Hi, haven’t found a direct answer - I’d like to connect my fuel tank senders to my CerboGX and by extension my NMEA2000 network. What I’d like to know is if I can connect wires from the sender to the Cerbo tank input, while the senders are already connected to the analogue fuel gauges. In essence a parallel connection. The senders are basic 33-240 ohm resistive. Thx.
Tank senders like the ones you have are actually variable resistors. And gauges are actually voltmeters.
The tank senders are connected in series with the positive terminal of the power supply/battery and thus power the gauge. When the tank level changes, the resistance of the tank senders changes, and with it, the gauge reading.
The Cerbo GX tank inputs require the pure resistance of the tank senders. Therefore, no voltage should be applied to them, as this will damage the tank input of the Cerbo GX.
I am not familiar with NMEA2000 matters, but I just saw a quick Google search that there are ways to connect a Cerbo GX to NMEA2000. So perhaps you can connect the tank senders directly to the Cerbo GX and also establish a connection from the Cerbo GX to the NMEA2000 so that the information becomes visible there as well.
Thank-you for the prompt reply Theo, it helps a lot. A couple more details:
Background: this config is referring to my fuel tank gauges only. There are 2 fuel tanks, but only 1 gauge. The way it currently works, is you turn the ignition key to the first “on” position, and switch a DPDT momentary ON-OFF-ON switch to one position or the other. That will then show the relevant tank level info on the gauge. Therefore, the wiring to the sender(s) is not energized all the time; only when this rocker switch is operated. This is ok most of the time but not as good as individual gauges.
I already have the Cerbo connected to my NMEA2000 network, so that’s working…but just ok. Not great because the Cerbo display on the Axiom MFDs is not very flexible or user friendly, but basic function is there. Currently, my fuel tank info gets fed into the N2K network by an analogue to N2K converter made by ActiSense. It is not a great setup which is part of the reason I asked the original question. The biggest problem is the only tank level info that gets to the N2K network happens when you manually trigger the senders via the rocker switch. Ergo no continuous readout, and only one tank at a time.
One last detail, I am going to replace the fuel tank sending units. Existing ones are old and inaccurate. What I replace them with is governed by the requirements of integrating it into my system.
Having said all that, number one choice would be a simple manual sender unit (by KUS if it makes any difference) connected to both the existing analogue display and also the Cerbo. Next best would be the same but connected only to the Cerbo (and thereby also the N2K network), and just obsolete the original fuel gauge. Then there are a few others, like the Safiery gauge, Holly Lidar etc; these would have to go through a Tank140 unit. etc etc
So with respect to your reply and specific comment about voltage on the tank inputs damaging the Cerbo, do you happen to know this for a fact? And would that still apply to only occasional application of voltage ie the few times I would operated the rocker switch to get a reading on the dashboard gauge, but the rest of the time having those levels available all the time at the Cerbo/N2K network?
Sorry for the rambling; if it sounds like a bit of a convoluted situation, that’s because it is.
Thx again for your time…
In theory, it is possible to physically connect a 33-240 Ohm tank sender to both an NMEA system and a Cerbo GX.
In this case, you can use a double-pole ON-OFF-ON switch and connect the 2 wires of the tank sender to the 2 input connections of the switch.
With the switch in the ON position (1), you can route the 33-240 Ohm resistor directly to a tank input of the Cerbo GX.
With the switch in the ON position (2), you can route the tank sender to the measurement circuit of the NMEA system.
In the OFF position, nothing is done with the tank sender resistor.
At the cheaper end of the scale WEMA make good senders that you can connect directly to the Cerbo contacts.
At the more expensive end there are the gobius ones that use some form of radar, they are now supported in the Cerbo
You can also get senders from Maretron which can connect directly to the NMEA2000 network, and then you can read the data in the cerbo from that network.
Thx all for comments. I’m aware of the option to use a switch to “choose”, but the whole exercise is one of convenience. So the objective is to be able to retain the existing dashboard functionality and ADD the Cerbo/N2K access. Doesn’t seem like a simple paralleling will be possible, so am just going to replace existing senders with new KUS units and connect them directly to then Cerbo. That will give me access through VRM and when underway on my Raymarine MFD via the Cerbo to N2K connection.