relay to power a 12v bilge pump

[KrisBlueNZ]

In that case you can use a "low dropout" (LDO) regulator. These can work with as little as 0.5V voltage difference between input and output, sometimes even less, so you could go down as low as 9.5V before the output voltage loses regulation.

How much current does the controller need?

Do you have a preferred supplier? I linked to Maplin before, but there's also Farnell / Element 14...

 

[cheagavara]

hi kris, it says on the tech sheet that the detector current consumption in ready mode is <10mA and in contact with water <90mA

maplins is good for me as we live on the isle of wight and for some reason people on the mainland (10mins by hovercraft and 15min by ferry) seem to think we are remote location even though we have one of the largest post office sorting centres here and every parcel company has a depot here. maplins however has a largish shop here.
most suppliers on the mainland suck air through theire teeth followed by "ohhh island of wight, posting there will come under out lying islands like the scotish highlands and will be expensive.......truth is royal mail is bound under legal contract to deliver to ANY address in the UK for the same price and we also have around 100 vehicle ferry crossings a day via 3 routes that opereate 23 hours a day, at peek times some of the routes operate a half hourly service so remote is not a word i would use lol

 

[cheagavara]

would I be able to just use something like this
http://www.amazon.co.uk/VvW-Waterpr...TF8&qid=1398710373&sr=8-46&keywords=12v+to+9v

or

http://www.amazon.co.uk/Converter-M...UTF8&qid=1398710588&sr=8-1&keywords=12v+to+9v

just a thought

 

[KrisBlueNZ]

OK, that's a pretty small current requirement.

The two items you linked to are both overkill - they can supply several amps, and they are switching regulators, which are designed for high efficiency.

The first one specifies an input voltage range of 11-28V so it has a dropout voltage of 2V. If the input voltage drops below 11V the output voltage will drop below 9V. Actually you can probably go lower - down to 10.5V, maybe lower - because you won't be drawing much current from it.

The second one doesn't specify a minimum input voltage but I expect it would be about the same.

They're both more expensive than an IC (integrated circuit - silicon chip) LDO regulator, but they would be easier to work with, and probably more rugged. Also, Maplin don't have a suitable LDO regulator IC. So they might be a good choice.

In any case, the water detector will probably work fine with voltage less than 9V.

In other words, the best answer is not clear :-(

I think you said that the water detector prefers 9V to 12V. Why do you say that?

 

[cheagavara]

"I think you said that the water detector prefers 9V to 12V. Why do you say that? "
this is what it said on the information leaflet. the leaflet is a bit awkward to read as although it says its made in Germany the leaflet looks like its been translated from Hebrew.
it says 9v to 12v but in the blurb it says it is "best suited at 9v operation"
if you think I would be better off with LDO regulator IC then I will source one online no prob,
so i will go back over previous reply and look at farnell again

 

[KrisBlueNZ]

OK. Yes, I think an LDO would be the best option. Farnell have four suitable devices. Listed in increasing price order:

Texas Instruments LM2940T-9.0: http://uk.farnell.com/texas-instruments/lm2940t-9-0/ic-v-reg-ldo-9-0v-2940-to-220-3/dp/9493514 GBP 0.76; 1A output current; 0.5V dropout; TO-220-3 package

Texas Instruments LM2940T-9.0/NOPB: http://uk.farnell.com/texas-instruments/lm2940t-9-0-nopb/ic-ldo-volt-reg-9v-1a-to-220/dp/1559442 (same but lead-free package)

Rohm BA09CC0T: http://uk.farnell.com/rohm/ba09cc0t/ldo-fixed-9v-1a-to-220fp-3/dp/2342851 GBP 1.58; 1A output current; 0.3V dropout; TO-220-3 package

Rohm BA90DD0WT: http://uk.farnell.com/rohm/ba90dd0wt/ldo-fixed-9v-2a-to-220fp-5/dp/2342850 GBP 1.90; 2A output current; 0.45V dropout; TO-220-5 package.

They're all suitable. I recommend the first one. It needs two decoupling capacitors: one from input to 0V, and one from output to 0V. The output capacitor is a bit critical; it must be at least 22 µF with an ESR (effective series resistance) between 0.1 and 1.0 ohms. This one is suitable: http://uk.farnell.com/nichicon/upw1v470med1td/capacitor-alum-elec-47uf-35v-20/dp/1818653. Another identical capacitor can be used as the input decoupler. They must be connected as closely and directly as possible to the regulator pins.

 

[debe]

Ive had 2 different yachts & found the simplest system for automatic electric bilge pumps, is use a pressure switch from a dish washing machine. It doesn't draw any current in standby, & works very well. I originaly got the idea from a commercial fishing boat. A far more reliable system in a salt water environment, as the pressure switch can be mounted high in the hull. If your using a pump that draws considerable current then add a relay to the system