Battery Overcharging

[Biggles]

Hi,<br /><br />I have a problem which initially I have tried to solve by reading previous posts on this forum.<br /><br />I have a 50 HP 2 Stroke 4 Cylinder Mercury Blue Band circa 1984.<br /><br />The engine is charging at 16.4 volts but will drop down to 15.9 volts if I turn on a spotlight.<br /><br />From my research I have realised that <br /><br />a) The charging circuit does not have a regulator<br /><br />and <br /><br />b) This is quite common.<br /><br />From the varied posts I'm not too sure if its a good or bad thing. But my Navman Radio doesn't like the high voltage, the GPS and Depth gauge don't seem too bothered. My brother who is a vehicle electrician says its bad. What do you guys think ?<br /><br />Because I don't want to fry my electrics or the battery or me has anyone found a way to fit a regulator into the circuit.<br /><br />Is it possible to fit one from a car or motor bike ?

 

[Laddies]

Re: Battery Overcharging

Get a battery with more capacity or try a battery wired in parallel with the battery in the boat

 

[Biggles]

Re: Battery Overcharging

Right laddiesservice different battery it is then.<br /><br />Many Thanks.

 

[Biggles]

Re: Battery Overcharging

Okay,<br /><br />Problem not solved.<br /><br />I,ve tried a different battery and I've started to replace the wiring which is in an awful state. <br /><br />Because of the lack of a regulator on this engine and because it puts out 16.4 Volts from the alternator, where is the safety valve as such to bleed of the extra volts. The average battery should only recieve 14.5 volts. If 16.4 volts is coming straight from the alternator where is the extra 2 volts lost. The wiring goes straight from the solenoid to the battery and doesn't seem to have any way to loose the extra voltage as such.<br /><br />A friend of mine is convinced that the wiring is at fault. It has AC 15 Amp wire at present and he is going to replace it with DC Automotive wire. He is convinced that will create some resistance and loose the excess voltage. Is he correct or is there some other way of correcting this overcharge. <br /><br />I thought I would pose this question now as I have a week away from the boat and the time to get some technical assistance before we start again.<br /><br />All the crappy wire to the electrical ancilleries have been replaced and all connections to the battery and the main ground have been renewed and checked. Do we now just need to do the wires between engine and battery ?<br /><br />I can bring the voltage down to 14.5 volts by running my Nav Lights and a spotlight continuosly. But without this the voltage climbs rapidly to 16.4 volts. Obviuously I am reluctant to continue running at 16.4 volts.<br /><br />Any help would be appreciated.<br /><br />Regards Biggles.

 

[chuckz]

Re: Battery Overcharging

AC and DC wire? I don't think so.<br /><br />The wiring between the engine and the battery is the most critical in keeping the output voltage down. If the resistance between the battery and engine is increased, the charging voltage increases! Ohms law: volts = amps X resistance.<br /><br />The "ancilleries" wiring should get it's power from the battery end of the wiring not the engine side. I bet if you check the voltage at the battery it never goes to 16.4 volts. The battery helps regulate the output voltage. That is why you never run an outboard without the battery connected.

 

[Biggles]

Re: Battery Overcharging

Hi L.I Chuck,<br /><br />How do we seperate the wiring so that the ancilleries get their power from the battery and not the engine side ?<br /><br />At present each pole of the battery has 3 wires connected to it. One of each will be from the charging system.<br /><br />Regards Biggles.<br /><br /><br />I am not too sure where the others go at this time, I'm not with the boat but I bet one set will go to the ancilleries and the other set is for the control box etc.<br /><br />As I said all these wires are connected directly to the poles of the battery so I should imagine that once the battery is charged the excess charge can then go to the instruments, as the battery is full and doesn't want anymore power.<br /><br />Whats the key to seperating the engine side from the instrument/ancillery side please.<br /><br />How do I wire it so I can make sure that the battery is acting a regulator ?

