Power drain switching off chartplotter - diodes?

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All_at_Sea

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When l use the bowthruster the chartplotter goes off or resets to start. Presumably because the bowthruster is using so many amps that that takes precedent over anything else using the battery.

My question is about diodes - would one work if l put it in line to stop the 'back flow' when the bowthruster is activated? Failing that do l need to route the chartplotter a different way to get power in the first place? I will go to the boat in minute to see where the power is taken off the system and try and work out what to do but is a diode the answer?
 
All_at_Sea said:
When l use the bowthruster the chartplotter goes off or resets to start. Presumably because the bowthruster is using so many amps that that takes precedent over anything else using the battery.

My question is about diodes - would one work if l put it in line to stop the 'back flow' when the bowthruster is activated? Failing that do l need to route the chartplotter a different way to get power in the first place? I will go to the boat in minute to see where the power is taken off the system and try and work out what to do but is a diode the answer?
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Is the bowthruster powered by the main domestic batteries? If so, diodes won't help, you either need to increase the capacity of your domestic bank or install a dedicated thruster battery.
 
pvb said:
Is the bowthruster powered by the main domestic batteries? If so, diodes won't help, you either need to increase the capacity of your domestic bank or install a dedicated thruster battery.
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Or a dedicated plotter battery, which need only be a small one as used in alarms etc.
 
Diodes will not help on their own but you could make a connection to the engine battery as per the link in post #2.

If the thruster is connected to the domestic bank, without it's own battery, you could move the connection to the engine battery. It won't flatten the engine battery, the engine will be running and the thruster won't run for long enough to flatten it, unless it's an awfully feeble engine battery (in which case don't bother).
 
pvb said:
Yes, but then you've ideally got to arrange some sort of echo-charge system for it.
Click to expand...

Same problem as adding a thruster battery, but on a small scale.
some people used to like having the VHF and GPS on an independent batt, IIRC some racing instructions used to encourage it?
Small batteries are fussier about charging though. You don't want to be shoving in 14.4V for extended periods.

LDO float regulator and 'a few diodes' is one answer, perhaps.
 
lw395 said:
Same problem as adding a thruster battery, but on a small scale.
Click to expand...

Not sure it is the same. If the thruster is currently fed from the domestic bank, then there should be adequate cables in place already. All that needs to be done is to add a thruster battery, close to the thruster, which should minimise voltage drop in the domestic bank. For safety, an additional fuse will be needed in the main cable at the thruster end.
 
pvb said:
Not sure it is the same. If the thruster is currently fed from the domestic bank, then there should be adequate cables in place already. All that needs to be done is to add a thruster battery, close to the thruster, which should minimise voltage drop in the domestic bank. For safety, an additional fuse will be needed in the main cable at the thruster end.
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If there are fat cables and big batteries already, you need to do the math to see how adding one more battery will affect the voltage drop.
Preferably do the math for when the thruster batt is getting near the end of its life.
The house batts will still contribute a lot of current if the cable is fat. So the volts will still be pulled down, just not so much!

It can also depend on whether it's the start surge or the running current of the thruster that kills the plotter. The capacitors in the plotter may hold it up for the 1s start surge, but not the 20s running burst. Or not!

It can actually be quite a subtle problem and may vary a lot from boat to boat.
Life would be a lot easier if marine stuff was better designed to cope with this kind of problem.

Of course one could ask why we need a plotter when we are close enough to the dock to be using a thruster....
 
lw395 said:
Of course one could ask why we need a plotter when we are close enough to the dock to be using a thruster....
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True, however after a long day out sailing it's annoying to find once moored up the chartplotter has gone out. On setting out l tend to get everything ready for the off only to have to re-start the chartplotters (one below and one in cockpit). Not a huge issue l agree but want to find some sort of fix. So it would seem voltage drop is the problem. I do have a dedicated thruster battery but this must be linked to my other domestic battery in some way (maybe for charging). I wonder of the batteries are just old and not holding proper charge......
 
When I mounted my Garmin in the cockpit, I decided to save the hassle of running separate power, and took the power from the engine key switch. Same problem as you, every time I started the engine, so I had to do what I should have done first time and ran a power supply from the domestic bank. Your plotters switch off because the voltage drop when you use your bow thruster means the supply drops below minimum voltage...
 
All_at_Sea said:
True, however after a long day out sailing it's annoying to find once moored up the chartplotter has gone out. On setting out l tend to get everything ready for the off only to have to re-start the chartplotters (one below and one in cockpit). Not a huge issue l agree but want to find some sort of fix. So it would seem voltage drop is the problem. I do have a dedicated thruster battery but this must be linked to my other domestic battery in some way (maybe for charging). I wonder of the batteries are just old and not holding proper charge......
Click to expand...

