1973 Merc 650 Sparks W/O Batt???

[pjc]

Happy New Year All,<br /><br />Just received a switchbox from Ebay for this motor. Lucky me, I have sparks w/ batt connected and jumped between red and white at motor harness terminal. <br /><br />Sparks as described above w/ yellow/red's from (x2)stator disconnected from rectumfier.<br /><br />With yellow/red's connected to rectumfier and batt connected I have same sparks (yippie!!!)<br /><br />With yellow/red's connected to rectumfier and batt negative term disconnected I have no spark.<br /><br />Question??--is this normal for this motor as opposed to a mag. sparked Merc.? Or is minimum voltage required at pos. batt to make spark?<br /><br />Thanks and Happy New Year '04

 

[hondon]

Re: 1973 Merc 650 Sparks W/O Batt???

You have battery CD ignition and therefore need battery voltage to work.This switchbox is easy to fry by farting around and as you know, not cheap.SOO ,stop farting around until you get a Merc engine analizer, or advice to work around it.

 

[mellowyellow]

Re: 1973 Merc 650 Sparks W/O Batt???

ditto. u can fry the rectifier real fast without<br />a battery attatched.<br />good luck,<br />M.Y.

 

[rodbolt]

Re: 1973 Merc 650 Sparks W/O Batt???

hello<br /> why not just install it and run a spark test?<br /> those old switch boxes are not cheap. some are NLA from merc. dont play with it or you may find yourself looking for another. and lord help you if you roast the trigger assy.<br /> good luck and keep posting

 

[pjc]

Re: 1973 Merc 650 Sparks W/O Batt???

Thanks guys. I did measure the stator resistance between yellow/reds disconnected from rectifier. Used a digital and had 1.7 ohms. I understand I should be using an analog meter to measure stator. What resistance can I expect as measured?<br /><br />The crummy manual I have is real vague regards to testing electricals. Will wind up ordering one from Iboats if Lovely Bride cuts loose with some jing.<br />Any input for bench test of rectifier? I know it is little more than a diode. I believe my Fluke 77 diode function is fine for this test, but, what values can I expect?<br /><br />BTW, that Ebay switchbox is original Merc p/n 332-4796-A6. Looks like new, a bargain for $42, shipping included. I was dreading having to shell out $200+ for a Rapair aftermarket CDI. I do like the Rapair unit though do to CDI and coil all on one mounting plate.<br /><br />Another BTW--I was panicked when I discovered I had cracked the spring loaded carbon button in the distributor cap. Those caps are not cheap, and hard to find. Turns out that carbon button (brush) is a common ¼” motor brush-$3.50 at local True Value. Just had to shape the tip to slightly rounded where rotor contact is.<br /><br />Thanks again All,<br />Pat

 

[rodbolt]

Re: 1973 Merc 650 Sparks W/O Batt???

hello again <br /> the stator does not care whether you use an analog or digital. it is just a coil of wire. wow what a deal on a switchbox. I sell them used for 100-150 .use the money ya saved on the stator to grab the manual .I cant tell offhand what your stator resistance should be. 1.7 -6 sounds about right for that model. <br />good luck and keep posting.

 

[pjc]

Re: 1973 Merc 650 Sparks W/O Batt???

Thanks Rod. I am testing for sparks, etc. on the motor. I have the motor on a stand in basement for this work. <br />Photo of plugs is alum. plate I made to view sparks when pulling over motor w/ rope. Plate grounded to motor. Man, to say I was happy to see three fat blue sparks is an understatement.<br />Other photo is the Ebay switchbox-seller said did not know if it worked--would refund selling price if bad. Yippie--it works!!<br /><br />Any input on the rectifier rodbolt??<br />

 

[JasonJ]

Re: 1973 Merc 650 Sparks W/O Batt???

Pat, is your rectifier fried? I have always used bridge rectifiers from Radio Shack for less than $5 and they work fine. All a rectifier is is a glorified diode that converts the two directional AC output of the generator into the one direction of the DC operating system. No need to spend five billion dollars. I always bolt it to the aluminum bracket to transfer heat, and it works great. If I blow one, its another $5 and I am ready to go.

