New guy with charging voltage question

[halfor]

Stuck again, I have been attempting to install a tach on the 78 mercury 700. And it has been a PITA, after a few setbacks (type of tools to install, harness, rectifier, and wire rot). I installed the new Radio Shack rectifier, and started the motor to see if I was back to running ? charging condition. The good news was the rewire / splicing seems to work because it started. But I am concerned with charging voltage I read 16.6 at idle with muffs on. Searching this site leads me to believe it?s too high, should be more like 14.5?? The part was the one suggested here, the install was drilled and taped to old location so heat sinking should be good, I cannot find any mention of a regulator for my motor, does anyone else who did the Radio Shack mod have the same issue? is it a issue?. It was too late to try to see if the voltage would increase with throttle, assuming it would is this too much charging voltage? I am hopefully going to pre-test the tach tonight before I cut the hole. I?ll put muffs on and see if it works at idle and then rev it some to see if I get any response on the tach as well as check voltage at the batery.

Thanks

 

[Shawnee]

Re: New guy with charging voltage question

[I installed the new Radio Shack rectifier, and started the motor to see if I was back to running ? charging condition. The good news was the rewire / splicing seems to work because it started. But I am concerned with charging voltage I read 16.6 at idle with muffs on. Searching this site leads me to believe it?s too high, should be more like 14.5?? The part was the one suggested here, the install was drilled and taped to old location so heat sinking should be good, I cannot find any mention of a regulator for my motor, does anyone else who did the Radio Shack mod have the same issue? is it a issue?. It was too late to try to see if the voltage would increase with throttle, assuming it would is this too much charging voltage? I am hopefully going to pre-test the tach tonight before I cut the hole. I?ll put muffs on and see if it works at idle and then rev it some to see if I get any response on the tach as well as check voltage at the batery.

Thanks[/QUOTE]

Hi
I am new here and am not familiar with "the radio shack mod" but I do have an electronics background. 16.6 does sound too high. You will want/need to monitor this voltage, preferably with a separate volt meter (ie not the dash one) at the battery and see what the voltage does as engine speed is varied. If the voltage varies from say 14 ish to over the 16 you saw, then I would say a Regulator is not working. There should be one somewhere in the electrical wiring. I will go look for this rectifier mod to see what it is all about. At that voltage, there is a chance of over charging. Just my $.02

 

[Chris1956]

Re: New guy with charging voltage question

Shawnee, His OB charging system is unregulated. The entire charging system is a stator around which magnets rotate, inducing an AC voltage. This is run thru a full wave rectifier and fed to the battery. Obvious the voltage and current increase with RPM. Since the entire system is about 9A, regulation is usually unnecesary as the battery acts as a load.

Merc sells a full wave rectfier for about $50. Radio Shack sells a much better one for <$5, hence the "RS mod".

The tach is designed to count the stator pulses. It is therefore connected to one of the yellow stator wires.

 

[Texasmark]

Re: New guy with charging voltage question

Not having measured the dc output of a stator without a regulator I will forward what I recall from the site:

Unregulated alternator output: 16-16.5 volts at nominal speed....for an alternator idle can be considered nominal.

Regulated output: 14-14.5........

A fully charged battery measures 12.75 for me. To get the battery to charge, you need to supply more voltage than it needs to overcome losses and pull it up to the fully charged condition. Obviously when the battery is discharged and connected to the engine charging circuit it cannot put 14.5 volts across the battery. The current is limited by the capacity of the charging circuit and on a highly discharged battery the current requirement usually far exceeds the capacity thereof so with limited current, the voltage has to drop. Then as the battery starts filling up, it's current requirement reduces, comes in line with the capacity of the charger and the voltage rises to the full charging level. As the battery comes up to full charge the current finally drops to a trickle and after charging the residual voltage on the battery will be high....maybe 13.5 volts but as the chemicals in the battery stabilize, the voltage will drop back to the fully charged level.

In answering overcharging without regulation, I'd say that depends upon how long you run the engine without using any battery power, how big the charging circuit is, the battery size, and how discharged was it when you started. In short, yes it can happen, but I never blew a battery as a result....boiled some water out sometimes, but never did any damage. If it were any kind of a problem, OEM's would add regulators to all rectifiers.....would be too much flak from customers otherwise.

HTH,

Mark

 

[halfor]

Re: New guy with charging voltage question

Battery is a Wal-Mart everstart 24ms (I think), only electronics are starting and trimming, never tried the lights yet, and with some luck a tach. I had just pulled the battery off of a battery tender.

 

[j_martin]

Re: New guy with charging voltage question

Actually, without a load this rectifier only system will put out about 90V at WOT. The battery is the "regulator" in this case. That is why you never disconnect a battery on a running engine. It will wipe out everything connected instantly.

High voltage indicates battery failure, either sulfated, low electrolyte, or plate damage from being low on electrolyte.

With a good battery, frequently topped off with distilled water, the system works well and voltage will stay below 16, typically below 15 with a new battery.

hope it helps
john

 

[halfor]

Re: New guy with charging voltage question

Thanks, makes sense to me, however the battery is new, I felt bad having run it a few times without charging so I put the battery tender on it the night before. If I am following what you are saying, this set up will somewhat over charge the battery boiling the water, causing me to pay closer attention to the water level, but over all a perfectly fine way of calling my charging problem fixed?

 

[Chris1956]

Re: New guy with charging voltage question

Halfor, The charging system will put out a max of 9A, at WOT. With a decent 24 series battery and no electricity-using devices running, it may overcharge slightly, but that is not an issue. Check the water every 6 months or so, and fill when necessary.

