Running a nav light from a Tohatsu 18 hp outboard - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 


Like Tree2Likes
Reply
 
LinkBack Thread Tools
  #1  
Old 08-20-2012
TQA's Avatar
TQA TQA is offline
Bombay Explorer 44
 
Join Date: Apr 2009
Posts: 2,632
Thanks: 0
Thanked 51 Times in 47 Posts
Rep Power: 6
TQA is on a distinguished road
Running a nav light from a Tohatsu 18 hp outboard

I have fitted a 12 volt nav light to my Tohatsu 18hp outboard and wired it up to the charging circuit. The bulb promptly blew the first time I revved the engine. [Never had this problem with my old Johnson.]

OK I understand that I have an unregulated AC output from the lighting coil. The Tohatsu manual suggests that I use an 12v 80w bulb. This is car headlight size.

Is there an easy fix eg

what about a 24 volt bulb?

what about an inline resistor say 33 ohms?

PS I don't need to worry about a picky coastguard measuring my light output in lumens where I use my dink.
Reply With Quote Quick reply to this message Share with Facebook
  #2  
Old 08-20-2012
zz4gta's Avatar
I don't discuss my member
 
Join Date: Aug 2007
Location: Chesapeake Bay
Posts: 2,446
Thanks: 0
Thanked 16 Times in 16 Posts
Rep Power: 8
zz4gta is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

And if you're motor dies and you're dead in the water, with no lights, what do you do then?

They make portable lights that run on batteries, pretty easy solution.
__________________
Merit 25 # 764 "Audrey"
Reply With Quote Quick reply to this message Share with Facebook
  #3  
Old 08-20-2012
tommays's Avatar
Senior Member
 
Join Date: Sep 2008
Posts: 4,275
Thanks: 1
Thanked 28 Times in 28 Posts
Rep Power: 7
tommays will become famous soon enough
Re: Running a nav light from a Tohatsu 18 hp outboard

No battery to keep things in control ?
__________________
1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #4  
Old 08-20-2012
asdf38's Avatar
Senior Member
 
Join Date: Jul 2010
Posts: 722
Thanks: 1
Thanked 8 Times in 8 Posts
Rep Power: 5
asdf38 is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

Quote:
Originally Posted by TQA View Post
I have fitted a 12 volt nav light to my Tohatsu 18hp outboard and wired it up to the charging circuit. The bulb promptly blew the first time I revved the engine. [Never had this problem with my old Johnson.]

OK I understand that I have an unregulated AC output from the lighting coil. The Tohatsu manual suggests that I use an 12v 80w bulb. This is car headlight size.

Is there an easy fix eg

what about a 24 volt bulb?

what about an inline resistor say 33 ohms?

PS I don't need to worry about a picky coastguard measuring my light output in lumens where I use my dink.
I'm not an expert in motors, magnetics or outboards but are you sure it's AC? Unless they expect an external rectifier and regulator that's pretty useless on a boat.

Assuming its DC lets run the numbers on the 33 ohms using an 80W bulb as an example. The 80 watt bulb would expect to draw 80/12=6.7A so it would have a resistance of ~12/6.7=1.8 ohms. So if you put that 33 ohm resistor in series you'll cut the current down to 12/(33+1.8)= 0.34A or 4 watts (12*0.34) but nearly 100% of those watts will be in the resistor. You'd have no light and a very hot (or very large) resistor.

So that's not a good option.

Obviously if you blew the last light bulb, assuming it was a good bulb and didn't just blow by coincidence then you had too much voltage. So yes a 24V bulb would be fine. This is much better than adding a resistor. A better option here would be an LED which are all current limited in some fashion which and likely to be rated for 12/24V operation already.

But finally, yes I agree with others. Get a battery powered LED combo nav light and carry a spare set of batteries.
Reply With Quote Quick reply to this message Share with Facebook
  #5  
Old 08-20-2012
TQA's Avatar
TQA TQA is offline
Bombay Explorer 44
 
Join Date: Apr 2009
Posts: 2,632
Thanks: 0
Thanked 51 Times in 47 Posts
Rep Power: 6
TQA is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

Hey maybe I need to explain further. The engine is on a dinghy. The VERY last thing I want to do is add more complicated electrickery AND a battery to simple dink.

I want to have the engine with it/s little white light as a self contained unit. I have done this before with a Johnson and just ran the 12 volt bulb straight off the lighting circuit with no rectifier or regulator.

The output from the charging coils is ALTERNATING CURRENT.

On open circuit and nr max rpm we get about 100 volts.

So what resistor bulb combination would work.

Would an LED work ? I did not think so as the max reverse voltage is about 5 volts and positive going is not that much higher?
Reply With Quote Quick reply to this message Share with Facebook
  #6  
Old 08-20-2012
Senior Member
 
Join Date: Jun 2012
Posts: 119
Thanks: 4
Thanked 0 Times in 0 Posts
Rep Power: 3
Bruce_L is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

Quote:
Originally Posted by TQA View Post
The output from the charging coils is ALTERNATING CURRENT.

On open circuit and nr max rpm we get about 100 volts.
YOW!!! :100 VOLTS, hope you are made of highly resistive fiberglass !!!

Seriously, 100 Volts??? Help me to understand, how/where did you make this measurement. What scale was the meter set to as well. Give us some facts and we'll try to help, but I'm all for a simple LED setup myself like others here.

Last edited by Bruce_L; 08-20-2012 at 08:29 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #7  
Old 08-21-2012
Learning to sail
 
Join Date: Aug 2010
Location: San Francisco Bay Area
Posts: 113
Thanks: 1
Thanked 2 Times in 2 Posts
Rep Power: 5
aaronwindward is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

I think getting a small lead acid battery might be the right thing to do, but I'm not sure if that's what's typically done. You could try a resistor, and maybe combine it with a large capacitor, but I really think a battery is going to work the best, and it will have the side benefit of giving you a little bit of light if your motor dies.