That would usually be done using a diode or VSR to charge the thruster battery from the domestic bank. If you have heavy cables from the domestic bank to the thruster battery that won't be so simple to do. My vote would still be to connect the thruster battery to the engine battery. It would cure the plotter problem, would not run the engine battery down as the engine will be running and both the engine and thruster batteries should both be fully charged. If it's connected straight to the domestic batteries (which it must be to give the plotter problem) then if you've been out for a while the domestic batteries will have been taking power from the thruster battery, using the thruster to moor will then be taking more power from the domestic bank, which you may well need whilst moored.
 
PaulRainbow said:
That would usually be done using a diode or VSR to charge the thruster battery from the domestic bank. If you have heavy cables from the domestic bank to the thruster battery that won't be so simple to do. My vote would still be to connect the thruster battery to the engine battery. It would cure the plotter problem, would not run the engine battery down as the engine will be running and both the engine and thruster batteries should both be fully charged. If it's connected straight to the domestic batteries (which it must be to give the plotter problem) then if you've been out for a while the domestic batteries will have been taking power from the thruster battery, using the thruster to moor will then be taking more power from the domestic bank, which you may well need whilst moored.
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Agree, seems the original installation may not have been thought out very thoroughly.
 
All_at_Sea said:
True, however after a long day out sailing it's annoying to find once moored up the chartplotter has gone out. On setting out l tend to get everything ready for the off only to have to re-start the chartplotters (one below and one in cockpit). Not a huge issue l agree but want to find some sort of fix. So it would seem voltage drop is the problem. I do have a dedicated thruster battery but this must be linked to my other domestic battery in some way (maybe for charging). I wonder of the batteries are just old and not holding proper charge......
Click to expand...

I guess it's more annoying when it switches off just as you leave the pontoon?
I had this on my old boat with a Garmin 120 and the old 1-2-both switch.
An old motorbike battery and some schottky diodes cured it for almost no outlay, but there are more elegant solutions.

The thruster batt also gives the thruster more beans when it starts of course.
 
PaulRainbow said:
That would usually be done using a diode or VSR to charge the thruster battery from the domestic bank. If you have heavy cables from the domestic bank to the thruster battery that won't be so simple to do. My vote would still be to connect the thruster battery to the engine battery. It would cure the plotter problem, would not run the engine battery down as the engine will be running and both the engine and thruster batteries should both be fully charged. If it's connected straight to the domestic batteries (which it must be to give the plotter problem) then if you've been out for a while the domestic batteries will have been taking power from the thruster battery, using the thruster to moor will then be taking more power from the domestic bank, which you may well need whilst moored.
Click to expand...

Either the cables must be man enough to run the thruster, or you need some other approach to be sure the thruster current is not overloading anything in the event the thruster battery is flat or at the end of its life.
E.g. a VSR with a current limit.
Or a current limited charging circuit for the thruster battery.
Bearing in mind the alternator will want to keep everything up at 14.4V or so, if the engines running, so the full current of the alternator will go to the bow unless something limits it.
The actual Ah taken by the thruster should not be significant unless you are having a bad day at parking in a strong cross wind.
 
All_at_Sea said:
True, however after a long day out sailing it's annoying to find once moored up the chartplotter has gone out. On setting out l tend to get everything ready for the off only to have to re-start the chartplotters (one below and one in cockpit). Not a huge issue l agree but want to find some sort of fix. So it would seem voltage drop is the problem. I do have a dedicated thruster battery but this must be linked to my other domestic battery in some way (maybe for charging). I wonder of the batteries are just old and not holding proper charge......
Click to expand...

Many years ago Sealine had a problem with nav equipment dropping out due to low voltage during engine start, one engine battery bank supplying engine and domestic power. Solved it by making a power supply that drew power from the battery bank with the highest voltage and fed nav equipment, i.e the engine bank not supplying domestic power, during engine start.

Can you use a soldering Iron ?

Brian
 
lw395 said:
Either the cables must be man enough to run the thruster, or you need some other approach to be sure the thruster current is not overloading anything in the event the thruster battery is flat or at the end of its life.
E.g. a VSR with a current limit.
Or a current limited charging circuit for the thruster battery.
Bearing in mind the alternator will want to keep everything up at 14.4V or so, if the engines running, so the full current of the alternator will go to the bow unless something limits it.
The actual Ah taken by the thruster should not be significant unless you are having a bad day at parking in a strong cross wind.
Click to expand...

But as his current system works OK, apart from turning the plotter off, all he needs to do is swap the cables over to the engine battery and the problem is solved.
 
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