energizer literature for "Energizer Ultimate Lithium" L91 batteries says in two different places that they are not designed to be recharged.
Is that the battery you propose to recharge? It's the one for which you posted datasheet.

Product safety sheet here

http://data.energizer.com/PDFs/lithiumirondisulfide_psds.pdf page 2 of 4

Charging:
This battery is manufactured in a charged state. It is not designed for recharging. Recharging can cause battery leakage or, in some cases, high pressure rupture.

and Application Manual here
http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf page 15 of 18

and from Design Considerations here
http://data.energizer.com/design_hints/pages/dhints_seriesparallel.html

Installation of Dissimilarly Discharged Batteries
Batteries connected in parallel should be at the same state of discharge. If batteries at different states of discharge are installed into a device using a parallel battery configuration, the battery with the higher voltage will charge the battery with lower voltage until voltage equilibrium is reached in the system. This charging could lead to leakage, elevated temperature, or other damage to the lower voltage cell.

What you propose is risky business . I think you should buy rechargeable batteries instead.
http://www.energizer.com/batteries/rechargeable-batteries/Pages/power-plus-aa.aspx

http://www.energizer.com/SiteCollectionImages/Batteries/Energizer%20Recharge%20Power%20Plus/tab2-recharge-aa.png


old jim

 

[Trevo]

Wow didn't Reed the label. Thanks that would have been bad. So worth these batteries would the tp4056 charge those safetly?

 

[jim hardy]

Here's Energizer's doorway to technical information.
http://data.energizer.com/

NiMh has different voltage than LiIon so i don't think your 4056 is the right gizmo. Your datasheet says charge voltage is fixed at 4.5, yet also says it's for single cell? I don't understand that.

 

[Trevo]

I know it's for single cells that's why I wanted a thermistor so if something happens then it would shut off

 

[sophiecentaur]

I know it's for single cells that's why I wanted a thermistor so if something happens then it would shut off

But you didn't get Jim's point that a single cell is not 4.5V?
I really think you should learn more about this business before you explode one of those cells in your face. I would not touch one with a barge pole until I know a lot more than I know now, about those things.
There are so many other projects that don't involve spraying yourself with hot nasty chemicals.

 

[Trevo]

I'm not charging a single cell I'm charging 4 batteries. What I have learned is the only thing bad about that it if 1 dies then 1 or 2 batteries is getting the full
Force of the charger. The reason for the thermistor is if a cell dies the thermistor will air off the circuit when the batteries get hot.

 

[sophiecentaur]

Like I said. You really don't seem to know about this business to be safe. Do you know the true function of the thermistor? Do you know how four cells in series will behave if one of them is faulty?
You don't seem to want to take our advice so I am out, I'm afraid. Sorry

 

[Trevo]

I'm taking your advice. I'm sorry that you don't think so. I have just thought about the things you have said and telling what I have come up with to solve it.

 

[sophiecentaur]

And how do you know it will solve it?

 

[Trevo]

I don't know if it will that's why I have been asking you guys questions cause obviously you all are smarter than me.

 

[sophiecentaur]

OMG. So we're too smart to get involved.
Some people just won't be told.
In the end this is a safety issue and PF has rules about that.

 

[Trevo]

Am I missing something I never said you guys were too smart. I don't know how that's possible. I want to be safe also its just I want it to work and I'm asking how to do that.

 

[jim hardy]

well i learned a couple things from all this

first one was re-learning an old lesson - that being always start from a GOOD source of information, avoid imitations.

Secondly, apparently there is a 3.6 volt Li-Ion chemistry
and here's a charger IC made for it
http://cds.linear.com/docs/en/datasheet/4050f.pdf

which i think is better written than that one from Nanjing
because it gives detail about their "Temperature sensing " pin

The thermistor is connected from NTC (pin 2) to ground and is biased up by an internal 28.6k trimmed thin film resistor that connects to VCC through a P-channel MOSFET. This MOSFET also biases an internal resistor string to ground, from which voltage thresholds of approximately VCC/2 and VCC/8 are derived.
The NTC pin is compared to these thresholds by two comparators that have wired-OR outputs. The thresholds are selected such that an overtemperature condition will occur when the thermistor resistance is less than approximately 4.1k and undertemperature condition will occur
when the thermistor resistance is greater than approximately 28.5k. These correspond to thermistor temperatures of 50°C and 0°C for the specific type of thermistor listed above (many others will be close enough for most purposes).

I suspect the TP4056 is a knockoff of that Linear Tech device, and i avoid foreign knockoffs.
And i would NOT assume the Nanjing chip uses the same thermistor.
In other words, get your parts from a known reputable source.

OP needs to familiarize himself with Li-Ion charging
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

and make doggone sure he gets cells that are designed for recharging
and make doggone sure his contraption behaves, that is it applies correct voltage and current for his particular cells,
and make doggone sure it shuts down at expected temperatures.

Trevo - if you don't have the test equipment to do this, ie a good DMM and a good thermometer,
buy something ready made.