Chartplotter turns off on engine start

[GrahamHR]

Honestly, the small 12v battery and diode solution is cheap and works really well.

It also means the chart plotter works without the main battery switch in the "on" position, e.g. when you're playing with it, boat in the drive or yard, wishing you are at sea, with the main batteries removed for the winter.

PS I think I knoe "Beyondtheblue" from an American boat owners forum and of course ther's nothing wrong with that!

Graham

 

[beyondtheblue]

Hi Graham... small world!

 

[William_H]

Batteries

Firstly always starting on "both" position is a bad habit. Sure it means when the engine starts charging it charges both nicely. What it does not do is test the engine battery as to it's ability to start the engine. Time will come when one battery is not able to start the engine because of old age. If you continue to use both then you will not know you have a problem until both batteries are too old to start the engine.

Best arrangement is a specialised start battery for the engine and a specialised deep cycle battery for services. Always start on the engine battery and occasionally start on the service battery to ensure it is can do the job. After all you have 2 batteries to give you a backup in case of battery failure and a service battery so that you can discharge it while retaining an isolated start battery to get you going.

In the meantime you should regularly start on either battery alone then switch to both for charging. You must go to one battery if you are going to be using power without engine running to isolate the battery being discharged from that you need for engine start.

If you want to continue using 1,2,both switch and identical batteries you could supply the electronics via 2 diodes one from each positive supply so that when on battery ons tarting drops in voltage the other battery will supply.
Or you could use the additional battery (tiny SLA alrm battery) isolated by diode as supply for plotter etc. Doing this you need to be aware that you must turn off the plotter and not rely on turnning main power off when you leave the boat. These little batteries will drop dead if you heavily discharge them as in leaving plotter on all week.
The more reliable and simplest fix is using a large capacitor in lieu of a small battery. A silican diode rated at a few amps is wired in the supply line anode to supply cathode (band or head of arrow) to the plotter. A capacitor of 10000microfarrad rated at more than 18 volts is wired from the plotter input +ve to -ve earth. A larger capacitor might even be better and smaller ones can be wired in parallel to increase capacitance.
A capacitor will last many years and is not harmed by being completely discharged. olewill

 

[Refueler]

Have the same problem. Talked with a technicien and problem is probably the wiring. Wiring in general is too thin, so replacement of the wiring (from battery to the main board) to ie 70 mm is the solution.

grtz

Sorry to argue with your guy .... but it often makes no difference how large a cable you fit ... it's the physical demand of the engine starter that determines the voltage drop and possible below the minimum req'd to run the plotter. Some plotters / instruments are more sensitive to this than others of same make ... if you watch a voltmeter while cranking an engine - it can drop to 9V even ... many instruments will cop out at about 10V or even slightly higher.
The trick is to boost that voltage to keep it above minimum req'd ... or separate supplies.

My plotter has for years been fed direct of domestic with own main switch etc. so that I don't have this problem - which I did have on previous.

 

[lw395]

It's particularly annoying when you turn the motor on as you approach a difficult bit of pilotage after a day's sail. You want to be able to ask the crew to start the motor without having to fiddle with switches, or remember to push the 'on' button of the garmin.
I used a small sealed 12V batt to power the Garmin, but some care is needed as these little 12V's don't like seeing 14+ volts of boost charge when the engine is running. OTOH they tend not to take much charge if there is an extra diode drop in the way. You may find the small battery goes flat after a while. I think if I were starting again, I'd have a 3 battery system or a solar trickle charge for the instrument battery.
A diode and capacitor solution may need a very big cap, as some plotters use a surprising amount of current.

 

[Refueler]

It's particularly annoying when you turn the motor on as you approach a difficult bit of pilotage after a day's sail. You want to be able to ask the crew to start the motor without having to fiddle with switches, or remember to push the 'on' button of the garmin.
I used a small sealed 12V batt to power the Garmin, but some care is needed as these little 12V's don't like seeing 14+ volts of boost charge when the engine is running. OTOH they tend not to take much charge if there is an extra diode drop in the way. You may find the small battery goes flat after a while. I think if I were starting again, I'd have a 3 battery system or a solar trickle charge for the instrument battery.
A diode and capacitor solution may need a very big cap, as some plotters use a surprising amount of current.

Actually I was suprised when I spoke to an electronics guy and he reckoned you didn't need a huge capacitor ... as the culprit that causes the plotter / instrument to go off is only a very short duration event. The battery sees a stopped engine and starter ... it has to get that lot going and it suffers a huge draw to get it going ... once starter / engine is turning the draw is a lot less ... so it's that initial OOMPH needed from battery that clicks out the gear ... the capacitor will be enough for that very short period.

