View Full Version : strange voltage question

07-05-2005, 11:26 PM
I found this odd. I was driving my buddy's Toyota ski boat. It has a fully digital "trip computer" in dash. (I don't know how else to describe it) Anyway, it shows the volts to the tenth. At idle, it shows about 13.4....pretty good. At 35-40 mph, it drops to 10.9- 11.4. It seems the voltage should increase at higher rpms, not decrease.... Any ideas what would be causing that?

07-05-2005, 11:32 PM
i think the voltage regulators keep the volts from increasing with rpm, and as to the drop, maybe the higher rpm puts more load on the electrical system due to more spark being sent to the spark plugs :confused:

07-05-2005, 11:38 PM
I would think the regulator too, i think any engine does that.

07-06-2005, 02:56 AM
Maybe the voltmeter is being affected by vibration or the charging system is about to fail.. You won't get that kind of a voltage drop at speed if everything is working fine & reading accurately. A voltage regulator is exactly that - a device to keep the voltage around 13 - 14 v while the engine is running.

07-06-2005, 10:24 AM
At idle your voltage may be 12 +/-, at run speed, shouldn't you be seeing 14 + volts out of the alternator?

Maybe the fancy trip computer is just that - a fancy trip computer but not necessarily an accurate diagnostic tool?


07-06-2005, 10:39 AM
That doesn't make sense, hard to imagine how this could really be happening with a good battery. That would be a heavy load. Take a VOM and measure the voltage across the battery and compare with the dash. I suspect bad wiring at the computer.

07-06-2005, 11:39 AM
It's really weird..... It even starts flashing a warning, "low voltage"
Of course that's the least of his concerns. Crappy wake, poor handling and mediocre acceleration are things that can't be fixed! :D
Not a bad looking boat, though.....

07-06-2005, 11:51 AM
I looked at a Toyota seriously when I bought and was at the liquidation time and they had low prices, but glad I didn't as they are not the same.

07-06-2005, 12:15 PM
What should the voltmeter show when running a Mastercraft? Mine seems to stick at 12V even at speed, and I am not sure whether it always did this, or whether it used to show higher at speed. If it should show closer to 14V at speed, then maybe I have a battery or gauge problem???

Workin' 4 Toys
07-06-2005, 12:33 PM
Should stay a pretty consistant 13.5 idle and of any speed. And 11.5 to 12 with the engine off.