Seatalk failure - low voltage problem

[Robih]

I’d be grateful for any assistance from those more knowledgeable than me. Started up today to have low voltage alarm on the st60 graphic and no depth display. Autopilot control head displayed “seatalk failure”. Voltage displayed on the st60 graphic was 8.4v. I checked house batteries, showing 13.6v (alternator producing power). The E120 wouldn’t power up. Slowly the voltage showing on the st60 graphic increased to 9.5v. The E120 now switched on okay which (seemed to) cause the voltage on the st60 graphic to increase to 12.3v. Low voltage alarm silenced, depth display came up. I tested the V at the 12v panel isolator which provides power to the autopilot - reading 13.6v. Autopilot head displayed “standby” but wouldn’t engage autopilot on pressing “Auto”. Pulled the anchor up and noticed the St60 graphic voltage dropped from 12.3v to 11.9v as the windlass was energised. Moved to new anchorage. Opened up autopilot computer. Tested voltage at power supply - 13.1v (engine now off), see below:

Noticed the slightly weird wiring on the seatalk out from the computer with a chocolate box connector apparently having something piggy backing on to it. See picture enlarged from above:

I tested the voltage either side of the “weird thing”. Voltage coming out of the pilot computer is 13.0v, voltage downstream of said weird thing is 12.2v.

Could the weird thing be causing the problem? It’s almost as though something needs to be “charged up“ or “warmed up“ (like the old valve tellys) before enough voltage is delivered to seatalk.

As you can tell, this is beyond my pay grade, but if anyone can offer some gems of knowledge/guidance I’d be grateful.

Rob

ps - the boat is new to me so don’t know the history behind the wiring

pps - noticing as I sit here that the st60 graphic voltage is falling again, now 11.8v whereas with solar out our batteries are currently at 13.08v, charging 2.9A.

 

[Alex_Blackwood]

I’d be grateful for any assistance from those more knowledgeable than me. Started up today to have low voltage alarm on the st60 graphic and no depth display. Autopilot control head displayed “seatalk failure”. Voltage displayed on the st60 graphic was 8.4v. I checked house batteries, showing 13.6v (alternator producing power). The E120 wouldn’t power up. Slowly the voltage showing on the st60 graphic increased to 9.5v. The E120 now switched on okay which (seemed to) cause the voltage on the st60 graphic to increase to 12.3v. Low voltage alarm silenced, depth display came up. I tested the V at the 12v panel isolator which provides power to the autopilot - reading 13.6v. Autopilot head displayed “standby” but wouldn’t engage autopilot on pressing “Auto”. Pulled the anchor up and noticed the St60 graphic voltage dropped from 12.3v to 11.9v as the windlass was energised. Moved to new anchorage. Opened up autopilot computer. Tested voltage at power supply - 13.1v (engine now off), see below:

Noticed the slightly weird wiring on the seatalk out from the computer with a chocolate box connector apparently having something piggy backing on to it. See picture enlarged from above:

I tested the voltage either side of the “weird thing”. Voltage coming out of the pilot computer is 13.0v, voltage downstream of said weird thing is 12.2v.

Could the weird thing be causing the problem? It’s almost as though something needs to be “charged up“ or “warmed up“ (like the old valve tellys) before enough voltage is delivered to seatalk.

As you can tell, this is beyond my pay grade, but if anyone can offer some gems of knowledge/guidance I’d be grateful.

Rob

ps - the boat is new to me so don’t know the history behind the wiring

pps - noticing as I sit here that the st60 graphic voltage is falling again, now 11.8v whereas with solar out our batteries are currently at 13.08v, charging 2.9A.

Sorry I can't help with your voltage problem, however, the "Weird" thing is a Diode and a voltage drop of around 0.5 - 0.7 volts is expected. looks additional and not original but why is anyone's guess so I would be loath to tamper. It may be there to stop a pulse, such as from a relay switching off, from damaging something in the computer.
May be an idea to start looking for bad connections around the system. Start at the beginning and check connections and measure voltages to see if anything alters at any specific point.

 

[Robih]

Sorry I can't help with your voltage problem, however, the "Weird" thing is a Diode and a voltage drop of around 0.5 - 0.7 volts is expected. looks additional and not original but why is anyone's guess so I would be loath to tamper. It may be there to stop a pulse, such as from a relay switching off, from damaging something in the computer.
May be an idea to start looking for bad connections around the system. Start at the beginning and check connections and measure voltages to see if anything alters at any specific point.

