confused/perko thread

I just had a perko switch and 2nd battery installed, so let me see if I got this right. #1 battery is my primary which is what the dealership told me, so I stop in a cove and play the stereo for 2 hrs and leave it on #1 and only go to #2 if the boat wont start then go to both. Or...pull in the cove shut down to kick it for a couple of hrs and switch to #2 play my stereo then when I leave switch it to both for about 30 minutes of running time and then stop shut down and place it back to #1 and I'm all charged and good?

I am interested in getting rid of my relay and going with a Perko switch . Where did you install the switch ?

cope and mcpheters in santa clara installed it for me

Rob:

In principle, either of the methods will work, depending on just how much current your stereo draws and how faithful you are about operating the switch.

Niether of those are sure bets.....

Most wakeboard boats I have seen that run tower speakers and subwoofers are capable of pulling 100 amps from the batteries. If you anchor in the cove and run the stereo loud enough to be blasting you while you are up on shore you will be pulling a lot out of the batteries. In a couple of hours you may have drained the batteries a fair amount, and then if you continue to run the stereo as you cruise around 30 minutes will not be nearly enough time to recharge.

How big is your alternator?

I have the stock 65 amp alternator on my boat. I run 4 tower speakers and a sub. The total power of the amps is 600 watts. Peak current to the amps is around 50 amps but I would guess the average is more like 25 when I am cruising.

If I am running the stereo, bilge blower and ballast pumps the alternator does NOT keep up! And this is at wakeboard speeds, ~2800 RPM. In this condition, it is possible to drain the batteries even though the engine is running!

When I shut the pumps and/or bilge blower off the alternator will keep up, but it doesn't have much margin. I would guess that I have less than 10 amps left over for charging the battery. At this rate, it would take 5 hours of cruising to replace what I might use in two hours of sitting.

Tell us more about your setup and I can comment some more on it. Do you have amps? How big? How many? How are they connected to the battery?

Any other large power draws? Tower lights? Ballast pumps? Heater?

How big is your alternator?

My standard answer to these types of questions is to get a "Battery Combiner" and connect it between the two batteries. Leave the battery switch on just one battery. If both batteries are the same type you might want to alternate which battery you use just so you can tell if one is starting to go bad. The battery switch will allow you to switch in the alternate battery to get you started if you run the primary down, and the battery combiner will always keep the alternate battery charged up and frees you from having to remember to do anything (it is all automatic)

Rod, are you using ohm's law to calculate your current draw from yoru amps? if no,t how do you arrive at your figures? Another question, will two identical amps totaling 600 watts RMS draw more current than one amp (same brnad, but bigger) totalling 600 watts RMS?

Rod--
Is a 65 amp alt pretty much typical for wakeboard boats from the factory ?

JTW, I believe so. Mine was rated at 65, but was tested out in the high 70's. (04 22 SSV)

(Message edited by acurtis_ttu on November 03, 2005)

PCM 100 amp standard, Indmar 90 amp

I just got home and pulled the cover off my Sanger . It has a 70 amp alt.

Alternator size: I haven't measure the output or even inspect the alternator to see what it might say. The specification for the boat (Super Air Nautique) when I bought it said 65 amps so that is the assumption I have been making.

Adam: Ohms law is uselss in this situation. Current draw is something that is really hard to measure. Unless you are playing a constant, steady tone the power draw from the amp is wandering all over the place.

As far as one large vs two small: depends. The "economy of scale" dictates that it is more efficient to make one large system rather than two small systems. However, it would be possible that two well designed amps could be more efficient than one poorly designed amp.

The max "peak" current I estimate based on the peak power capabilities of the amp and figuring a 15% power loss in conversion. The average power draw I estimate based on how long it takes to drain the 100 amp-hour battery (which I assume is actualy going to provide 85 amp-hours at the draw the amps will pull).

The excess capacity (or lack thereof) of the alternator is much easier to come up with: With everything running, the warning system on the dash starts beeping at me, and the volt meter has dropped to 11 volts or lower.

Rod where did you ge the 15% power loss, my understanding was that most amps are only around %60 efficient. Your saying %85 efficient??