747guy Report post Posted June 27, 2016 I have had ongoing problems with my tach and speedo acting erratically. I have taken it to Allied in Coburg and they fixed it for 500 miles and told me it was a grounding problem. I have had other members indicate similar problems. Yesterday while returning from The FMCA rally in Albany, I ran the generator and the AC while travelling. Lo and behold the tach and the speedo worked perfectly. Yahoo....what a thrill to have a tach when running up and down mountains. So, I spent last night trying to draw a conclusion as to why the generator running fixed my problem. Transfer switch came to mind, but no other logical connections could I make. Any ideas Wolfe or Herman or anybody? Share this post Link to post Share on other sites
wolfe10 Report post Posted June 27, 2016 The tach and speedo are 12 VDC and work off the chassis battery. The ATS is strictly 120 VAC. It is the "selector" between shore power and generator so only a single source of 120 VAC can be used at one time. The only "overlap" between the generator/ATS and the tach and speedo is the inverter/charger. IF (yes IF) it senses voltage provided by the alternator is below the inveter/charger's bulk rate of charge, the inverter/charger will raise the voltage to the batteries. This raises a second issue-- as in many coaches, the inverter/charger ONLY charges the house bank. I do not know if yours is wired for the inverter/charger to also charge the chassis bank. Share this post Link to post Share on other sites
747guy Report post Posted June 28, 2016 Thank you for your prompt response Brett. I have had the house and chassis batteries recently replaced plus a new Xantrex 3000 watt inverter. My Monaco had a system that allowed both sets to be charged, but it was replaced with another unit. Your post points to the alternator not supplying high enough voltage to the chassis batteries, but while the generator was running, the inverter was supplying enough voltage to satisfy the needs of the tach and speedo. The voltmeter on the dash usually reads about 13 volts, so I was comfortable with that. what should I be reading from the alternator? 13.6 volts more or less? Share this post Link to post Share on other sites
wolfe10 Report post Posted June 28, 2016 Alternator reading at the chassis battery should be 13.5-14.2 VDC. Because the dash gauge is WAY "downstream" of the batteries, it may not be an accurate reading. A check with a digital voltmeter at the battery and then a quick look at the gauge should tell you how accurate the gauge is. That way, you can factor in a "fudge factor". Share this post Link to post Share on other sites