 

[Texasmark]

Re: New guy with charging voltage question

Halfor, The charging system will put out a max of 9A, at WOT. With a decent 24 series battery and no electricity-using devices running, it may overcharge slightly, but that is not an issue. Check the water every 6 months or so, and fill when necessary.

Sounds good to me....the fine print says don't buy a sealed battery for a non-regulated charging system...Yea verily they do a better job of retaining their fluid "with regulated charging systems".....but yours is not such and you need to do as Chris says if you want the answer you were seeking.

My 2c,

Mark

 

[mr 88]

Re: New guy with charging voltage question

Over voltage will fry your switch box. Engine was made when they had the old standard vented batteries and that is what you should use. If you cannot find one or insist on using a low or maintenance free battery you should swap on a rectifier with a built in regulator.

 

[Shawnee]

Re: New guy with charging voltage question

Chris1956, thanks for the clarification. I am just venturing into the world of boating and have been enjoying these threads. You all seem really helpful and respectful. Nice to see on a forum. I purchased a 2000 Legend Sportfish 178 with a 1994 Mercury 90. It has some issues but rather than reposting common issues, I am going to stumble around with it for a while. There is a lot of information here so the reading will not be wasted time. Thanks for that.

As for the regulator info, I would suggest a resettable fuse (circuit breaker in the line from the stator to the rectifier (sized accordingly) It will protect the regulator should the battery demand more than the regulator is designed for. It will not become a PITA as it will reset itself. I have had a few Kohler engines (simple stator and about 9 amps charging coil but they have had rectifier/regulators, all blown (>$50 to replace) I installed the circuit breaker and so far so good. If it opens, it will reset, bump the battery a bit and reopen. Eventually, the battery demand will dimiinish to the point the breaker will not need to reset (or worse case, fail but it is cheap and can be wired so it plugs in). In the meantime, you have circuit protection for shorted rectifier, wires, bad battery, etc.


Cheers,

 

[halfor]

Re: New guy with charging voltage question

I am now wondering?.I have a trolling motor that has a second trolling only battery I have not used this motor yet because the hole boat is new to us and getting used to everything that goes along with boats, I haven?t been able to just go out and fish or just putt around. Anyway?. Would it be a good idea to connect both batteries together so they both would get recharged when running? Seem like I should be able to use the extra running voltage for somthing??

 

[j_martin]

Re: New guy with charging voltage question

I am now wondering?.I have a trolling motor that has a second trolling only battery I have not used this motor yet because the hole boat is new to us and getting used to everything that goes along with boats, I haven?t been able to just go out and fish or just putt around. Anyway?. Would it be a good idea to connect both batteries together so they both would get recharged when running? Seem like I should be able to use the extra running voltage for somthing??

I'm assuming the cranking battery is a group 24 marine starting battery. If after partial discharge, it goes right up to over 16V when engine is run, it has a problem. If in doubt it wouldn't hurt to pull it and take it over to Wal-Mart's auto service center and have them test it. A normal battery will go higher in voltage is charged from a current source as they age. Of course if the electrolyte is allowed to go below plate tops, it'll both go over voltage and be damaged permanently. Your system is a 9 amp current source, where the load (battery) determines the voltage delivered. The stator is current limited by design, and unless you also grossly overheat your engine, you're not likely to hurt it with an overload like the lawn mower setups will. The circuit breaker in the stator circuit idea is not for this engine.

You can hook up batteries in parallel if they are similar in design and approximately equal in condition. (age) If they are not ballanced one will take a charge, and the other will be damaged over time by undercharging and become sulfated. Also remember that when you're out of electricity, it's all gone. With 2 separate batteries you always have the swap out or jump options available for an emergency start.

Another advantage of parallel batteries is that you usually have a partially discharged battery bank that will hold down the voltage, usually to about 14 V.

I don't know what ignition is on your engine, but if it's switchboxes like the v6's, they can't be hurt by battery over voltage.

hope it helps
John

 

[Shawnee]

Re: New guy with charging voltage question

I stand corrected. I am a fan of circuit protection. Go with the advice of those that have way more experience in the marine field than me.

j_martin, out of curiosity, how is stator current limited?

 

[j_martin]

Re: New guy with charging voltage question

I stand corrected. I am a fan of circuit protection. Go with the advice of those that have way more experience in the marine field than me.

j_martin, out of curiosity, how is stator current limited?

The Iron core saturates, limiting the number of flux lines that can intersect the coil.

A well designed alternator will have coils that can operate continuously at the maximum current the core flux will generate. A poorly designed one will have too small a wire, thus overheating and burning out.

The old mercury stators burning out was basically a function of very poor insulation that couldn't take ordinary amounts of heat.

There's other considerations too, including the magnetic hysteresis of the iron, mechanical lamination limiting eddy currents, etc.

 

[Dewi]

Re: New guy with charging voltage question

I have a J30RLCOA 1985 and have just converted it to an electric start - starts immediately and runs OK - now I need to add a charging circuit - there are three wires coming from the stator and I have not yet put a meter on them when she is running - I have a bridge rectifier capable of carrying the current - now when using these previously I have just connected the two AC wires to the bridge and taken the pos & neg from this - what the third wire is for I do not have a clue - can one of you enlighten me as to what I actually need to do to charge the battery - looking on ebay the rectifiers for Johnson's all appear to have 4, 5, and even 7 wires coming from them - do I need to purchase one of these or will my two AC input and + & - output bridge do?? -

 

[mr 88]

Re: New guy with charging voltage question

Dewi start a new thread in the johnson evinrude forum.

 

[Dewi]

Re: New guy with charging voltage question

OK will do