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Help setting up MFDs
Posted: Tue May 03, 2022 10:03 pm
by fallguy1000
So, the Skoota has two MFDs, or multi-function displays.
One is a Furuno tzt12l or something close.
The other is a Raymarine Axiom 9 Pro.
The Furuno says it has a 1.2A draw at 24v.
The Raymarine is protected by a 15 amp in line fuse...
I find it super hard to believe the Raymarine draws 15amps!
Here is the spec. It says 20 watts. At 24vdc supply, this is under a 1 amp draw...
https://www.raymarine.com/multifunction ... /pro9.html
Anyone have any idea why they would go so far over draw with a fuse?
I need to source the device and the in-line fuse doesn't meet the ABYC 7" rule as fused, so I typically would fuse the device off my own fuse block and I'm thinkin I'd drop it to 2 amp and call it good.
Anyhow, Jaysen, or anyone else, if you get why they'd fuse so far over rated draw, let me know. In rush? All components are rated for 32v, so why not?
Re: Help setting up MFDs
Posted: Wed May 04, 2022 7:50 am
by jonnymac
I can’t see a reason, 150% of normal load is max i would go. two questions, are you sure its 15 and not 1.5, and are you sure its the stock fuse?
edit for clarity and to add this:
inrush is managed by how fast a fuse will blow not its amp rating, so a slow fuse handles more inrush.
fallguy1000 wrote: ↑Tue May 03, 2022 10:03 pm
So, the Skoota has two MFDs, or multi-function displays.
One is a Furuno tzt12l or something close.
The other is a Raymarine Axiom 9 Pro.
The Furuno says it has a 1.2A draw at 24v.
The Raymarine is protected by a 15 amp in line fuse...
I find it super hard to believe the Raymarine draws 15amps!
Here is the spec. It says 20 watts. At 24vdc supply, this is under a 1 amp draw...
https://www.raymarine.com/multifunction ... /pro9.html
Anyone have any idea why they would go so far over draw with a fuse?
I need to source the device and the in-line fuse doesn't meet the ABYC 7" rule as fused, so I typically would fuse the device off my own fuse block and I'm thinkin I'd drop it to 2 amp and call it good.
Anyhow, Jaysen, or anyone else, if you get why they'd fuse so far over rated draw, let me know. In rush? All components are rated for 32v, so why not?
Re: Help setting up MFDs
Posted: Wed May 04, 2022 11:29 am
by Jeff
FallGuy, Jaysen asked me to send you the following response: "Tell Fg1k that fuses are for preventing fire via overloaded wires and the gauge of wire, not the draw of the equipment sets the proper size for the fuze. The only exceptions would be extreme high draw devices (radar, radio, etc) that need to limit the output to the transmitter." Jeff
Re: Help setting up MFDs
Posted: Wed May 04, 2022 11:54 am
by fallguy1000
All that makes sense.
My kid told me they developed the 15a as a standard item to reduce cost and it should be protrcted lower.
Thanks for all the replies.
It is running well on 2 amp fusing.
Re: Help setting up MFDs
Posted: Thu May 05, 2022 5:51 pm
by Cbuf
Some MFD's have an aux power source to power other units, radar, transducers, and other networked devises. Meaning when you turn on the unit it turns on several other devises. the 15 amp might be for that, so while the unit only pulls 2 amp you could plug in an auto pilot unit that pulls another 4 amp, and a radar that pulls 7 amps, and a weather band unit that can pull another couple amps.
cbuf
Re: Help setting up MFDs
Posted: Fri May 06, 2022 5:13 pm
by jonnymac
I was thinking about this at work today, and the absolute max fuse size would be based on wire gauge and length of run, but that wouldn’t necessarily protect a device. so going conservative isn’t a bad thing if you have some spares to go up a few sizes if necessary
Re: Help setting up MFDs
Posted: Fri May 06, 2022 5:38 pm
by fallguy1000
jonnymac wrote: ↑Fri May 06, 2022 5:13 pm
I was thinking about this at work today, and the absolute max fuse size would be based on wire gauge and length of run, but that wouldn’t necessarily protect a device. so going conservative isn’t a bad thing if you have some spares to go up a few sizes if necessary
I was also trying to determine total expected draw on my 20 amp subpanel.
Turns out my draw is 12.68A at 24vdc.
Adding the Raymarine at 15A would be 27.67A, but that is completely irrational. I fused it at 2 like the Furuno and nothing blown thus far.
Thanks for all the replies. Still no idea on continuous rated current for the Raymarine. But it does have Netflix. Connection not good enough for it.