12v bilge pump question

[Hadenough]

I have 10hp Tohatsu outboard on my RIB tender. I want to fit a 12v bilge pump but do not want to have a battery. Idea is to run it off the 12v output of the outboard. I have three "spare" wires under the outboard hood, one black on its own and a white and a yellow together into a two pin plug. Questions are: Is this a 12v output and if it is can I run an electric pump directly from it? I realise that this means that I will only be able to run the pump when the outboard is running but that will do me. Don't have the outboard with me at the moment so can't test the output with my multi meter.

 

[lw395]

Depends what Tohatsu model.
Not much info on Tohatsu.com, but you can download the user manual, which suggests a rectifier is an optional extra for the 9.8 2T model.
A lighting coil of 12V 80W is also an option.
But your model might be different.
Rule 500 bilge pump only takes a 2.5 Amp fuse, so I would expect it to run happily from the 12V 80W, but that will be unregulated, so with such a small draw might get more than 12V.
I suggest measuring it!
The volts might be quite high at no load and high revs, but will fall when loaded.
I expect the pump will tolerate a bit of over voltage, but there are limits!
You can get regulators intended for motorbikes, but they may not work reliably with no battery.

 

[Hadenough]

http://www.tohatsu.com/tech_info/own_man_pdfs/Toh9-9D2_15D2_18E2.pdf

I've found the manual, p51 shows the wiring diagram for my model. So, I see the white and yellow lamp outlet can I not just connect to this? You've guessed I suppose that electrics is not my best subject.

 

[lw395]

http://www.tohatsu.com/tech_info/own_man_pdfs/Toh9-9D2_15D2_18E2.pdf

I've found the manual, p51 shows the wiring diagram for my model. So, I see the white and yellow lamp outlet can I not just connect to this? You've guessed I suppose that electrics is not my best subject.

If you can identify, the 'battery' wires they should be DC.
The 'lamp' wires are AC.
I would measure the volts and check that it's not more than 14 or so at tickover, connect the pump and watch the volts as you increase the revs. Have a fuse in circuit. IF the volts climb above 15 with the pump running, stop.
You have to accept there is a chance of blowing up the pump with this sort of thing, having a small motorcycle battery in place would help.
You can use the lamp wires, if you add in a 'bridge rectifier' to convert AC to DC. You can get that from Maplins or similar. but it looks as if you already have a rectifier built in.

 

[Hadenough]

Thanks both I'll get it in the workshop and do some testing as described.

 

[markdj]

It will not work, you WILL require a battery and probably at least a 50Ah one...

The output from the outboard will be unregulated and with no battery will climb to 16volts burning out your pump. If you fit too small a battery the voltage will still go too high.

 

[William_H]

It will not work, you WILL require a battery and probably at least a 50Ah one...

The output from the outboard will be unregulated and with no battery will climb to 16volts burning out your pump. If you fit too small a battery the voltage will still go too high.

I would tend to disagree and at the price of bilge pumps I would try it out without battery.
A motor is not like a lamp in that the current will not rise as the square of the voltage because the motor will increase in speed generating more back EMF which limits current flow. Of course more current at higher voltage but not as much as you might think. If OP is concerned, put a lamp in parallel to load up the supply so reduce voltage. good luck olewill

 

[yoda]

Why not just get one of these:

http://www.ebay.co.uk/itm/All-makes...gineParts_SM&hash=item564a89d5c2#ht_500wt_715

You will then at least have a DC output which you can either use to charge a small battery or try the pump on.

 

[pvb]

I've found the manual, p51 shows the wiring diagram for my model. So, I see the white and yellow lamp outlet can I not just connect to this? You've guessed I suppose that electrics is not my best subject.

You can't use the white and yellow wires - these are an AC output. You need a rectified DC output for a motor.

It will not work, you WILL require a battery and probably at least a 50Ah one...

The output from the outboard will be unregulated and with no battery will climb to 16volts burning out your pump. If you fit too small a battery the voltage will still go too high.

He needs a rectifier first, to convert the AC into DC.

I would tend to disagree and at the price of bilge pumps I would try it out without battery.
A motor is not like a lamp in that the current will not rise as the square of the voltage because the motor will increase in speed generating more back EMF which limits current flow. Of course more current at higher voltage but not as much as you might think. If OP is concerned, put a lamp in parallel to load up the supply so reduce voltage. good luck olewill

It wouldn't work, the white and yellow wires are AC output.

 

[lw395]

Why not just get one of these:

http://www.ebay.co.uk/itm/All-makes...gineParts_SM&hash=item564a89d5c2#ht_500wt_715

You will then at least have a DC output which you can either use to charge a small battery or try the pump on.

That's one of these
http://www.ebay.co.uk/itm/KBPC3502-...al_Components_Supplies_ET&hash=item43aa77f0ad

which is a lot cheper, plus a couple of leads.

If the regulation is a real issue you could look at one of these:
http://www.ebay.co.uk/itm/BSA-NORTO...71?pt=UK_Motorcycle_Parts&hash=item4ab2a1f6f7
But I would enquire to see if it's ok to run that without a battery.