Thanks Alex, yes I am loathe to remove the diode (thanks) without good reason, as tempting as it is!

 

[Bob_Ranft]

Maybe totally non related, but check the two blade fuses. Had problem with smart pilot continually dropping out of auto to standby. The two blade fuses where slack in their holders, causing intermittent contact. Bent the blades on the fuses very slightly to ensure they fitted tight into the holders, no problems since.

 

[john_q]

I’d be grateful for any assistance from those more knowledgeable than me. Started up today to have low voltage alarm on the st60 graphic and no depth display. Autopilot control head displayed “seatalk failure”. Voltage displayed on the st60 graphic was 8.4v. I checked house batteries, showing 13.6v (alternator producing power). The E120 wouldn’t power up. Slowly the voltage showing on the st60 graphic increased to 9.5v. The E120 now switched on okay which (seemed to) cause the voltage on the st60 graphic to increase to 12.3v. Low voltage alarm silenced, depth display came up. I tested the V at the 12v panel isolator which provides power to the autopilot - reading 13.6v. Autopilot head displayed “standby” but wouldn’t engage autopilot on pressing “Auto”. Pulled the anchor up and noticed the St60 graphic voltage dropped from 12.3v to 11.9v as the windlass was energised. Moved to new anchorage. Opened up autopilot computer. Tested voltage at power supply - 13.1v (engine now off), see below:

Noticed the slightly weird wiring on the seatalk out from the computer with a chocolate box connector apparently having something piggy backing on to it. See picture enlarged from above:

I tested the voltage either side of the “weird thing”. Voltage coming out of the pilot computer is 13.0v, voltage downstream of said weird thing is 12.2v.

Could the weird thing be causing the problem? It’s almost as though something needs to be “charged up“ or “warmed up“ (like the old valve tellys) before enough voltage is delivered to seatalk.

As you can tell, this is beyond my pay grade, but if anyone can offer some gems of knowledge/guidance I’d be grateful.

Rob

ps - the boat is new to me so don’t know the history behind the wiring

pps - noticing as I sit here that the st60 graphic voltage is falling again, now 11.8v whereas with solar out our batteries are currently at 13.08v, charging 2.9A.

I have the same course computer but it does not have the “weird thing”.

 

[john_q]

What other devices are attached to the sea talk cable?

 

[earlybird]

As well as generally checking connections I'd remove the diode and at least test it with a DVM. Perhaps better still replace it with another, new diode. (Plenty on Ebay).
Actually, I'd be surprised if it's necessary.

 

[Robih]

Maybe totally non related, but check the two blade fuses. Had problem with smart pilot continually dropping out of auto to standby. The two blade fuses where slack in their holders, causing intermittent contact. Bent the blades on the fuses very slightly to ensure they fitted tight into the holders, no problems since.

Will check, thanks.

 

[Robih]

What other devices are attached to the sea talk cable?

The normal Seatslk kit - Speed, Depth, Wind and an MFD.

 

[Robih]

As well as generally checking connections I'd remove the diode and at least test it with a DVM. Perhaps better still replace it with another, new diode. (Plenty on Ebay).
Actually, I'd be surprised if it's necessary.

I presume testing the diode is a matter of checking resistance in both directions, with one direction being very low resistance and the other direction very high resistance?

 

[Robih]

I have the same course computer but it does not have the “weird thing”.

Nor did the S2G computer on my last boat, I've never before read of a necessity for a diode on the seatalk circuit.

 

[Alex_Blackwood]

I presume testing the diode is a matter of checking resistance in both directions, with one direction being very low resistance and the other direction very high resistance?

From the volt drop reading he is getting , approx. 0.8 volts , one would say that the diode is OK. If the diode was defective he would either have no volt drop or no volts! It would be open circuit or shorted. Without actually seeing the installation it is again impossible to say why it has been fitted. Could be because some other bit of kit has been causing a spike on the circuit (the MFD?). I would have thought unlikely on "Seatalk", more likely on the supply. However, I am not sufficiently familiar with it to pass any other opinion. Personally I would want to investigate. Having said all that. It may be worth monitoring the volt drop across the diode and see if it changes in line with the problem. Very remote possibility that the diode is altering with heat. I cannot see what voltage or current rating that diode is. worth checking that as well.

 

[Hoolie]

If you're replacing the diode, use a Schottky diode as the voltage drop at low current levels is much less than a standard one. I agree it's probably been fitted to protect the unit from transient voltage spikes and using a Schottky won't do any harm.

