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9v battery to 4.3v output without the heat!!

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Al Chemist

New Member
Hi all, my first post here and I'm fairly new to electronics so be gentle.


I want to use a rechargeable 9v battery (Energizer HR22) to replace the supply from a cheapo 4.3v (+/-10%) Li-Ion battery.

Current Specs for the 4.3v Li-Ion are...
Maximum Discharge Current = 600mA
Maximum Charging Current = 450mA
Charging Current = 300mA
Typical Capacity = 320mA
Minimum Capacity = 300mA

Fully charged the Energizer HR22 is putting out 9.43v

I've tried rigging circuits using the LM317 variable voltage regulator, but it generates too much heat and the voltage changes rapidly with temperature fluctuations.

I'm thinking of using Zener Diodes and a resistor but the max power is a little high for standard 4.3v Zeners according to my calculations based on 600mA +10% for the maximum rating. (Although it could be argued 320mA + 10% is a more likely figure to aim at, over capacity seems sensible.)

So what I'm looking for is a small circuit, that will give me 4.3V +/- 10% 320mA from a 9v battery with very little heat output.

Any suggestions and pointers welcomed.

Thanks in advance, and sorry if this has been covered elsewhere here, I couldn't find anything when I searched.
 
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Wp100

Well-Known Member
but it generates too much heat and the voltage changes rapidly with temperature fluctuations.
Think you must have a problem with that circuit - the LM317 is a tried and tested device.

You want to drop 5v, at 320ma, so most things will generate heat to dissipate that amount of energy.

Perhaps the simplest way would be to use a series on 1amp diodes 1n4001/6

You do not say what you are supplying the power to , does it actually take 320ma, thats a massive load to put on a small battery.
The figures you are quoting as just the maximum for the battery, nothing like the typical loads it would have to supply if used on a phone.
 

audioguru

Well-Known Member
Most Helpful Member
The absolute max allowed voltage of a rechargeable lithium battery cell is 4.2V. If it is charged to a higher voltage then it will probably catch on fire. If you do not limit the charging current then it probably will catch on fire.

A rechargeable lithium battery cell is nominally 3.7V because the 4.2V charge quickly drops to 3.7V then the voltage drops slower to 3.0V when the load should be disconnected.

A little "9V" Ni-MH battery is actually 8.4V and can supply 320mA for about 10 minutes when its voltage will be 5.5V.

What do you have that needs such a high current?
 

Al Chemist

New Member
The absolute max allowed voltage of a rechargeable lithium battery cell is 4.2V.
My mistake I must been having a bad day when I measured 4.3v, and I've based all of my calcs on it.. duh!! :rolleyes:

Sorry I'll start again.. measured output from the battery fully charged is 3.82v

Stats for the battery are on the attached .pdf

It's only a small helmet camera, a mate asked me to look at as the battery runs down very quick around 15 minutes, it should last over an hour. I didn't imagine it had much consumption at all.

It's similar to this.. I can't find the actual unit.. MiniDV MD80s Peanut Sports Camera



The LM317 got very hot (hot enough to burn you), and I wanted to avoid a heatsink, by blowing on it I could raise the output voltage LOL!! That may have something to do with me trying to supply the camera with 4.3v, I'll try it again with 3.8v.

(over to the desk..... )

Which I just did, at 3.8v and it works without overheating, it's barely warm to the touch.

Thanks guys.. looks like you've hit the nail on the head in one easy query.. well done.

PS
I'l be back mooohaahhaaa ;)
 

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MikeMl

Well-Known Member
Most Helpful Member
...
The LM317 got very hot (hot enough to burn you), and I wanted to avoid a heatsink, by blowing on it I could raise the output voltage LOL!!
...
A chemist should know about the Laws of Thermodynamics :D

If you are dropping (9-4)=5V across the regulator; and the current through it is ~0.3A, there is no escaping that you are dissipating 5x0.3=1.5W. If you use a T0220 LM317 it might just about dissipate 1.5W if it is hanging out in free air, but if you stick it inside something where air cannot circulate past it it is going to get so stinking hot that it will shut itself down.

Now tell us that you were using the TO92 plastic package version of the LM317 :confused:
 

audioguru

Well-Known Member
Most Helpful Member
HR22 is 8.4V nominal and drops to 5.5V after 30 minutes @ 350ma drive current (1C).
where did you find the European datasheet for Energizer's 9v Ni-mH battery?
I didn't know it is made in Germany. Their Ni-MH single cells are made in Japan.

There are differences in the European and American datasheets for the 9V battery:
1) The voltage of the European one drops much more and quicker when the current is 17.5mA, 35mA and 87.5mA.
2) The European voltage curve at 350mA looks wrong.

The datasheets look different because the European one shows the older 7.2V/150mAh (6 cells) Ni-mH battery while the American one shows the newer 8.4V/175mah (7 cells) one.
 

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Hero999

Banned
Drop the 9V battery - it's a silly idea.

What is the minimum and maximum voltage requirements for the device you're powering?

You'll get more battery life from three AA cells and you won't need a regulator circuit.
 

Speakerguy

Active Member
I just googled for it, I didn't realize I had grabbed the European version datasheet.

Specifically I googled for HR22, which is what the OP said he had. I guess he is in Europe? Doesn't list a location.
 
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