Once I knew about it ... I started to realise why so many articles have cap's fitted ...

 

[lw395]

Actually I was suprised when I spoke to an electronics guy and he reckoned you didn't need a huge capacitor ... as the culprit that causes the plotter / instrument to go off is only a very short duration event. The battery sees a stopped engine and starter ... it has to get that lot going and it suffers a huge draw to get it going ... once starter / engine is turning the draw is a lot less ... so it's that initial OOMPH needed from battery that clicks out the gear ... the capacitor will be enough for that very short period.

Once I knew about it ... I started to realise why so many articles have cap's fitted ...

OK, you win, I will stop being lazy and do the sums:
Assume GPS 150mA ( flashy colour plotter will be more)
Dropout Voltage 9V
Initial system voltage 12.5V Diode drop reduces this to 11.9 on capacitor.
Cranking time 15 seconds (guess!)
15 seconds x 150mA = 2.25 Coulomb
11.9 to 9 V = 2.9V fall
Capacitance= charge/ delta V = 2.25/2.9 =0.77Farad

I think that's pretty big. thousands of microfarads is common, you can get 1 Farad caps, they are not cheap though!
Scale the above with your own assumptions.

Cranking voltage will often be below 9V, particularly if the battery has been discharged a bit, like if its been running the fridge or just a day's sailing.
I would want to design something that coped with reasonable adversity, such as when the engine takes a bit longer to fire for some reason.
Cranking voltage specs on a new, fully charged, battery are often 1.5V per cell i.e 9V, or 1.2VPC= 7.2V, and you need a diode drop to stop the cranking flattening the capacitor. A lot of us go on using batteries long after they don't meet specs!

Not sure what the most elegant solution is, perhaps change psu in the garmin to work lower?
I don't mind it stopping working for a few seconds,, it's having to remember to switch it back on and wait for it to boot up that was a wind up.

 

[William_H]

Re IW395 calculations

The calculations are impressive however you have taken the battery to be at 9V for 15 secs. Here I agree with Refueler the voltage on many engines won't stay so low for that long. Much depends on how fast the engine starts I would normally expect about 3 secs and the current drain of the starter will reduce as the engine cranks over. So we might be able to reduce the C required from your calculations to perhaps 100000 microfarrads. I think that perhaps actual experimentation would be the way to go. You could start with 10000 and add more in parallel until you get the desired results. Perhaps someone has actual experience?
olewill

 

[GrahamHR]

The small sealed lead acid battery/ diode set up has lasted me 3 years. Admitedly, I remove the chartplotter when I leave the boat, so it never goes flat (I do that so so the chartplotter is impossible to steal!). Still, the battery has survived 3 X 6 winter months without charge. A pretty cheap fix that works in my opinion, or rather experience.

 

[cozzykim]

The calculations are impressive however you have taken the battery to be at 9V for 15 secs. Here I agree with Refueler the voltage on many engines won't stay so low for that long. Much depends on how fast the engine starts I would normally expect about 3 secs and the current drain of the starter will reduce as the engine cranks over. So we might be able to reduce the C required from your calculations to perhaps 100000 microfarrads. I think that perhaps actual experimentation would be the way to go. You could start with 10000 and add more in parallel until you get the desired results. Perhaps someone has actual experience?
olewill

+1, and the initial large volt drop may be due to mechanical inertia, only a fraction of a second, it's worth trying a smallish capacitor to start with IMO.

Just for the record (OK it's only 5V but you get the drift )

 

[lw395]

+1, and the initial large volt drop may be due to mechanical inertia, only a fraction of a second, it's worth trying a smallish capacitor to start with IMO.

Just for the record (OK it's only 5V but you get the drift )

5v supercaps are a special case. One of those at the GPS processor would do the trick for sure. Shame Garmin and co don't design something in. After all, if my £90 tomtom has an internal battery.....
If you look on ebay 1Farad 15 Volt caps go for about £30. They are used by car audio nutters.

You have to decide if you want a solution which works best case, most of the time or worst case.
I fully agree that the engine will often start in a few seconds without pulling the volts so low.
But imho worst case is that it won't, and that's the time when I really don't want to be mucked around by the instruments.
A good solution is to feed a capacitor via diodes and fuses from both batteries, that way the GPS will run off whichever is highest volts. But in doing so you have compromised your battery isolation (hence the fuses, which should be close to the battery). Maybe a separate two pole isolator switch would be nice? I did at one point have a navtex running of a separate switch, but in general I like to isolate everything when I leave the boat.