 

[pjc]

Re: 1973 Merc 650 Sparks W/O Batt???

Hello JJ, thanks for the tip. Do you have a RatShak p/n for the rectifier? Or specs?<br /><br />Happy New Year!

 

[mellowyellow]

Re: 1973 Merc 650 Sparks W/O Batt???

brand new merc rectifier is $35.<br />not to say a ratshack wouldn't work, but $35 is<br />about the cheapest marine part you can buy.<br />the dealer will also try to sell you a small<br />mounting bracket for $8 cuz the new style has a<br />different shape. make yur own...

 

[MrWick]

Re: 1973 Merc 650 Sparks W/O Batt???

I have had a problem measuring a trigger plate with a digital meter but when measured with a analog meter all readings were correct.I talked to a local outboard mechanic and he stated he recommends an analog metr to do resistance readings on merc electronics.He has seen in the past on stators and trigger plates that the digital meter did not read correctly.If you find wrong readings using a digital,I would round up an analog meter before replacing a part especially the expensive ones.That has been my personel experience.

 

[JasonJ]

Re: 1973 Merc 650 Sparks W/O Batt???

Ratshack only sells one bridge rectifier. It is about 1 inch square with an angle cut in one corner. It has four posts, two for AC, one for DC+, and one for DC-. Just make sure if you use one that it has a good heatsink, either by bolting the bare metal surface to aluminum bracketry and using dielectric grease to transfer heat, or make a small 2 inch square aluminum plate. Getting the Merc part is a good idea, but the ratshack trick works just fine.

 

[rodbolt]

Re: 1973 Merc 650 Sparks W/O Batt???

hello pat<br /> sometime tomorrow I will dig up my manual for testing the rectifier. I love my digital for testing diodes <br /> good luck and keep posting

 

[pjc]

Re: 1973 Merc 650 Sparks W/O Batt???

Thanks all for the replies,<br />Firstly, all tests done with all wires removed from rectifier.<br />Turns out rectifier is indeed shot. Diode test should return 0.5--0.7 or so volts. Fluke red lead to ~, or ac terminal, black test lead to DC+ terminal on rectifier. <br />Both ac (stator) terminals returned open when tested as above. One ac terminal returned short when black lead to powerhead, or ground--other ac lead returned open upon same test.<br /><br />Stator resistance between yellow/blacks = .9 ohm.<br /><br />JasonJ, I did check out the RatShak rectifier--$2.99 here. Specs are 25 amp max, 50 piv (peak in voltage??)<br /><br />I found used Merc one on fleabay, $10 plus ship-kinda like the RatShak deal though. <br />I have a short RatShak relay story--mice chewed insulation off 24 volt control wires of an outdoor airconditioner unit. Fried relay on PCB of furnace in condo--HVAC shop wanted $40 for relay--RatShak had same relay for $9 as I remember.

 

[hondon]

Re: 1973 Merc 650 Sparks W/O Batt???

You are testing charging components on a battery CD ignition system.If your batteries are fully charged and you have no ignition output,then you have a problem with[the completly separate] ignition system.

 

[pjc]

Re: 1973 Merc 650 Sparks W/O Batt???

Yes hondon, the ignition and charging system are indeed individual systems. And I do have sparks, after replacing switchbox.<br />The initial post was regarding will the ignition system make sparks w/o batt.--IE-say a person runs the batt down on the water. Not enough batt to turn starter. Will use of rope to turn over motor allow charging system to provide enough juice to make sparks, allowing motor to start. Not I believe. There must be at least 9 or so volts at the switchbox, provided by batt., to make sparks.<br /><br />Bottom line is--#1: keep the batt. in good condition on a batt. cdi system. #2: ensure that the charging system is functioning correctly.

 

[JasonJ]

Re: 1973 Merc 650 Sparks W/O Batt???

I ran my 1250 with a bad rectifier most of the season, the ignition system was only running on battery power. I would make sure it was charged before going out, and it always seemed fine. I finally got off my butt and did the ratshack trick, and with the charging system actually working, I gained about 400 rpm, and the motor ran noticebly better. The lesson I learned was that the Mercs really need all the juice they can get for peak performance.