Help, underwater 18v alarm

Thread Starter

Mally110

Joined May 2, 2020
9
Looking for some help and guidance on a personal project for my sport. I play underwater rugby, at international level, the referees in this use a cable operated buzzer system. Now this is a pain. I've designed a small(ish) remote buzzer that will remove all cables to the surface. My only issue is powering the damn thing. The buzzer in question is a sonitron sp7 that has an operating voltage of 0-36. So I've designed mine to use two 9v batteries in series. To make it waterproof, I would like to seal this as much as possible. So looking at making this a rechargeable affair, but this is where my knowledge of electronics ends. Would I need 9v charger or 18v? What do I need to stop overcharging them? Is it possible to fit them into a cylinder that has an I.d. of 32.5? I dont know what to expect from this as most things I've built is cnc tooling and dies for press shop so cad is no issue to me. If anyone can help or point me in a direction of somethi I need to buy or a very basic diagram (I'm not opposed to soldering) that would be very very much appreciated.
All the best and stay safe!
Ashley
 

Dodgydave

Joined Jun 22, 2012
9,666
The easiest rechargeable cells are Nicads, or Ni_mhis , they are only 1.2V per cell so you need to group several together. Next option is Lithium-ion or Life po cells, these need dedicated chargers and come in higher voltages, is that 32.5mm inside diameter??
 
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Thread Starter

Mally110

Joined May 2, 2020
9
The easiest rechargeable cells are Nicads, or Ni_mhis , they are only 1.1V per cell so you need to group several together. Next option is Lithium-ion or Life po cells, these need dedicated chargers and come in higher voltages, is that 32.5mm inside diameter??
So the square 9v batteries
The easiest rechargeable cells are Nicads, or Ni_mhis , they are only 1.1V per cell so you need to group several together. Next option is Lithium-ion or Life po cells, these need dedicated chargers and come in higher voltages, is that 32.5mm inside diameter??
I dont quite understand? By 9v I meant the square 9v batteries? If i put two of those in series i would get 18v correct? I dont think I need to get to 36v as it should be loud enough at 18v to hear the 15 or so meters apart we will be underwater.
 

Dodgydave

Joined Jun 22, 2012
9,666
Yes 9V in series is 18V, . The square Pp3 type rechargeable batteries are 8.6V..

Your main question for battery choice is how much current will you need to use, then how long will it be used for , this will give you the AH rating, for example if your system uses 100mA and you use it for 60Mins, that's 100mAh, .so choose wisely..
 
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Thread Starter

Mally110

Joined May 2, 2020
9
Yes 9V in series is 18V, . The square Pp3 type rechargeable batteries are 8.6V..
So I guess how would you charge two of these in series? What do I need? I'm guessing they wont need balancing but would a standard charger know when they are both full if i got an 18v charger?
 

Dodgydave

Joined Jun 22, 2012
9,666
You don't need balancing with nicads, 2 x 9V cells in series can be charged with an 18 to 20V adapter. You can leave nicads on tricle charge ..
 

Thread Starter

Mally110

Joined May 2, 2020
9
You don't need balancing with nicads, 2 x 9V cells in series can be charged with an 18 to 20V adapter. You can leave nicads on tricle charge ..
Well that makes my life so much easier!!!! Last question then before I annoy people too much. If I wished to put an led to signal that's its charging, could I put this across the contacts inside the buzzer with a suitable size resistor to stop it blowing or is that not how it works. I am sorry if this is really basic, there is.more to this as.id like to make a whole system that uses a microphone to listen for the buzzer and stops a timer and awaits input from the referees. But that's in the making.
 

Lectraplayer

Joined Jan 2, 2015
116
That does sound like an interesting project. The LED you proposed does sound like it would work, though you probably can also make a coil set to charge it inductively without ever having to open the device to charge it.

BTW: the square "9 volt" batteries in NiCd actually put out 7.2V, so running at 14.4V should work.
 

Thread Starter

Mally110

Joined May 2, 2020
9
Yes you can put a Led on wlth a Series resistor across the charge socket easily, .
Sweet thankyou so much. I started this idea with a very simple idea, then when I realised I couldn't just throw batteries in it and swap them out easily. I feared I'd hit an impasse with my limited knowledge. Thankyou so much for your help
 

Thread Starter

Mally110

Joined May 2, 2020
9
That does sound like an interesting project. The LED you proposed does sound like it would work, though you probably can also make a coil set to charge it inductively without ever having to open the device to charge it.

BTW: the square "9 volt" batteries in NiCd actually put out 7.2V, so running at 14.4V should work.
I did think about that, but have no idea how to do it. I thought about nfc charging too but again not a clue. But I wouldn't know where to put it. I can upload a photo of my design, I dont mind the length getting longer but dont really want to increase the diameter as it's all ready 38mm external
 

AnalogKid

Joined Aug 1, 2013
8,693
To be clear, is there anything else powered by the batteries, or is the whole project just battery > switch > buzzer ?

If that is the entire project, then consider an increase in complexity for an increase in convenience. Managing the charging of multiple batteries in series is not terribly complex, but it is a pain. Here is a way around that.

