Engine Start Voltage Drop suppression

Andrew_Trayfoot said:
Quite a lot off faff to rewire the battery setup for one instrument.
I was wondering if there was some some electronics that wound hold the voltage up for 3 or 4 seconds.
Click to expand...
It’s not for one instrument though. It’s to ensure that the domestics don’t discharge your battery to the extent that they can’t then start the engine.
not an issue if you can manually start the engine but if you can’t.

That instrument turning off and associated voltage drop is a warning sign. Up to you if you ignore it.
 
You could try a diode and capacitor to hold up the voltage.
1685734107755.png
You would have to experiment to find the right value of capacitor. You could start with a 1000uF 25V electrolytic and see if it holds up for long enough. This obviously depends on the current drawn by the instrument.
If the capacitor is too large it will draw a momentary large current as it charges up when you switch on. This may take out your overcurrent trip or blow a fuse. Not an off the shelf solution as it needs setting up for your particular instrument.
If you are not an electronics geek with a handy box of capacitors, then this is probably not a solution for you.
 
Another solution for you. A DC-DC converter with a wide input voltage. This one works with 3V to 35V input and 5V to 40V output. DC-DC converter
The output voltage has to be higher than the input voltage so you may have to run your instrument at 18V. Check the handbook but most instruments are OK with this.
Other DC-DC converters are available if you do a search you might find a more suitable one.
 
You could try running a separate supply directly from the battery so that none of the wiring is shared with the starting circuit. That is a very simple test to do and might be enough to stop the instruments cutting out
 
Andrew_Trayfoot said:
Quite a lot off faff to rewire the battery setup for one instrument.
I was wondering if there was some some electronics that wound hold the voltage up for 3 or 4 seconds.
Click to expand...
Not really. Replace the 1.2,both with something like a BEP switch cluster which gives you individual circuits, VSR for split charging and and a parallel switch. Basic small car battery for engine start and combine your current 2 batteries into one for domestics. Apart from solving the current problem, you will have enhanced domestic capacity and all your batteries will last longer because they are only doing one job.
 
So the setup is:
2 batteries: 1 110ah leasure(getting a bit tired), 1 cranking.
1,2, both switch.
Wiring is all up to or above spec.
Garmin GPS 126, FishFinder100, Matsutec HP33A AIS. All perfectly ok when starting the engine.
Owna KMR-6 drops out.

I tend to only use the engine battery to start from cold.

So the only current problem I have is the drop out of the Owna.

Might look at VSR etc next winter.
DC-DC converter and the diode/capacitor look interesting so will look at that.
 
andsarkit said:
You could try a diode and capacitor to hold up the voltage.
View attachment 157589
You would have to experiment to find the right value of capacitor. You could start with a 1000uF 25V electrolytic and see if it holds up for long enough. This obviously depends on the current drawn by the instrument.
If the capacitor is too large it will draw a momentary large current as it charges up when you switch on. This may take out your overcurrent trip or blow a fuse. Not an off the shelf solution as it needs setting up for your particular instrument.
If you are not an electronics geek with a handy box of capacitors, then this is probably not a solution for you.
Click to expand...
Nice diagram and quite right. would however suggest a larger capacitor. I don't think high in put surge current will be a problem . ol'will
 
I have a very similar setup to the OP.
What I have done is use the 1-both-2 switch for engine starting and charging only. I have a second 1-off-2 switch with a lower current rating to switch on the domestics. This means that the engine and domestics can run off different batteries and I have full control of the charging.
I have a Cyrix battery combiner that I will soon fit and then I can change the engine 1-both-2 for a simple on-off to the engine battery and the charging will take care of itself.
 
This is common and most manuals used to advise not to have switched on when starting an engine ... seems to be out of 'vogue' now and notice that any new gear I have - usually keeps going - while older drops out on pressing start button.

But a previous suggestion of capacitor is the way if you don't want to separate batterys functions. The capacity connected to the item - to supply only the item ...
 
Andrew_Trayfoot said:
So the setup is:
2 batteries: 1 110ah leasure(getting a bit tired), 1 cranking.
1,2, both switch.
Wiring is all up to or above spec.
Garmin GPS 126, FishFinder100, Matsutec HP33A AIS. All perfectly ok when starting the engine.
Owna KMR-6 drops out.

I tend to only use the engine battery to start from cold.

So the only current problem I have is the drop out of the Owna.

Might look at VSR etc next winter.
DC-DC converter and the diode/capacitor look interesting so will look at that.
Click to expand...
I think the "Getting a bit tired" may be a clue. However if all the instruments listed are supplied from the leisure battery and you are specifically using the engine start battery to start the engine. How are they connected? Or does it only happen when not starting from cold and you have both batteries or just the leisure battery in circuit?
 
Alex_Blackwood said:
I think the "Getting a bit tired" may be a clue. However if all the instruments listed are supplied from the leisure battery and you are specifically using the engine start battery to start the engine. How are they connected? Or does it only happen when not starting from cold and you have both batteries or just the leisure battery in circuit?
Click to expand...
1-2-B switch, everything runs from whichever battery is selected.

Lots of suggestions in the thread to workaround a system that wa never designed to be used with this level of equipment (was conceived decades ago, to give redundancy for engine starting, to basic systems of the day), rather than fir a dedicated battery for the engine, doubling domestic capacity in the process.
 
PaulRainbow said:
1-2-B switch, everything runs from whichever battery is selected.

Lots of suggestions in the thread to workaround a system that wa never designed to be used with this level of equipment (was conceived decades ago, to give redundancy for engine starting, to basic systems of the day), rather than fir a dedicated battery for the engine, doubling domestic capacity in the process.
Click to expand...
Fair enough Paul but 1-2- B switches I have seen select the engine start battery. I know not all the same but wondered on OP's configuration.
 
roaringgirl said:
If the voltage is dropping enough for an instrument to crap out, your battery is either nearing end of life, or you have a wiring problem and this is the first warning sign.
Click to expand...

I can only partially agree there .... I do not disagree that battery load check and wiring as well .... but ..............

My Lowrance would drop out when starting engine - then I put in a higher capacity battery with significantly higher CCA rating ... the drop was less and the Lowrance stayed on ... except when battery needed top-up charge.
I realised this when I noted that with BOTH batterys selected on my old 1-B-2-Off switch - I had selected BOTH batterys ... the combined batterys suffered less drop.
 
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