inverter for outboard

C

chi-girl

Well-Known Member
Joined
6 Jul 2011
Messages
205
Location
chichester
Visit site
in my new to me 15hp mercury 2stroke of 1985 vintage ive just found an external socket and traced wires back to top of engine i presume there is no inverter. is it a simple job of adding an inverter and joining a couple of wires fitted together to make 12v dc
Thanks Annie
 
An inverter converts DC to AC. You need something that does the opposite which is a bridge rectifier. Put a multimeter on the leads to check there is not one included as standard.
If the output is AC you need the rectifier. They are available from electronic stores. Look for something that's rated at as high a current and voltage as possible. Don't forget a fuse close to battery end.
Be carefully with a fully charged battery, particularly if the battery is small, that the battery voltage does not rise too high as you will not have a regulator.
The output from many outboards is small, but some models put out enough to helpful, at least at crusing revs.
 
Last edited:
A rectifier is what you need, not an inverter. Many motorcycle parts cane employed to fir an outboard. It is possible that this is just a lighting coil so may not have enough capacity to charge a battery....
 
Please check that the output is in fact AC. If the leads come direct from under the flywheel then it probably is.

If its DC the leads will be colour coded to indentify whicc is positive and which is negative and you should be able to locate a rectifier
I think a dc output would have leads to run to a battery rather than a socket for a plug

If its an electric start engine I'd expect it to have a DC output for charging the battery.

Assuming you find that it is AC then a bridge rectifier such as KBPC10005 from Maplin should do the trick 50volt and 10amps max or KBPC2501 100 volts and 25 amps max (a little over £2)
You could of course buy the proper part for I'd estimate about £40-£50

This is a similar one from RS which I used to use as a rectifier with an outboard that only had an AC lighting coil output ( mounted on a bit of aluminum as a bracket and heat sink)

DSCF1082.jpg
 
Last edited:
Rectifier for outboard motor

A s said you need a rectifier. I would suggest however that you buy 4X schotky diodes which have a lower forward volt drop loss. This means that you will get more DC voltage out of the motor hence more charge current into a battery. This assuming of course that it is just a "lighting coil" rather than a battery charger.
http://www.altronics.com.au/index.asp?area=item&id=Z0042
This is the biggest i can find from local (Oz) suppliers to give you an idea. You will need 4 of them unless like a Johnson O?B you have 3 wires from 2 coils. in which case you need 6 diodes.
The bridge rectifier made of 4 diodes consists of taking one wire AC and connecting an anode of one diode and cathode of another diode (The end with the band or head of arrow). The diode with the cathode not connected becomes the +ve output the end with the anode not connected becomes the -ve output.
The other 2 diodes are connected in similar manner tot he other AC wire so 2 cathodes connected go to +ve DC output and the 2 Anodes become -ve DC output.
If you then consider that if the AC output of the engine becomes +ve on one wire so -ve on the other the +ve and _ve become steered via the diodes to come out on the appropriate wires to the battery. When the polarity of the AC wires swaps the current is steered via the other 2 diodes to again appear as correct polarity DC to the battery.
You will notice however that current must pass through 2 diodes regardless of polarity. using ordinary silicon diodes will drop .7 volt regardless of current through each diode so total 1.4 volts or more lost in rectifier. The schotky diodes have a volt drop of more like .25 volts so total .5 volt lost which is much better when voltage may be a problem in pushing a charge into a battery. (you need around 13 to14volts DC)
So I suggest give the schotky type a try. rated at only 3 amps might be a problem and if they are blown through too much current be grateful. I can onlky get about .3 amp out of my o/b with ordinary silicon diodes. I have made up a schotky pack of 6 but haven't had the chance to test it yet. I expect more like 1 amp. (which might indicate to you that the exercise is not worth doing) good luck olewill
 
On the other hand if you are not into DIY electronics it may well be that you can obtain a "battery charging kit" for the engine from your Mercury dealer

Ron Hale in Portsmouth

Home Marine in Emsworth YH

Adrian Cronk Marine in Chichester

IMS Marine in Aldingbourne


It 'll cost a bob or two but should , if available, include rectifier to fit directly on the engine, all necessary wiring and connectors and all the screws to fit.
 
if the concensus is i will make max 1amp then it seems pointless. i was hoping for 6amps like my new 25hp tohatsu. is it possible to find the plug that attches to a 12v light string and add this plug on the end that goes into the 12v ac socket on the front of the outboard.

maybe a cpuple of 12v ac lamps to have a little light onboard as this appears to be the max useful current use.
 
davidpbo said:
At cruising revs I get about 4 Amps from a Mercury 8 HP 1989 with the charging coil and Mercury rectifier.
Click to expand...
I used to get similar, about 5A,from a Yanmar 8 HP 2 stroke circa 87 but the models do vary some put out much less.
 
chi-girl said:
if the concensus is i will make max 1amp then it seems pointless. i was hoping for 6amps like my new 25hp tohatsu. is it possible to find the plug that attches to a 12v light string and add this plug on the end that goes into the 12v ac socket on the front of the outboard.

maybe a cpuple of 12v ac lamps to have a little light onboard as this appears to be the max useful current use.
Click to expand...

I'd expect a good deal more than 1 amp max.

I get ( in theory) 4 amps from my 6 hp Evinrude of a similar age but the output is very dependent on the engine revs.

You should be able to get a plug from Mercury dealer maybe elsewhere

Is there any information in the owners manual?
You should be able to down load a copy from the download center at http://download.brunswick-marine.com/download/main;jsessionid=105vjo07c1lcd?type=corp if you have mislaid the original.
 
Last edited:
chi-girl said:
if the concensus is i will make max 1amp then it seems pointless. i was hoping for 6amps like my new 25hp tohatsu. is it possible to find the plug that attches to a 12v light string and add this plug on the end that goes into the 12v ac socket on the front of the outboard.

maybe a cpuple of 12v ac lamps to have a little light onboard as this appears to be the max useful current use.
Click to expand...

If you just want to run lights of it then you don't need a rectifier. Ordinary filament bulbs will work with either AC or DC. but you would need to make sure that your bulbs are big enough to use whatever power would be available form your engine. Too big and they'll be dull. Too small and they'll blow.

BUT you won't be able to run LED lights of it...they need DC.

I would expect to get around 4 to 6 amps from the coil of an engine of that vintage
 
chi-girl said:
4-5 amps would be enough to run a mobile charger and a radio vhf. looks like I'll go the rectifier route as i have a spare 85amp/hr battery
Click to expand...

If you have the battery then basically your bibs and bobs will run off the battery. The outboard will recharage the battery via the rectifier.

Because it's not regulated the volts output from the engine can be quite high. Because the volts can be high Id suggest you don't run your stuff directly from the engine without the battery being connected.

........ doing that was how I damaged my autopilot years ago. Very careful now!
 
You must log in or register to reply here.

Other threads that may be of interest

geem
First 6 months with no gas onboard
2 3
Replies
41
Views
1K
Baggywrinkle
Baggywrinkle

Share this page

Top