We should also be aware of potential issues where if the GPS is powered, but other instruments connected to it via NMEA (etc) are not, then current may flow via the data link. This may not be desirable, it can cause some instruments to lock up until fully powered off and on again. I suspect this can apply to certain repeaters, but have not diagnosed it fully. This is partly why some people have opto-isolators in the data lines. I once had a situation where I could not get the depth sounder to read, and this may have been the cause. Or not!

Hope this is helpful.

 

[Refueler]

OK, you win, I will stop being lazy and do the sums:
Assume GPS 150mA ( flashy colour plotter will be more)
Dropout Voltage 9V
Initial system voltage 12.5V Diode drop reduces this to 11.9 on capacitor.
Cranking time 15 seconds (guess!)
15 seconds x 150mA = 2.25 Coulomb
11.9 to 9 V = 2.9V fall
Capacitance= charge/ delta V = 2.25/2.9 =0.77Farad

I think that's pretty big. thousands of microfarads is common, you can get 1 Farad caps, they are not cheap though!
Scale the above with your own assumptions.

Cranking voltage will often be below 9V, particularly if the battery has been discharged a bit, like if its been running the fridge or just a day's sailing.
I would want to design something that coped with reasonable adversity, such as when the engine takes a bit longer to fire for some reason.
Cranking voltage specs on a new, fully charged, battery are often 1.5V per cell i.e 9V, or 1.2VPC= 7.2V, and you need a diode drop to stop the cranking flattening the capacitor. A lot of us go on using batteries long after they don't meet specs!

Not sure what the most elegant solution is, perhaps change psu in the garmin to work lower?
I don't mind it stopping working for a few seconds,, it's having to remember to switch it back on and wait for it to boot up that was a wind up.

Judging by the people who have fitted cap's to stop this 'drop-out' of instruments - I would suggest that your calc's are way of the mark. Just reading through - I have 1 part that immediately shows error ... the time taken to crank and power ( V drop ) ... it's nowhere near 15 secs ... not even 1.5 secs ...

As told to me - the critical time is the INITIAL jolt to get engine / starter to turn. Once turning the battery recovers some of it's voltage quickly. It is true that throughout the cranking that battery will be lower in Volts than it's rested state, but higher than the first initial when button pressed. If you have a voltmeter - preferably analogue - you will likely see that needle for a fraction of a second dip very low when you hit the start ... then coming back up to nearer 10.5V while starter is now doing less work keeping engine turning

Well that's as shown / explained to me ...

Considering the price of small SLA batterys now that House Alarm systems are common - it's cheap enough to have a dedicated SLA and forget all this. Maplins will provide suitable charger etc. that can charge from 12v / Engine alternator ... or you could have a "make before break" change switch ?

Many cheap low tech solutions available.

 

[Skylark]

What a great thread. Why wasn't it started in April!

I'm going to try the capacitor route first. Then a small alarm-type battery if the capacitor doesn't solve my problem. I've just bought a 10,000 micro Farrad 40v capacitor from e-bay. Will not be able to try it until Easter.

 

[fergie_mac66]

Im sure it wont be this so i hesitate to say but years ago I was on a boat when a fault occurred on the regulator on the alternator when the engine started it gave a 20 volt pulse which switched the depth sounder off eventually it blew the internal reg' in the depth sounder and it only worked with batteries from then on

 

[Dipper]

Last November I posted that my GPS turns off when I start the engine.

Over the winter I tidied up the spaghetti junction of old battery cables and fitted new ones and a new battery switch. I also shortened the main cables supplying the main switch panel and made better connections. This was done as a project on its own but I have now found out that the GPS no longer switches off when I start the engine which was a pleasant surprise.

This fits in with the comments from other posters about low voltage being a probable cause of the fault.

 

[whaler]

I just built the capacitor/diode assembly for about $25 and was delighted to find that it solved a 4-yr old "plotter shutdown on engine start" problem on a twin-diesel 40-ft whalewatching boat that I drive. It's not my boat and I couldn't convince the owner to put in an isolated battery for the electronics. So it was on my "dime & time" and I'd been looking for a cheap & quick fix. Adding a 10,000-mfd 63-volt capacitor and two 6-amp diodes (wired in parallel to give 12 amps) seems to have done the trick. I wired it into a box with a bypass switch to appease the boss if my add-on stops functioning for any reason.

Many thanks to the forum for the suggestion!