What to do if electrical load exceeds charging system capacity?

[Boatleech]

I'm replacing a fried Mercury rectifier/regulator p/n 815279-3 with a CDI 194-5279. (1994 40HP Mercury, s/n 0G084586, red stator.) As part of the battery charging system check, my Clymer manual says to determine if the accessory load on the battery is greater than the charging system's capacity, and if it is, reduce the load. Well, it is -- probably a lot greater than the 9A this stator will supply. But the boat's owners like to go fishing at night and have some pretty serious lights on board.

Will overloading the regulator burn it out? Seems like a sorry design if it will, but in any event I'm looking for a solution that will allow these folks to go fishing but not burn out their rectifier/regulator. Are we looking at a two-battery system here? Would appreciate suggestions for how to do that at reasonable cost, but I don't see a way offhand without using an external charging system of some kind. Unfortunately, shore power isn't available where the boat is moored.

 

[thefairlaneman]

Re: What to do if electrical load exceeds charging system capacity?

I would use another battery and put a quick charge on it at home before you go out. If you are using alot of extra stuff that uses batt power this should solve it. If not there is something wrong in the engine charging system. Make sure if you have an auto belge pump its not running all the time for this will drain your power too.

 

[Sig_Mech]

Re: What to do if electrical load exceeds charging system capacity?

Boatleech, something else that might help with the amperage draw is to switch all your lights over to LED's. This might be a little spendy but if you look around you can find 12V LED's for a reasonable price. They also give you the added advantage of lasting longer and burning brighter while drawing minimal amps.

 

[Silvertip]

Re: What to do if electrical load exceeds charging system capacity?

A nine amp alternator is not a sorry design. You can't continue to overload to ANY charging system and expect it to keep up. Adding another very large capacity deep cycle battery adds capacity but it does not solve the charging issue. Even if you had a 20 amp charging system I doubt that system would keep the batteries charged since it takes a very long run at wide open throttle to accomplish that. Your only choices are to add battery capacity or reduce the load by using fewer or more efficient lights. Add an on-board charger that you plug in at the dock to keep the batteries charged.

 

[Boatleech]

Re: What to do if electrical load exceeds charging system capacity?

The 9A system is a sorry design only in that it apparently doesn't self-protect itself from excess current demand -- not a difficult thing to do.

I like the LED lights idea, but the owner is getting burned out from repairing her bargain boat, and wouldn't be terribly receptive to spending big bucks. I think I can talk her into installing a simple switch system as recommended at http://forums.iboats.com/showthread.php?p=1682352, and let her worry about how to charge the deep-cycle house battery from shore power.

 

[j_martin]

Re: What to do if electrical load exceeds charging system capacity?

The Mercury bridge rectifier is really an older can type rectifier that isn't even available any more. (the press in can itself) If it is replaced by a BR-25 packaged (25 amp bridge rectifier, .250 tab terminals) rectifier failure is history.

Get one at mouser.com, Digi-key. should be at least 200v PIV rating. Rad shack's 50 volt version is said to work, but it is actually underrated for the application.

The stator itself should be protected from overcurrent by it's design.

hope it helps
John

 

[Boatleech]

Re: What to do if electrical load exceeds charging system capacity?

Thanks, John; this motor uses a rectifier/regulator, not just a rectifier, otherwise the component bridge rectifier route would look very attractive. If I could find some design data for a lead-acid charging regulator, I'd be tempted to try to come up with a replacement rectifier/regulator, but that's a project for another day. I think everything you need to know is at http://www.batteryfaq.org/ and http://www.landiss.com/battery.htm, but it's a long leap from data to a working gadget.

For now we're going with the CDI replacement rectifier/regulator. Wish someone would talk iboats into using USPS priority mail...

 

[j_martin]

Re: What to do if electrical load exceeds charging system capacity?

I think the rect/reg unit is a series regulator, taking a lot of punishment at high currents, and having to dissipate a lot of heat. If there's a way you can improve the heat dissipation, it'll live longer.

hope it helps
John

 

[Boatleech]

Re: What to do if electrical load exceeds charging system capacity?

About all I can think of offhand is thermal conduction paste between the heat sink of the R/R case and the (water-cooled) engine block it mounts on. Probably wouldn't hurt, anyway.

 

[achris]

Re: What to do if electrical load exceeds charging system capacity?

Unless there is something else wrong, drawing more current than the regulator can provide will not cause any damage... just drain the battery.

A charging system that can't 'protect itself' is indeed a sorry design. Merc's charging system it not one of these.

Chris...........

 

[j_martin]

Re: What to do if electrical load exceeds charging system capacity?

About all I can think of offhand is thermal conduction paste between the heat sink of the R/R case and the (water-cooled) engine block it mounts on. Probably wouldn't hurt, anyway.

The heat sink compound is required. They will routinely smoke without it.

been there, done that.

hope it helps
John

 

[Boatleech]

Re: What to do if electrical load exceeds charging system capacity?

Hmmm. There sure wasn't any there under the old (smoked) one. It lasted for 14 years, if the date code is to be believed. I didn't know about the requirement, though -- may be in the CDI instructions -- but I was going to hunt up my lifetime-supply tube of Arctic Silver anyway. Thanks for the heads-up.

Mike