Using electronics with my unregulated outboard

[nickjaxe]

Hello all I have a 16ft dory type boat fitted with a 55hp yamaha BE origin outboard from about 1991, as far as I know going by the handbook the alternator has no regulator, I think it puts out about 17 volts last time I had a volt meter on it, so at the moment for my sounder\ vhf \ gps I run them through a seperate battery not linked to the engine so hence it dont get charged and I have to trickle charge it at home, the thing I was wondering what kind of voltage will these things be ok to, I know the gps is ok to 40 volts but not sure about the others, I would like to do away with the second battery and run everything off the one battery, hope sombody can enlighten me.

Regards Nick in cheshire.

<hr width=100% size=1>

 

[charles_reed]

Nick fit a rectifier to change the ac to dc (you'll only get half the output) and then feed that into the battery.

Fitting a fully fledged regulator would be a more correct, but more expensive and complicated solution.

<hr width=100% size=1>

 

[whiteoaks7]

Charles, I don't know where you learned your electronics but if you rectify the a.c. you can get more then the (rms) voltage depending on the configuration of the rectifier.

Don't do it! I think the answer to this problem is the fact that the instruments are only going to draw a small amount of current and so all that's needed is a small regulator - less than an amp I guess - which then feeds the instruments directly and throw away the battery. Try RS components or Maplin as sources or look on the web for basic electronics circuits under 'series regulator'. A suitable regulator chip would be a 7812 so check out a data sheet for this device (WWWRS.COM) and you may find a circuit for rectified/regulator that will solve your problem.

<hr width=100% size=1>

 

[charles_reed]

Thanks for that correction - no doubt to a purist my suggested course is anathema.

Having run an outboard recharging a battery on my boat for 4 years in the 60s, I can assure you that the voltage stays well within the instruments' range and gives you the benefit of some charge for other domestic uses and, equally convincing, the cost of the rectifier are minute.

<hr width=100% size=1>

 

[steve_cronin]

My experience too Charles. Unless the battery is of very small capacity it will smooth the input via the rectifier from the "lighting coils" of the flywheel magneto. Shunt regulators are available which just run excess charge into a diode arrar on a massive heatsink and I fitted one once when I was relying on the output from a Honda outboard. It failed after possibly only a short time due to salt corrosion but even then no harm was done to the electronics,

Now running the electronics directly from the rectifier without the battery in parallel would be a cause of serious damage.

Steve Cronin

<hr width=100% size=1>

 

[chriscallender]

Nick,

Does the engine manage to charge a battery just now without boiling the acid or overheating/overcharging it? If so, then it will be OK to connect instruments to that charging battery (properly wired and with fuses) If the battery is not really hot it doesn't have such a high voltage across the terminals. Like others have said do not connect the instruments straight to the engine without the battery being included in the circuit. In that cause since its unregulated anything could be happening although in all likelyhood the instruments would be robust enough to survive anyway... I had a car where the regulator packed up and battery overcharged, nothing electronic was broken.

Charging at 17v would seriously fry a 12v lead acid battery so I believe that under any measureable load the voltage must be dropping a lot from the 17v you measured, presumably with no load at all connected to the engine. Or else its not suitable for battery charging at all which I find hard to believe on a 1991 50 HP engine which is presumably leccy start - even my 1984 7.5HP Mercury could charge batteries.

Chris
<P ID="edit"><FONT SIZE=-1>Edited by chriscallender on 13/08/2003 13:54 (server time).</FONT></P>

 

[nickjaxe]

Thanks everybody for your replies, the engine is electric start, chris the batt gets warm when running and yes it was no load when I checked the voltage, had a look in the manual the engine lighting coil\alt is in the book as 12volt 80watt and has a full wave rectifier with 4 diodes, I am puzzled why they dont put a regulator on these engines, as I say the batt does get warm when running but I dont know if its to warm or not, I leave the boat at anglesey so next time I go down to it I will put a load to the batt engine running and see what the volts are then.

Regards nick in cheshire.

<hr width=100% size=1>

 

[William_H]

Nick you say the alternator is rated at 80 watts which is about 6 amps . Thats the max capacity of the alternator.. When you have a flat battery you may find 6 amps going to the battery but this will lessen as the battery charges and the voltage of the battery rises to around 14 volts. So at most you would only get 1 or 2 amps charge into a charged battery and most reasonable sized batteries can take that if not continuously then certainly for longer period than you can run the motor. Thats why no regulator. The sign that the battery iss being overcharged is that the water will be boiling off and will need frequent top up. If you check the battery voltage and find it less than 14 after a long run you will have no p[roblem running the electronics fron that engine battery.

<hr width=100% size=1>

 

[coco]

A good solution (albeit not the cheapest) is to use a 4 stage PWM regulator like the ones used for solar panels. It will definitely protect your battery quite well (no need to worry about boiling and gasing) and avoid any voltage spikes. Look at http://www.morningstarcorp.com/

<hr width=100% size=1>

 

[nickjaxe]

Thank you to for your replys looking at all the ideas

Nick

<hr width=100% size=1>