I think the right way to make a circuit is some sort of shunt thing with a diode and a resistor.
Reply With Quote Quick reply to this message Share with Facebook
  #8  
Old 08-21-2012
pvanv1's Avatar
Hinterhoeller HR28
 
Join Date: Nov 2007
Location: Hamburg and Wilson NY
Posts: 156
Thanks: 9
Thanked 0 Times in 0 Posts
Rep Power: 7
pvanv1 is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

Quote:
Originally Posted by TQA View Post
I have fitted a 12 volt nav light to my Tohatsu 18hp outboard and wired it up to the charging circuit. The bulb promptly blew the first time I revved the engine. [Never had this problem with my old Johnson.]

OK I understand that I have an unregulated AC output from the lighting coil. The Tohatsu manual suggests that I use an 12v 80w bulb. This is car headlight size.

Is there an easy fix eg

what about a 24 volt bulb?

what about an inline resistor say 33 ohms?

PS I don't need to worry about a picky coastguard measuring my light output in lumens where I use my dink.
What is your actual model of outboard? If you are not running a rectifier (available for the motor), you need to. Otherwise, if you have tied into just the alternator, you can produce some fairly high AC voltages. Likewise, you want a battery to stabilize the circuit.
__________________
Paul Van Voorhees
Certified Tohatsu TLDI Technician
Mgr, Obersheimer Sails
Buffalo, NY USA
Reply With Quote Quick reply to this message Share with Facebook
  #9  
Old 08-21-2012
asdf38's Avatar
Senior Member
 
Join Date: Jul 2010
Posts: 722
Thanks: 1
Thanked 8 Times in 8 Posts
Rep Power: 5
asdf38 is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

Quote:
Originally Posted by TQA View Post
Hey maybe I need to explain further. The engine is on a dinghy. The VERY last thing I want to do is add more complicated electrickery AND a battery to simple dink.

I want to have the engine with it/s little white light as a self contained unit. I have done this before with a Johnson and just ran the 12 volt bulb straight off the lighting circuit with no rectifier or regulator.

The output from the charging coils is ALTERNATING CURRENT.

On open circuit and nr max rpm we get about 100 volts.

So what resistor bulb combination would work.

Would an LED work ? I did not think so as the max reverse voltage is about 5 volts and positive going is not that much higher?
The bottom line is that the voltage at the bulb when operating must be less than the voltage it's rated for. There is no trick. While you say it may reach 100V I assume that this droops significantly under load (but now much load I don't know). If you really want to do this, I still think the easiest way is just try high voltage bulbs. An incandescent bulb is resistive so adding a resistor doesn't add much value. Unless you just don't have 24V or 48V bulbs on hand. The other variable is power. Assuming that the output voltage droops under load a larger load will cause it to drop lower. So a higher wattage 12V bulb may pull the voltage down to 12V and work fine.

I take back part of what I said about LED's. With 100V AC I don't think they are likely to work but again it all comes down to whether the voltage falls to an acceptable range for the particular module.

But again, this is all guesswork without knowing the parameters of the output (voltage, frequency, impiedence (how much it drops under load)).

@aaronwindward
A cap creates an RC filter which will lower the voltage in an AC circuit. But a resistor also lowers the voltage. The RC filter would also depend on frequency of the AC power with higher frequency equating to lower voltage. This is somewhat interesting because it might help cancel out the effect of voltage increasing at higher RPM's assuming the frequency is tied to that.

What your probably thinking of is a zener diode (or transorb) and a resistor. Zeners can clamp to a particular voltage by dumping all excess current (kind of like that emergency drain at the top of your sink). You'd need back to back Zeners in this case due to AC and a resistor would help handle excess power but specifying them correctly would mean knowing more about the output.


Anyway, this is way more detail than needed but it's the result of just not knowing what that output is. When I suggested battery before I meant AA's or D's or whatever. A handheld battery module with an LED can run for hours. What about a flashlight? Still a nice easy option.
Reply With Quote Quick reply to this message Share with Facebook
  #10  
Old 08-21-2012
TQA's Avatar
TQA TQA is offline
Bombay Explorer 44
 
Join Date: Apr 2009
Posts: 2,632
Thanks: 0
Thanked 51 Times in 47 Posts
Rep Power: 6
TQA is on a distinguished road
Re: Running a nav light from a Tohatsu 18 hp outboard

It is a 2012 Tohatsu 18hp 2st.

The voltage was measured OPEN CIRCUIT with a sensitive digital multimeter at the charging circuit outlet under the cowl.

The manual says this oulet will produce 80 watts at 12 volts.

I have done this sort of thing before and know that some combination of bulb voltage/wattage and resistor will run the bulb in its dinky housing on the top of the OB cowl. It is just that the trial and error method will be difficult and time consuming for me as I sit at anchor in a bay on the south coast of Grenada with no Radio Shack to hand.

I have seen other Tohatsus with this sort of set up so it can be done!
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Chineese Tohatsu knockoff outboard motor... SVDistantStar Gear & Maintenance 18 07-10-2011 02:27 PM
Running light configuration stiffwind Gear & Maintenance 35 04-09-2011 12:10 AM
steaming light, running light, wiring yzlian Pacific Seacraft 4 03-24-2011 09:44 AM
Small outboard charging systems. (Tohatsu/Nissan in specific.) lydanynom Gear & Maintenance 26 07-21-2010 10:56 AM
Deck and running light windmutt Jeanneau 1 12-31-2008 12:27 AM


All times are GMT -4. The time now is 07:05 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.