9v Battery Backup in line with mains adaptor?

[Foxinthehouse]

Hi everyone, I have a Toro garden water controller. It is a 9volt system operated by two PP3 batteries. With age the very thin wires on the battery connection have broken. It is in a shed so I have changed the batteries for a 240/9v adaptor. Works great and saves a lot in replacement batteries.
I now have a problem that during power cuts the controllers internal backup battery fails after a short time. So this is what I need some expert advice on.
The mains adaptor is rated 9v / 1500mA
A 9v PP3 is around 450mA
Would it be possible to add a PP3 battery 'inline' with the adaptor to retain power to the controller in the event of a power outage.
I am just a bit worried that the power adaptor may cook the battery or something.
Thanks for reading and any advice.

 

[Avo Mk8]

Would it be possible to add a PP3 battery 'inline' with the adaptor to retain power to the controller in the event of a power outage.
I am just a bit worried that the power adaptor may cook the battery or something.

I think you are right to worry. Don't just put a supply across an ordinary pp3 battery.

The way to do it is to have a 9v rechargeable battery connected to a compatible trickle charger, designed for continuous charging, and then take a supply from across that to your unit.

I see there are some mini 9 volt Uninterruptible power supplies about, intended to do what you want, for home routers or security cameras etc. That might be an easy but slightly more expensive option - it you can find someone with stock!

Mini UPS Uninterrupted Power Supply 7800mah with Output USB 5V 2A DC 9V 12V 2A: Amazon.co.uk: Computers & Accessories

Free delivery and returns on eligible orders. Buy Mini UPS Uninterrupted Power Supply 7800mah with Output USB 5V 2A DC 9V 12V 2A at Amazon UK.

www.amazon.co.uk

Hopefully someone will be along to recommend a little module and battery to do the job ?

 

[Foxinthehouse]

I think you are right to worry. Don't just put a supply across an ordinary pp3 battery.

The way to do it is to have a 9v rechargeable battery connected to a compatible trickle charger, designed for continuous charging, and then take a supply from across that to your unit.

I see there are some mini 9 volt Uninterruptible power supplies about, intended to do what you want, for home routers or security cameras etc. That might be an easy but slightly more expensive option - it you can find someone with stock!

Mini UPS Uninterrupted Power Supply 7800mah with Output USB 5V 2A DC 9V 12V 2A: Amazon.co.uk: Computers & Accessories

Free delivery and returns on eligible orders. Buy Mini UPS Uninterrupted Power Supply 7800mah with Output USB 5V 2A DC 9V 12V 2A at Amazon UK.

www.amazon.co.uk

Hopefully someone will be along to recommend a little module and battery to d

Thanks Avo Mk8: Good advice and I will work something out along those lines.

 

[DPG]

It's possible you may be able to do it with a couple of diodes, but I would err on the side of caution and follow avo8's advice.

 

[Avo Mk8]

It's possible you may be able to do it with a couple of diodes, but I would err on the side of caution and follow avo8's advice.

Actually I think the diode version would be worth trying!
I was thinking more along the lines of a maintained battery, but if it's just a 'sacrificial' one, and not required very often, or for a long time, this will do it, with the existing supply and the existing battery isolated from each other as above.

 

[Foxinthehouse]

Thanks for the good advice. So if I go along the lines of two diodes, I am capable of doing this as a DIY project, but could use some guidance as to the value of the diodes I need to buy for a 9v battery connected to a 9v 1500mA supply as this area is stretching my knowledge, but I would like to learn.

 

[Avo Mk8]

For clarification, I pinched this from the web!
Ignore the ref to 12v (it's 9v in your case), and the 100ohm resistor is your Toro.
Let us know if further info needed.



If you're not into soldering and using Veroboard etc. you can probably lash up the above on a chock block or equivalent! ?

 

[DPG]

For clarification, I pinched this from the web!
Ignore the ref to 12v (it's 9v in your case), and the 100ohm resistor is your Toro.
Let us know if further info needed.

View attachment 91579

Bet me to it! Was just googling the current ratings of the 1N... series.

 

[Avo Mk8]

Bet me to it! Was just googling the current ratings of the 1N... series.

Yup. The 4004 is notionally 1A, but seems happy with more! over 1v drop at 1.6A
Could use Schottky or something beefier, but to be honest I don't think it matters!

If the Toro product is designed with two PP3 batteries in parallel, that suggests peak current requirement in the 1A max region. However it's presumably got a motorised valve in it, which may take more, but is intermittent. My understanding is the mains adapter was not part of the Toro, but obtained by Foxinthehouse for his modification.

 

[DPG]

I'd go for 1N5404 - this is the 3 Amp equivalent.

 

[Foxinthehouse]

Well thanks guys. ?I wasn't expecting such a comprehensive answer and I am mightily grateful. I am going to used your suggestions and even do a solder job, which will test my skills as my soldering is about as good as my welding, functional but definitely not pretty.
Avo Mk 8, yes the Toro had two 9v pp3's in parallel. It actuates a solenoid to turn on the watering system so it is a very short burst and one battery is sufficient to operate it under test conditions, so I think the two batteries are purely for longevity of operation. You are right that the mains adaptor is my own addition after the battery wires sheared off right where they entered the controller. A bit of butchery to the case has left me with two useable stumps of wires to which I have soldered extentions. We are away from the property for long periods and that is why I decided to use the mains adaptor route. It was only after fitting the adaptor I realised a power cut would reset the clock and timings, as the battery model Toro, unlike the mains version , does not have a decent back up battery, just one that lasts long enough to change the batteries, if you are quick!
I will come back to report progress, but it may be a while as I am currently in Portugal and not sure where to purchase the diodes locally. (Brexit it has put paid to Amazon or eBay, but that is another story that could run and run under discussion).
Thanks again for increasing my knowledge of electronics.
Superb help from Avo Mk8 and DPG makes this forum the best around!

 

[Foxinthehouse]

Just an update as promised. Couldn't find the diodes locally in Portugal so had to wait for a friend who brought some out with him. Fitted them yesterday and it works a treat. Thanks again for your great advice. Will post a related enquiry along the same lines regarding my caravan solar panel.

 

[DPG]

Just an update as promised. Couldn't find the diodes locally in Portugal so had to wait for a friend who brought some out with him. Fitted them yesterday and it works a treat. Thanks again for your great advice. Will post a related enquiry along the same lines regarding my caravan solar panel.

Great stuff, thanks for letting us know!