There are a ton of small electronic modules on ebay, and some of them are small boost converters. This is a power supply circuit that boosts an input DC voltage to a higher DC output voltage. The beeper draws a max current of under 14 mA, so a very small module can run at high efficiency. The upside is that the project now will run on a single battery - 3.6 V LiPo, 7.2 V NiCad, whatever.

If you want to build the circuit from scratch, I'd recommend a 555 driving a charge pump. If you want to wire up a pre-assembled and tested module, here is an example:

https://www.ebay.com/itm/DC-DC-Adjustable-Step-Up-Converter-2-15V-to-5V-28V-2A-Boost-Power-Supply-Module/383371409382?hash=item5942b777e6:g:NJoAAOSw1T1cB4pL&LH_BIN=1&LH_ItemCondition=3

ak
 
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Thread Starter

Mally110

Joined May 2, 2020
9
To be clear, is there anything else powered by the batteries, or is the whole project just battery > switch > buzzer ?

If that is the entire project, then consider an increase in complexity for an increase in convenience. Managing the charging of multiple batteries in series is not terribly complex, but it is a pain. Here is a way around that.

There are a ton of small electronic modules on ebay, and some of them are small boost converters. This is a power supply circuit that boosts an input DC voltage to a higher DC output voltage. The beeper draws a max current of under 14 mA, so a very small module can run at high efficiency. The upside is that the project now will run on a single battery - 3.6 V LiPo, 7.2 V NiCad, whatever.

ak
Finally logged in on the computer, Yes it will only be a simple buzzer switch batteries and the led to signal charging below is the cross section of it with buzzer at one end and button at the other(in red) i had planned on making it a twist cap to change the batteries but i think rechargeable will be better. if it is too quiet, what would be the next step in batteries? the buzzer is rated upto 36v1588451056268.png
 

Thread Starter

Mally110

Joined May 2, 2020
9
To be clear, is there anything else powered by the batteries, or is the whole project just battery > switch > buzzer ?

If that is the entire project, then consider an increase in complexity for an increase in convenience. Managing the charging of multiple batteries in series is not terribly complex, but it is a pain. Here is a way around that.

There are a ton of small electronic modules on ebay, and some of them are small boost converters. This is a power supply circuit that boosts an input DC voltage to a higher DC output voltage. The beeper draws a max current of under 14 mA, so a very small module can run at high efficiency. The upside is that the project now will run on a single battery - 3.6 V LiPo, 7.2 V NiCad, whatever.

Example:
https://www.ebay.com/itm/DC-DC-Adjustable-Step-Up-Converter-2-15V-to-5V-28V-2A-Boost-Power-Supply-Module/383371409382?hash=item5942b777e6:g:NJoAAOSw1T1cB4pL&LH_BIN=1&LH_ItemCondition=3

ak
sorry didnt see the rest before i replied. so this is what i was hoping that i could charge it from a laptop usb, so i could get a booster (like this one for example after a quick type) https://www.ebay.co.uk/itm/MT3608-P...sid=p2385738.m4383.l4275.c10&var=493201806173. that would mean i could then use a small hobby/model battery thats 3.6v or 11.1 v lipo that would reduce space but increase complexity, a little i think? correct?
 

Audioguru again

Joined Oct 21, 2019
2,061
I am glad that you decided not to use NiCad rechargeable batteries:
1) You have no proper charger circuit.
2) Cadmium is a deadly toxin and is banned in many countries. You do not want to swim in water that has a Cadmium product in it.
 

AnalogKid

Joined Aug 1, 2013
8,693
2) Cadmium is a deadly toxin and is banned in many countries. You do not want to swim in water that has a Cadmium product in it.
That would depend on the concentration, wouldn't it?

A 9 V NiCad battery is not all cadmium, and not pure cadmium. BUT, if it were, that would be 1.85 cu. in. of pure cadmium. Ground to a powder more fine than toner and stirred into an Olympic-sized swimming pool. The worst case (smallest) pool size is 3.5 m deep x 12 m x 8 m. That is 336 cu. m. or 20.5 million cu. in., for a concentration of under 50 ppb. That is 10 x OSHA limits, but an actual battery has around 1% cadmium by volume, so I think they'll live.

ak
 

Audioguru again

Joined Oct 21, 2019
2,061
Name Brand battery manufacturers do not make Ni-Cads anymore so if you find any, they might be old and leaky and made where poor quality products are made.
Even cheap Chinese solar garden lights cost only one dollar and do not use Ni-Cad batteries anymore.
You should use Ni-MH like they do.
 

Lectraplayer

Joined Jan 2, 2015
116
sorry didnt see the rest before i replied. so this is what i was hoping that i could charge it from a laptop usb, so i could get a booster (like this one for example after a quick type) https://www.ebay.co.uk/itm/MT3608-P...sid=p2385738.m4383.l4275.c10&var=493201806173. that would mean i could then use a small hobby/model battery thats 3.6v or 11.1 v lipo that would reduce space but increase complexity, a little i think? correct?
Personally, I would trust unscrewing it to charge the batteries more than trusting a USB port to maintain the seals, and making an inductive charging base doesn't sound that hard. Just maybe a section of pipe that your project just fits into with a coil at the bottom, and a coil at the bottom end of your project. Sliding the project into the base alligns the coils, then you just make sure you have enough energy to charge your battery like you want. ...though I may consider an 18650 battery with a charge manager and a boost converter for power.
 
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