Need advice on alternator problem

[o1how]

Hello
I have a 27 ft Rinker witch I just bought this spring. Boat is equipped with all nornal electronics,and duel bratteres. When running the boat with the battery switch on #1 & no electronics on, the alternator gage will show middle of gage 13+ When I turn on the fridge, radio, & a small 12 volt cooler the gage drops well below middle, and if I go to use the trim the gage will fall well into the discharge. After a day on the lake of boating & drifting, the #1 battery is very weak.
I throught the alternator might be poor so I took it off & had it tested, it tested ok. The alternator is only a 65 amp, I was thinking of getting a
100 amp or a 140 amp. Witch one should I go with? is there such a thing as going to big? or do I have another problem i'am not a where of?
Thanks
How

 

[Splat]

Re: Need advice on alternator problem

Bigger is always better. The batteries will only take the voltage they need. Thus a bigger alternator will only supply the current that the system requires at the moment.

The cooler and the fridge are big consumers of energy. However I would think that a 65 amp alternator should keep up with them ok, but you have to remember the alternator only works when the engine is running, and running above idle. How long are you running the engine compared to total time the accessories are running?

I can't remember but I recall hearing that a 12v fridge can draw almost 20a when it's running. Can anybody substantiate that one? I know my thermal electric cooler draws almost 5 on it's own.

Bill

 

[tashasdaddy]

Re: Need advice on alternator problem

i think the fridge is 20 amps on start up, when the compressor kicks in.

 

[Silvertip]

Re: Need advice on alternator problem

Remember that if all of the high-current draw accessories are running when you are drifting, juice is leaving the battery at a very high rate. Lets use an arbitrary number of 25 amps. If you did that for one hour, you would have to run the engine at a speed that allows the alternator to output its 65 amp maximum and you would need to run that way for nearly 1/2 hour to put back that amount of juice. If I were running the stuff you are, that boat would have the largest alternator my budget could handle. You can't go too big, just too small.

 

[waterone1@aol.com]

Re: Need advice on alternator problem

Get the largest alternator you can that will fit the belts and pulleys. The other item you need to look at is the wiring condition and the ground connections. Even with a 65 amp alt., you should not be killing your batt durring normal operation.

 

[o1how]

Re: Need advice on alternator problem

Thanks for the reply Bill
On a normal day of 8 to 10 hr I would run the engine about 50% of the time, and when the engine is running it would be about 1800 to3200 RPM.
When at cruseing speed and the battery is fully charged, and accessiories are on, the amp gage will show in the +, but at the end of the day and the battery is weak and at cruseing speed, accessiories are still on, the gage will show in the -. If I turn off the accessiories then the gage will show in the +.
This is why I think the alternator is too small.

 

[Silvertip]

Re: Need advice on alternator problem

Just because the gauge is showing positive charge does not mean the battery is charged -- it simply means more juice is going to the battery than to the loads --- in other words you are not losing ground so to speak. If you have a 25 amp load when running, about half of the available maximum alternator output is going to the battery and the other half is needed to run the engine and the other loads. Charging isn't about "instant" readings on the voltmeter or amp gauge. Time is a factor as well.

 

[o1how]

Re: Need advice on alternator problem

Thanks for the reply
When I took the alternator off the main power wire has a thread together link
I guess it like a fuseabull link, but when I unthreaded it there is no fuse, nothing in there. I guess it is just a thread together wire. Is this something that could cause my problem? All other connections look fine. This is a three wire alternator, if this a difference.

 

[Splat]

Re: Need advice on alternator problem

He's talking about the gauge reading around thirteen in the beginning of his first post. I believe he has a volt meter he is looking at, not a amp meter.

Do you know how old the batteries are? As batteries become older their reserve capacity drops, and they take longer to recieve a full charge. I'm wondering if this is not contributing to your problem?


Bill

 

[Boatist]

Re: Need advice on alternator problem

It is not clear if you have a VOLT Meter or a AMP Meter. To be sure of what you are saying it would help to know which you have.

Your alternator may be big enough and good but your wireing may be too small. I seen many 60 amp alternator that under the type load you are putting on it the belt slips. Sometimes it will make noise but often it makes no noise but is slipping so it can not reach full current output.

Also I have seen a lot of 60 amp alternators that use 10 guage wire on the alternator output. 10 Guage is good for about 30 amps and above 30 amps are going to see a lot of voltage drop. So with all the load turned on and the motor running above 1500 Rpms check the voltage at the battery terminals. If your reading around 14.4 volts or above the alternator is not the problem.
If the voltage is below 13.8 volts then check you voltage at the alternator output. If it much higher then you need larger wire from the alternator to the battery or battery switch.

Another important factor is the size of your battery. Your alternator has a voltage regulator. The voltage regulator Job is to control the output voltage of your alternator. They will usually regulate the voltage somewhere between 13.8 volts and 15 volts. The average output on many is 14.4 volts but each is different. To find out what your voltage regulator is set at turn off all the load and start the engine an run at 1500 rpms or above. Put a volt metter on the battery terminals. After Starting and if the battery had a normal charge before starting then you should see the volt meter move from 12 volts up to the voltage of your regulator. The voltage will clime until it reaches the voltage of the regulator and will not clime any higher.
If the alternator and the wireing are big enough then when you switch the load on the voltage will stay close to this same voltage. If it starts dropping then the alternator or wireing are not big enough. Now the alternator will put out more amps at a higher RPMS but if it requires higher then you will have to run at higher RPM to matain your charge. At least in my case I would not want to have to run at higher RPMS just to maintain my charge under load.

Now if you discharge your battery by running the iteams without the motor running the battery will discharge and supply the load. When you start your engine the alternator should supply your load and enough voltage to recharge the battery. The Regulator will set the max voltage an as long as the battery terminals have that voltage it is up to the battery to accept the charge. At first it should take a lot of amps but as it charges will accept less and less curent. To reach full charge will take several hours even with a 140 amp alternator.

One last thing I would check and do this safely. With the motor running turn the load on ane run at 1500 rpms. After running for some time check the temperature of the alternator case. Next check the temperature of the output wire. Check the wire near both ends. If the wire is getting hot go to a bigger wire. Also if the alternator is getting very hot then you probably need a larger alternator that will run cooler at the same amperage.

 

[o1how]

Re: Need advice on alternator problem

I believe it is a volt meater, the one in the dash. The batteries were both new this spring when I bought the boat. I don't know how big the batteries are, the boat is in storage & to far away to go and check, but I know they are both marine batteries. I did check the alternator to see how hot it was getting after running for a few hours, it was hot, I could not hold my hand on it. Does enyone know what that thread together wire is going to the main power terminal on the back of the alternator?
__________
I too enjoy the Great Outdoors.
In the hart of Rocky Mountains, Shuswap Lake, British Columbia, Canada.

 

[bruceb58]

Re: Need advice on alternator problem

The problem with the gauge at the dash is that it is measuring the voltage after many voltage drops. All the loads are after the alternator and battery and before the gauge. I would at least do a test with a multimeter at all points to determine what your voltage drops are. Your alternator may be fine and it is just losses in undersized wire and bad connections that are your real problems. when you do your voltage drop measurements, use one common ground for all of your measurements, preferably at the battery. You will need a long test lead for your ground in order to make these measurements.

 

[Silvertip]

Re: Need advice on alternator problem

A fuseable link is not a fuse but a piece of wire that is designed to melt at a specific current. It is spliced into the power wire and usually has a clear splice protector on the joint. If that's not connected your battery(ies) will not charge.