It started fine and THEN said 9.9 after the engine was running or was it saying 9.9 whilst starting (the pop up warning may have a time delay so not be helpful). If you had one engine running even for a few seconds and the voltage was reading 9.9V then that doesn't sound as simple as the battery - perhaps the alternator? perhaps the wiring? because the alternator should be putting out >12.8V. Do you have an alternative way to check the voltage at the battery - in a past life I had plotters which read quite different from the battery themselves due to corrosion on the wiring/master switch and was particularly sensitive to engine starts?
2 batteries is so you have options if one dies! is it two starting batteries one wired to each engine? or a starting battery (wired to both engines) and a house battery (for your lights etc) which can also be linked to the starter if that fails?
Not sure but as it is on the plotter I assume NMEA.
Charging alarm goes off as soon as both engine start. Is it feasible that the voltage would drop to 9.9 for a millisecond after a start, and this notification was slightly behind the curve I usually start up the engines, then boot up the plotter and any other electrics I want on.
LOL, not saying you're wrong, but I would assume the opposite!
Actually I think you are both saying the same thing - its most likely to be measuring the voltage on the NMEA/SeatalkNG network rather than having a dedicated sensors sending the data to the plotter via that network. If he had networked voltage sensors I'd expect them on each battery and separately displayed?
Its definitely possible that the voltage drops at the moment you turn the key (when the starter motor is working). You'll probably have noticed something like this in a car at some point - when starting the headlights and possibly dashboard dim. It shouldn't go below about 10V when cranking - but if your network wiring is long and has a 0.2V loss, that MIGHT account for it. Personally my instruments are fed from the house battery not the engine battery. BUT you definitely want to understand how its all wired because if a battery is on its way our you want to be able to switch those 1/2/Both options to get you home.
It's nothing to do with the network, what if there isn't a network ? The voltage show is from the power input to the plotter.
It isn't a possibility, it's a certainty. The initial current inrush will be high, the the voltage drop will reduce as the engine starts to turn over.
Again, networking is irrelevant.
Agreed.
Which is a Raymarine plotter so is it not powered from the SeatalkNG network, even if that’s the only item on the network?
For a man who was banging on about nitpicking the other day you’ve done nothing to help the OP - the question that matters is whether 9.9v is an acceptable level of voltage drop during cranking.
Most people seem to say <10V is a problem. The point someone else was making about network (which you are right could just as easily be an independent power supply) is that if the voltage is being measured at the plotter it’s probably a bit less than at the battery anyway. IF (and it is unlikely but not impossible as the OP doesn’t know what he has) the voltages are actually measured direct at the battery and that data fed to the plotter digitally rather than being subject to the voltage drop in the wires to the plotter it would be more alarming than if its 9.9v at the end of a long thin cable. The OP has indicated that he doesn’t know if this is new or it’s always done this as he normally turns instruments on after engines.
I doubt it.
No, it is absolutely NOT powered by the STNG network. The network could not support the current required.
Post #11 is to help the OP. Your misinformation not only doesn't help, it hinders. A reading of 9.9v, briefly, at the plotter doesn't really tell us much. The plotter is wired with small wires and isn't know to give accurate voltage readings. Current inrush at initial start and an inaccuracy at the plotter could mean that a reading 9.9v is acceptable. What we might need to know is the actual voltage at the battery.
That's just more guess work, which is incorrect and misleading. I have already explained that the plotter has it's own power supply and the voltage reading is taken internally from the plotter
I doubt that many people do know, or even care, as long as everything works as they expect it to.
You are correct, it has it's own power supply, as does every plotter i've ever seen.
Correct again, "battery voltage" as far as the plotter (and almost every other instrument) is concerned is its internal voltage. It's rarely accurate in my experience.
N2K PGN 127489 can give battery voltage. But its part engine data, so the plotter still won't show that as part of it's own voltage reading. It would need engine data on the network and a separate page set up on the plotter.
| 127489: Dynamic engine parameters |
Sounds like one cell is duff, you seem to have lost 1/4 voltage. Quite common issue with batteries.
I am fairly sure that the manual for my B&G plotter advises exactly that.