 

[Silvertip]

Re: Battery Overcharging

If your friend thinks there is a difference between AC and DC wiring, he's mistaken. Solid conductor and stranded, marine grade, yes. If you have any friends that are electronics engineers, they would certainly have the expertise to build a simple regulator for using a zener diode. Zeners have the ability to pass current until a certail threshold is reached at which time the excess voltage is shunted to ground. Otherwise, do some research and see if a regulator from a larger motor will work.

 

[Biggles]

Re: Battery Overcharging

I've still been working on sorting this out and have scoured the internet for information. Many people seem to have the same problem.<br /><br />My information points towards the battery being the culprit in many cases.<br /><br />Exactly what type of battery should be fitted to this system? <br /><br />various people extol the virtues of Leisure, Deep cycle batteries and even normal automobile batteries but can anyone recomend a battery that they have used after having a similar problem as mine.

 

[chuckz]

Re: Battery Overcharging

If the battery connections are clean and tight, the voltage shouldn't rise above 15 volts. Disassemble the connections, clean and degrease them.<br /><br />There is no such thing as "excess voltage". Current is supplied to the battery, as the battery charges the voltage rises. An outboard charging system is not able to supply enough current to drive the voltage up to 16 volts unless there is a poor connection.<br /><br />You're right, many people have this problem but most don't. The system is designed for the battery to regulate the voltage. It works if the connections are clean, tight and grease free.<br /><br />This is a maintenance problem and not a design issue. There is no need to design a regulator into the circuit. You could use a zenor diode circuit but a three pin voltage regulator would work much better IF you want to redesign the circuit.

 

[jtexas]

Re: Battery Overcharging

biggles, 3 wires to each pole of the battery; one of each is a big 'ol cable leading to the engine, right? Those same cables conduct electricity from the battery for the starter motor and from the charging system to the battery when the engine is running. That's all you need to run your motor. <br /><br />One of the other two sets is probably the tilt/trim, and the other must be to auxiliary fuse box/ground bus. If you don't have electric tilt, then the other two are both accessories. That's correct, no problem. Although if yours is like mine was when I got it, you may have miles of wire in there leading to nothing, where previous owners have added or replaced accessories, put in new wiring without taking out the old.<br /><br />What kind of battery? Not automotive. Marine batteries are built tougher for use in harsher conditions; better container, better construction inside, so they'll be able to take a pounding. I use a dual purpose cranking/deep cycle Interstate RV/Marine battery for cranking and accessories, works great. Others will advise you don't need a deep cycle; I have no basis to dispute them. Either way, take care of it and it will take care of you.<br /><br />Here's an excellent resource for taking care of batteries.

 

[Silvertip]

Re: Battery Overcharging

Whether some batteries are better than others at handling higher charging system voltage is an unknown except to those that have had your experience and there are many. Probably many more have the problem but they just don't know it because their electronics hasn't told them. 16 volts is being measured so this is not a "not possible" scenario. Unregulated systems are just that -- unregulated for voltage and current, and the battery simply absorbs the current delivered to it. But that's not the issue here. The battery will likely live just fine at 16V since only at frequent, very long and runs will higher voltage create a problem. Its the electronics that doesn't like the higher voltage. The choice is to regulate it or run the electronics from a separate battery not hooked to the engine charging system. The accessory battery can then be switched into the charging system for recharge whenever the sensitive electronics are off.

 

[chuckz]

Re: Battery Overcharging

I did a little more research, if you have a fully charged battery and a charging system capable of greater than 15 amps, the voltage can rise that high.<br /><br />If you try to regulate the rectifier output you need a 16v X 15amp= 240 watt regulator. This can be done but is expensive. However, you can go to Radio Shack and buy 15 volt, 3 terminal regulators that can handle several amps as long as they are on a heat sink. They are very easy to wire DC IN, GROUND, DC OUT. They are cheap enough that you can use one for each piece of electronics you want to protect.

 

[Silvertip]

Re: Battery Overcharging

Amen L.I. He would only need one as the other electronics don't seem to mind the higher voltage.

