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Author Topic: Simple DIY low battery voltage warning circuit  (Read 475 times)

Martin [Admin]

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Simple DIY low battery voltage warning circuit
« on: September 13, 2021, 12:30:23 am »


I've been looking for this circuit for years!
I used it in my Darnell British U class submarine, back in the 80's!.....

It flashes a LED as your battery drops below a set value, the lower it drops, the faster it flashes!    :o

From ETI Circuits magazine No.2 1978 - page 32
( Electronics Today International )


https://worldradiohistory.com/UK/Electronics-Today-UK/ETI-Circuits-No-2-1978.pdf









« Last Edit: September 13, 2021, 10:25:49 am by Martin [Admin] »
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Skimmer Fan

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Re: Simple DIY low voltage warning circuit
« Reply #1 on: September 13, 2021, 08:11:02 am »


I will have a go at this one.Could this circuit be modified to monitor other voltages.
Do you know if it would work on all types of batteries.
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Regards
Skimmer Fan

malcolmfrary

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Re: Simple DIY low voltage warning circuit
« Reply #2 on: September 13, 2021, 08:56:35 am »

I will have a go at this one.Could this circuit be modified to monitor other voltages.
Do you know if it would work on all types of batteries.
1 Yes.  One the operation of the circuit is understood.
2 Probably.  The original battery type is not stated, as the circuit monitors the fall-off in voltage, the warning time will be dependant on the voltage fall-off characteristic of a) that type of battery and b) the use it is being put to.


A potential problem with circuits like is is the availability of the more specialised semiconductors, like a unijunction transistor.
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roycv

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Re: Simple DIY low voltage warning circuit
« Reply #3 on: September 13, 2021, 08:57:24 am »

Hi you might find some of the components a bit difficult to find.  The 2N6027 programmable unijunction transistor is an old item although you can buy 30 of them for 6 on ebay must be old stock disposal.  This is the flasher device.

The BC107 could be any NPN couple of hundred millivolts transistors.  Have you noted that there is no mention of C1 and C2?  I went to the link and the circuit there does not mention them either.
They are electrolytics but C2 is in the timer circuit for the flasher so a value would be useful.  The Zener diode is not critical could be within half a volt either way.

I agree it is a nice little circuit there is an updated one using Op Amps but handling them needs care re-static.
I would build on Veroboard but try it out on a breadboard first.  Let me know if the values are found for the capacitors.
I used to make my own BEC's until they were a standard circuit inclusion in an esc.  Just a few components a zener and a power transistor, all on Veroboard and still use them with the old type esc's.

Well done Martin finding this circuit.

Regards
Roy

Roy
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roycv

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Re: Simple DIY low voltage warning circuit
« Reply #4 on: September 13, 2021, 09:05:22 am »

Hi Malcolm the first paragraph says it is to monitor 4 pen light cells, I assume AA batteries or 6 volts in all.
regards
Roy
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Martin [Admin]

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Re: Simple DIY low voltage warning circuit
« Reply #5 on: September 13, 2021, 09:53:31 am »


Now you mention it, I do seem to remember an addendum or contacting ETI and asking for values....

I've even found a photo of the circuit board I built!
It's on the right-hand side of the Vero board, the left side is another voltage monitor circuit using a 8211 chip.
( The left circuit uses a 1uF cap (light blue) .... looks the same doesn't it? .....so maybe 1uf  & 4.7uF / 10uF ?!? )


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roycv

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Re: Simple DIY low battery voltage warning circuit
« Reply #6 on: September 13, 2021, 11:20:04 am »

Hi Martin you are probably right with values, but what is an 'extra flash now and again'. 

I used to take ETI mag. but about that time I was buiilding my own model railway controllers, I remember a lovely one with multiple switched acceleration and braking rates. and a 'squirt circuit' for giving a recalcitrant engine to start up.  Still working. 

But the modern can motors start up very nicely on a low voltage so in the, not used box now along with my capacitance meter, servo tester, SLA battery charger and an own design tachometer based on 555's.
The only circuits currently in use (with a fellow modeller) is my water level controller circuit design.

Gone over to Guagemaster now with a lifetime guarantee.
Regards
Roy
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roycv

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Re: Simple DIY low battery voltage warning circuit
« Reply #7 on: September 13, 2021, 12:39:36 pm »

Hi Martin I tried to print the circuit diagram and circuit info off but could not.  If it is possible and what do I do?
Roy
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Martin [Admin]

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Re: Simple DIY low battery voltage warning circuit
« Reply #8 on: September 13, 2021, 12:54:40 pm »


Try this Roy .....

« Last Edit: September 13, 2021, 01:53:43 pm by Martin [Admin] »
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Martin [Admin]

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Re: Simple DIY low battery voltage warning circuit
« Reply #9 on: September 13, 2021, 01:46:43 pm »


 Getting obsessed now!








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roycv

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Re: Simple DIY low battery voltage warning circuit
« Reply #10 on: September 13, 2021, 03:28:20 pm »

Thanks Martin while I was trying to print my printer was having a bad day, I eventually switched it off and on again as I was taught when I was learning electronics!  I now have more than a few copies of the circuit!
Roy
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Circlip

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Re: Simple DIY low battery voltage warning circuit
« Reply #11 on: September 14, 2021, 08:58:36 am »

Now how small could that be using SMDs?  %%


   Regards  Ian
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C-3PO

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Re: Simple DIY low battery voltage warning circuit
« Reply #12 on: September 14, 2021, 10:25:26 am »

For the grand sum of approx 1.50 you could have a solution using the components pictured below

AA battery is just for size comparison, the resistors are not the actual values you would use



Regards
C-3PO
 
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roycv

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Re: Simple DIY low battery voltage warning circuit
« Reply #13 on: September 14, 2021, 01:58:38 pm »

Hi 3-CPO, the fish does not look too battered just wondering about the chips.  I take it you will not be using solder or the circuit board?   MMMM. has icloud got down to this level?

Have you got or can refer a circuit to us please?
Best, Roy
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Martin [Admin]

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Re: Simple DIY low battery voltage warning circuit
« Reply #14 on: September 14, 2021, 08:21:33 pm »

For the grand sum of approx 1.50 you could have a solution using the components pictured below

AA battery is just for size comparison, the resistors are not the actual values you would use


Regards
C-3PO
 


    ....... AND?!    <*<


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