 

[Robih]

Update: Just about to start dealing with the suggestions above so turned seatalk network on. Low volts alarm sounded and displayed 8.4v for about ten seconds then jumped to 12.8v. I have the genny running so batteries at 14v.

 

[Hoolie]

Where is your Seatalk 12v supply connected? I know the Smart Pilot range can be configured to power the whole network and maybe that's how yours is connected. In my view that's a bit restrictive as you need the AP to be powered up whenever you want the other instruments. Maybe a second 12v ( switched) connection would be better and might solve your low voltage problem?

 

[Robih]

Where is your Seatalk 12v supply connected? I know the Smart Pilot range can be configured to power the whole network and maybe that's how yours is connected. In my view that's a bit restrictive as you need the AP to be powered up whenever you want the other instruments. Maybe a second 12v ( switched) connection would be better and might solve your low voltage problem?

Investigation this morning identifies that the st60’s receive power from two sources - the smart pilot and the MFD. Seemingly this morning the st60’s received a supply of 12.8v from the smart pilot but the MFD seems only to supply 9v. So, suspicion now falls upon the MFD supply for further testing. But this doesn’t explain why yesterday I had only 8v showing when both a/p and MFD were on and supplying power. Perhaps the supply from the a/p is subject to delay for some reason?

I think the idea of an independent pure 12v supply is a good one, as you say it might solve the low V problem. If the MFD testing reveals nothing further then I will try this route.

 

[Hoolie]

It seems to me that not only does your network have two power sources but the power line is split into two zones. You really can't have 12v at on end of a line and 9v at the other. Try turning off the AP and see which instruments are still active. Likewise with the MFD. If it is zoned then the problem, as you've described it, is with the MFD outputting low volts. Disconnect its 12v to Seatalk and wire a direct 12v connection then you should be good to go!

 

[PaulRainbow]

I think the idea of an independent pure 12v supply is a good one, as you say it might solve the low V problem. If the MFD testing reveals nothing further then I will try this route.

I would remove the diode (this is a bodge, for some unknown reason) and the short red wire, but leave the choc block for now, so no power connection to/from the AP.

Disconnect the red wire from the MFD too, so no power there either.

At this point in time, the ST60s etc should not power up. ***

Connect a fused positive wire to the wire that was connected to the chart plotter, the choc block at the AP or anywhere else on the ST network that is the most convenient. Everything should now work properly. If not check all connections, especially the negative wiring to the ST network. When things are working as they should, fit a switch in the new power supply wire. You can now power the ST network on its own, so you can just see depth/wind etc. When you want to use the AP you obviously need to turn the ST network on too.

*** Edit If only some devices power up, bridge the positive connection between the last device that works and the first that doesn't.

 

[PaulRainbow]

If you're replacing the diode, use a Schottky diode as the voltage drop at low current levels is much less than a standard one. I agree it's probably been fitted to protect the unit from transient voltage spikes and using a Schottky won't do any harm.

The diode is a bodge, it shouldn't be there, best fix the underlying problem.

It seems to me that not only does your network have two power sources but the power line is split into two zones. You really can't have 12v at on end of a line and 9v at the other. Try turning off the AP and see which instruments are still active. Likewise with the MFD. If it is zoned then the problem, as you've described it, is with the MFD outputting low volts. Disconnect its 12v to Seatalk and wire a direct 12v connection then you should be good to go!

Tis an odd looking setup. You can't have two power supplies on a ST nertwork, it causes problems (might explain the diode). If it's as you suggest, split into two "zones" it's still odd and i'd correct it by disconnecting the MFD supply and fitting a direct 12V supply, as you suggest. I would disconnect the AP diode though, if some of the instruments then won't power up, bridge the positive ST wiring between the last device that works and the first one that doesn't.

 

[Robih]

I would remove the diode (this is a bodge, for some unknown reason) and the short red wire, but leave the choc block for now, so no power connection to/from the AP.

Disconnect the red wire from the MFD too, so no power there either.

At this point in time, the ST60s etc should not power up. ***

Connect a fused positive wire to the wire that was connected to the chart plotter, the choc block at the AP or anywhere else on the ST network that is the most convenient. Everything should now work properly. If not check all connections, especially the negative wiring to the ST network. When things are working as they should, fit a switch in the new power supply wire. You can now power the ST network on its own, so you can just see depth/wind etc. When you want to use the AP you obviously need to turn the ST network on too.

*** Edit If only some devices power up, bridge the positive connection between the last device that works and the first that doesn't.

Paul,

Thanks, that gives me the confidence to ditch the diode and see what happens. Will report back.