Run this 1.5v pump from a 18650 battery

[Nicholas bray]

Hi I'm new to the forum

I was wondering would I be able to run this pump designed for 2 x aa batteries connected in parallel from a single 18650 battery which obviously has a higher voltage of over 4v fully charged reducing to 3.6 as the battery reduces in power

 

[Nicholas bray]

 

[Bluejets]

3 x !n5401 diodes (3 amp 100v) in series with the motor.

 

[Nicholas bray]

So its as simple as 0.7 voltage drop x 3 = 2.1v
3.6-2.1=1.5v ?

 

[Alec_t]

Are you aware that for safety reasons the 18650 battery needs protection from over-discharge?

 

[Nicholas bray]

I'm new to using 18650 batteries but I did read recently that running the battery until completely discharged can leave the than battery useless and you won't be able to recharge it is that what you mean ?

 

[Nicholas bray]

I have only used the batteries in my headlamp until now and haven't let it completely run out my kids have bought me a nitecore charger for Christmas as I don't trust the cheap charger that came with it

 

[(*steve*)]

Many cells are "protected" which means they have a cutout if the voltage goes too high or too low.

The limits are such that the cell should not explode, but the cell can still be damaged.

The easiest way to see if you have a protected cell is to measure it. The "protection" is a small PCB on the end of the battery inside the shrink wrapped cover.

An 18650 battery should be 65mm in length. If it is a few mm longer then this is most probably the protection circuit.

 

[Nicholas bray]

That's interesting to know I had some ultrafire batteries which came with the headlamp I know there are supposed to be alot of fakes around but I have to say once charged will run my high power torch for around 5 hours before the light dims a bit I'm curious to measure these to see how long they are

 

[Colin Mitchell]

" bit I'm curious to measure these to see how long they are"
They are 65mm

 

[Nicholas bray]

So no protection circuit

 

[(*steve*)]

So no protection circuit

Did you measure yours or did you take Colin's word for it?

Colin's pronouncements are not always to be taken heed of.

I went and grabbed some 18650 cells which measure about 66mm in length.

In addition to this, the cover of the cell has printed on it "Rechargeable battery with PCB", and "over charge and discharge protection" (amongst other things).

Do your cells have similar claims on them?

Regardless of the protection (or lack thereof) you should use a proper charger. There are many USB powered ones on eBay.

 

[Nicholas bray]

No not yet I've been to bed
lol
I have bought a nitecore charger which I've read is a quality one

 

[GPG]

PWM the motor, dropping the voltage is wasting power. How much current does the motor draw?

 

[Nicholas bray]

Sorry I don't know as I haven't bought it yet I'm trying to decide if ill be able to run it of a rechargeable 18650 before purchasing it

 

[Nicholas bray]

 

[Nicholas bray]

Would this circuit work ?
I tried to simulate running it from a battery and it failed due to lack of a ground
As soon as I run it from a vcc supply and included a ground it ran ok

 

[GPG]

Would this circuit work ?

Yes but it is wasting more power than the pump uses

I tried to simulate running it from a battery and it failed due to lack of a ground
As soon as I run it from a vcc supply and included a ground it ran ok

Simulators need a reference to crunch the numbers.

 

[GPG]

Info:
http://lygte-info.dk/review/batteries2012/Common18650Summary UK.html
http://batteryuniversity.com/learn/article/lithium_based_batteries