 

[rdmcphe]

Re: Battery Overcharging

I have a 1980 Merc 50 with a rectifier based charging circuit. The unregulated supply was hard on my fishfinder and GPS. <br /><br />I solved the problem by creating a regulated circuit for my fishfinder and GPS. <br /><br />I used a MC7812 attached to heatsink. It works fine as is real cheap (The regulator chip was less than one dollar if I remember right)<br /><br />Here's a link to the datasheet...<br /><br /> http://www.datasheetcatalog.com/datasheets_pdf/M/C/7/8/MC7812.shtml <br /><br />You can also get something similar at Radioshack...<br /><br /> http://www.radioshack.com/product.a...name=CTLG_011_002_017_000&product_id=276-1771 <br /><br />The thing to realize with these low cost 1 chip regulators is that they require about 2 volts overvoltage to operate in regulated mode. This means that a MC7812 requires at least 13.5 to 14 volts to produce regulated 12V. With an unregulated outboard this this not a problem as long as it is running. <br /><br />It is a different issue entirely when the motor is not running. If there is insufficent voltage to provide a regulated 12V the 7812 operates in unregulated mode. It passes through the input voltage and skims off about 2 volts. This is spec'd as Vdrop in the datasheet. This means that when the motor is not running and the battery is fully charged the regulator will be producing about 10 - 10.5 V non-regulated. This may be an issue if the electroncs you are supplying require 12V. My fishfinder and GPS are OK with this.<br /><br />I hope this helps.<br /><br />Russell

 

[Biggles]

Re: Battery Overcharging

Thanks Guys,<br /><br />Thats a lot of info to take in now.<br /><br />What i'm going to do when I go down to the boat next week is replace the last of the old wiring. Double check the earthing points and then go through it with an ammeter checking the resistance as I go along. If that doesn't work then its on to rdmcphe' idea of the regulators.<br /><br />I'll keep you posted as to how I get on.

 

[Motor Boater Bill]

Re: Battery Overcharging

A couple things you might check with a voltmeter and the engine running (charging). Check the voltage across the poles of the battery without touching the cables, cable ends or wires. Then check the voltage across the cables. If it is different you have bad connections at the battery. Then you could check the voltage between each cable end and the battery post it is connected to, and this would tell you which connection has the voltage drop. My guess is that you won't get the full 16 volts just across the battery terminals. Let us know what you find out. Good luck!

 

[achris]

Re: Battery Overcharging

I think some of you are missing something very important. This is the reason why large capacity MARINE batteries are required when using one of these older, unregulated outboards. A marine battery is quite happy to soak up the 'over-voltage', a standard automotive battery just gets REAL hot. Worse case is they explode. <br /><br />The 16.4 volts you see is quite normal and indicates that the charging system is working correctly. You'll also find that most good quality marine equipment is rated for a wide range of voltage. My GPS is rated 12-24 volts and the sounder is 12-32 volts. I think my radio is happy up to about 18 volts. <br /><br />On the issue of using the battery leads to drop the voltage. BAD IDEA!!! any voltage dropped in cables is lost as heat. Heat melts cables, then you have a fire risk. Something you really DON'T want on a boat. (No way to run away from it). If you drop 3 volts through the battery leads at about 6 amps, that's 18 watts of power lost as heat in the cables. That's a lot of heat! It also means that the voltage to your electronics is 'dirty' or 'unclean'. Electronics really don't like that. Best thing is to use a 3 terminal regulator like rdmcphe suggests.<br /><br />Chris..............

 

[Silvertip]

Re: Battery Overcharging

Using an inexpensive regulator in the supply feed for a device is no more dangerous than a factory regulator placed on the engine. Those regulators fail for two reasons 1) heat and 2) reversed battery cables. The regulation method described here is perfectly safe if done properly. Neither the input wire or ground wire get hot if they are sized properly like any other wiring on the boat. The electronics don't operate on 12V either as the IC's inside them are very likely 5V devices so voltage is dropped again. It's really not a problem.