1974 merc 85hp does is it suppose to charge the deep cycle batterys

[arthur1988]

im wondering if the motor charges the battery or is it different than a cars charging system cause asoon as i take the posative cable off the battery it turns off any help would be helpfull thxs

 

[jerryjerry05]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

Shoud include serial#/model etc!
It should charge any battery.
Sounds like the rectifier is shot.
When I was a newbie (1983)I bought a used boat.
I hooked up the battery cables backwards and blew the rectifier and it wouldn't charge.

 

[Chris1956]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

If that motor has a distributor, it will have battery driven ignition. You can ruin the ignition and rectifier by disconnecting the battery when the motor is running. Ignition parts are hundreds of dollars to replace.

The stator and rectifier combo should charge the battery. However, the rectifiers generally break when the battery cables are disconnected when the motor is running or connected backwards.

 

[Georgesalmon]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

Although I didn't disconnect my battery while running the engine. I might have if there was not a warning on the motor. I recently used this forum to learn about and fix a problem with my motor and ended up replacing the rectifyer with a rect/regulator with much success. Anyway, if you fried your rectifyer I might have a good used one for you. Don't know if a 79 1/2 115hp merc is the same but if it is you can have this one for the cost of postage. I'll never use it.

 

[Chris1956]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

George, Your old stock rectifier is the same function as his. His will be the older larger style, but yours will work fine.

BTW - I actually replaced my stock Merc rectifer with a 25A full wave rectifer from Radio Shack. They are less than $5 and never burn out.

 

[arthur1988]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

i mean the motor runs great just drains the battery should
it be able to run stereo and some other little things ??

 

[arthur1988]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

will a 25A full wave bridge rectifier work??

 

[Gibbles]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

I would love to hear more about the 25A Radioshack rectifer, but per the merc manual the rectifer is designed to burn out to protect both the switch box and the stator from damage if the battery connection is disconnected or loose.

but @ $30 a pop, the $5 one sounds like a good alt.

 

[merc850]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

A deep cycle battery is not recommended due to the hi amps required to charge it won't be supplied from from your alternator. Just use a maintenance type marine starting battery.

 

[Chris1956]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

Gibbles, I do not see how the rectifier burning out protects anything, as it is wired in parallel to the switchbox. The stator is just a coil of wire. Not much to burn out there.

The merc rectifier is simply a standard full wave bridge rectifier. The negative DC connection is grounded internally to it's case. The Radio Shack rectifier has four connections. You must ground the - connector, and then connect the stator wires to the AC connectors and the battery wire to the + connector.

 

[Gibbles]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

Gibbles, I do not see how the rectifier burning out protects anything, as it is wired in parallel to the switchbox. The stator is just a coil of wire. Not much to burn out there.

The merc rectifier is simply a standard full wave bridge rectifier. The negative DC connection is grounded internally to it's case. The Radio Shack rectifier has four connections. You must ground the - connector, and then connect the stator wires to the AC connectors and the battery wire to the + connector.

Yeah I was noting what my manual said (factory mercury)
possibly mainly the switchbox from getting the spike if the connection came loose?
who knows.

My 650 had the same problem, but caused by the main connector rotting and the rectifier fried.

 

[Moody Blue]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

i mean the motor runs great just drains the battery should
it be able to run stereo and some other little things ??

Your motor's ignition system depends on the battery voltage. No battery = no ignition. The only purpose of the charging system is to charge the battery so that the ignition system functions.

Your motor should be charging the battery, and will quite effectively run most any small electrical devices like stereo's, fish finders, VHF radios, lights etc. Before spending any money, find out why or if the battery is not being charged or not.

Using a voltmeter/multimeter, measure the battery voltage at the battery terminals with the motor off. Should be somewhere between 12V and 13V. Next, start the motor and run at a fast idle, say, 1500 rpm and measure the battery voltage again. You should be reading between 13V and 15V. If not, either the rectifier is dead or the stator windings or stator wires under the flywheel are defective. Those old motors are notorious for bad wiring.

There are many threads here on how to test the rectifier. In the interest of preventing very costly repairs, you should never disconnect the battery while the motor is running.

 

[Gibbles]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

I have been running my engine without being charged

I bought the jumbo deep cycle battery from Costco labeled as deep cycle\starting battery

I can run all day long with it, the engine trickles juice off, and I monitor the battery with my fish finder voltage readout...

If I get down to a 12v reading I call it a day, but I have been out there for 8+ hrs at a time with 0 issues

That said, I have parts on order

Only reason why I risk it is because I have a kicker on there that can get me home...

Not saying it's right but my merc manual (from the late 70's) says to never use sealed batteries due to the unregulated charging system.
Goes on to say you need to be able to add water back to the battery as it will cook off.

Test the stator wires from the under the flywheel, you should show some AC current, something like 12+v (I could have that way off as I'm trying to go off of memory)

 

[Georgesalmon]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

I paid $75 for my new rect/reg on ebay. It's new and a Mercury part. I just felt (right or wrong) that I wanted to use a merc recommended part that was actually put on later year engines with the same stator. Makes me feel all warm and fuzzy. I have read here that a lot of people are using the radio shack one with success so I would not discount that as a good idea. As above though you should test what you have. We all throw bunches of money at our boats and should spend what we have wisely on stuff that is really bad. That stator has only a 9 amp capacity, but it is enough to do a little more than just keep up with the motor ignition. I have a kicker to but I still like my main engine to be able to keep up it's own battery. It would take me a long time to get back from 10 miles out in Lake Michigan on 9.9hp in 20mph winds, lol

 

[Gibbles]

Re: 1974 merc 85hp does is it suppose to charge the deep cycle batterys

Yeah 10+ miles out, I would not even think about running a radio if my battery was not charging.

it would be a long drive back with a little kicker + a head wind