Stereo voltage issue

What voltage is everyonoe seeing with there radios on? My boat runs around 12.0-12.5 when the baot is running, and 11.3.11.8 when the baot is off. Is there a way to test the altenator to see if it is pushing enough amps and volts? I have two amps pushing about 1000 watts rms total. I see stock boats exactly like mine w/ no stereo running in the 13.2-14 when the engine is running.

A fully charged battery, at rest (no current going in or out) should be right around 12.5 volts.

Any voltage less than that, with the engine running, is a sure sign that the alternator is not putting out enough. At 12.0 volts the alternator is not keeping up and the battery is actually discharging.

Where are you measuring the voltage, and how? You should use a reasonable digital multi-meter and measure directly at the battery. If you measure at the fuse block or at the amps you can be getting a false reading due to the voltage drop in the wire.

The best thing is to have the engine running at least 2000 RPM and measure directly across the battery terminals. If you aren't getting 13.2 volts or more then I would highly recommend getting a new alternator or turning the stereo down.

adam did you check it with a multi meter? or are goin off the guage?

tht's just off the guage on the amp, but my guage in the dash reads about the same. I need to get it in the water and test off the battery. My PP voltage meter also reads low. I will test off a multimeter this weekend.

How are the amps connected to power?

If the amps are making their +12 and/or ground connection at the panel/fuse block then I am not surprised that your voltage readings are low. I am a little surpised that you aren't popping the main breaker on the engine, however.

My suggestion is to run a separate power and ground connection from the amps directly to the battery. Install a fuse in the + lead as close as possible to the battery. This will keep the current that the amps need from dragging downt he voltage to the rest of the boat.

Right now the amps are run directly from the battery,stinger isolater/relay( no main fuse, only fuses in the amps themselves) to a capacitor, then to the amps. I was going ot install an 80-amp fuse in the main 4ga coming off the positive of the battery. I am also going to test at various points to determine where the voltage loss is occuring. Stinger claims no voltage loss across their relays. I have not tested the relay

In the two examples you gave, both show that you are dropping .7 vdc That is what a diode isolator will do. Measure the voltage drop across the isolator. if it uses a relay, the contacts should show no drop at all.

And, your alternator is not putting out. A new one isn't that expensive.

I may be wrong, but arent you supposed to show 14.4 vdc when running, not 12?

stinger isolator/relays are not supposed to have the .7 voltage drop. that is why I went with them. And yes in a car you should show 14.4, but I have yet to own a boat that gets that high. If the altenator wasn't putting out wouldn't the batteries eventually drain down after a day of listening to the radio/ running around all day? Maybe the altenator isn't putting out enough amps? I wouldn't think w/ the setup I'm running now would require a bigger altenator. I've run more wattage in my truck

Adam:

Something to consider:

The primary purpose of a fuse/circuit breaker is to protect the wiring and safegaurd against fire. If a short develops, the massive current flowing through the wire will turn it into a heating element. A 4 ga heating element could easily do a lot of damage.

The longer the run of unprotected wire, the greater the risk. Some things you just can't fuse, such as the starter motor, but most other things you can.

Capacitors, especially the very large ones, are notorious for developing internal shorts. It scares me to have 4 ga wire connecting the battery to a large cap without a fuse.


You described the + side of the circuit well, how about the negative side? Where does everything tie together? You should be running at least a 4 ga wire from the negative of the amp to the capacitor and then on either the battery directly or to a large bolt on the engine block. If you conected negative to some common point up under the dash or similar it could cause all sorts of problems.

I'm running 4ga from the (-) battery to the (-) of the 1.5 farad cap. From there i'm running 8ga to the two amps. I'm going ot put the fuse on the (+) today, and then start checking voltages at various points. The people @ stinger told me I could see a small voltage drop across tere relay, like .1-.2v. but not likley.

here is the real fact we all use standard marine alts. and the dont put out enough juce for what we all run off them. i.e. high power stero, amps. and lights. when you do this to a car or truck its recomened that you upgrade your alt. i have looked into it and can't find one. does anyone have any idea where to look

do a search on battery shack, they'll rebuild or custom make an alt. I would also think you could go to any altenator shop in your city and have one built. make sure they put some sort of spark arrestor on it. they could take the ones off your current one.

adam...I used to have a stinger isolator/relay and had the same low voltage issues. My system is around 2500 watts. I upgraded my alternator from 65 amp to a 150amp and still got only ~12volts. Recently I took the stinger relay off and replaced it with a perko switch. My voltage is now ~14volts. I think there is a significant voltage drop when using the relay.

I hope that is not my problem. According to stinger there relay's have 0-.1 voltage drops. I couldn't find my multimeter this weekend and didn't check to find where the drop is, but I think it may be the altenator, b/c w/ the motor turned off I was seeing 12.1-12.3 volts.( off the amp voltage meter) If there where a larger voltage drop I would see it reflected on the amp's volt meter. I like the fact of not having to remember to turn a switch every time I start/stop the boat.