Electrical Question - engine start

[karonoko]

Scotia's original Yanmar 8 works like a charm, and starts in seconds. However, when I have my VHF on stand-by (from the original panel), she won't crank. If I shut the radio off, she starts. Obviously there is a draw that is interfering with the engine start power needs.

Does anyone have a solution for this? My battery is a new one (Interstate 24M-XHD Cranking). Thanks.

[tjr818]

You say she won't crank, does she try to crank? Can you hear a click at the solenoid? How is the radio connected to 12VDC?

[karonoko]

She doesn't crank at all. There sometimes is a dull click sound. The radio is on the panel in its own circuit. The engine start is also on the panel as originally designed. With Battery selected for my engine battery, both draw from that battery. Hope that answers your good questions. Thanks.

[tjr818]

Try turning off the radio, but turn on EVERY thing else, lights, pumps, as much as you can. Then see if you get the same results. I'm guessing a bad ground connection or bad connections at the starter switch and with any additional drain on the battery there is just not enough power left to overcome the bad connection.

[karonoko]

I will give that a try. Are you thinking the solenoid is shot?

[JWSutcliffe]

Don't know how the old Yanmar wiring is arranged, but on the larger Cape Dories with Universal engines the various connections and fuse holders between the engine panel and solenoid are notorious for developing corrosion over 30 years. A few additional ohms of resistance at each connection, combined with undersized wiring, leads to insufficient voltage to actuate the starter solenoid. Best upgrade I did, in terms of eliminating the stress of wondering if the engine would crank, was to replace the whole wiring run.

[karonoko]

I went to the boat today to try your suggestions. I put the battery switch onto "engine battery - 1" and turned on all the circuits and all the lights, etc. except the VHF. She cranked right up. Not much of a draw I suppose from just a bank of lights some of which are LED. I then turned them off, and she cranked up again; but with the VHF on, no dice. My brand new ICOM GPS VHF draws at most on standby 1.5 amps (rated as such for RX).

This is a freshwater boat, and always has been, and my engine and connections have no corrosion that I can see. Interesting, I put the battery switch onto "All" so that both engine and house batteries were providing power.....no crank (I suspect the house was drawing down the engine battery a bit at the same moment?).

One suggestion below is to replace the wiring (which?), but I am open to all suggestions, and greatly appreciative.

[tjr818]

T.
The LED lights would not put enough draw on the battery to match draw of the radio. If you are certain that both batteries are good, I am stumped. I'll think this over tonight with the help of a Guinness or two and let you know what we come up with. What happens if you try to start with battery #2 alone?
Have you tried jumping the starter straight from the battery, bypassing the switch wiring?

[swhfire21]

T.

I'd identify and follow the common paths (+ & -) from batteries to both devices (radio/engine) looking for loose, cracked or corroded connections. If both are fed from same battery switch and wiring at the batteries looks good the battery switch (assuming its common) would be high on my list of suspects. Jumping out one part/connection at a time or using an ohm meter across them can help.

Bad connections can drive one crazy, it only takes an extra fraction of an amp across one to cause enough voltage drop to muck everything up.

Good luck

[karonoko]

Went back to the boat last night and traced all lines from the batteries to the battery switch/panel. Also the ground to the plate. All lines and connections appeared "like new" with no cracks, loose connections or corrosion. Now I need to inspect the connection at the engine, which as most of you know requires one to have a 90 degree neck! I am starting to conclude that this is a problem at the starter or thereabouts, and of course I am not handy with an ohm meter. Any further thoughts?

[camroll]

My guess is that your problem lies with the radio connection. The wires and connections may be good but I suspect it is wired incorrectly. There is no way a radio will have enough draw to make an engine fail to turn over especially if it starts fine otherwise. I think you may be shorting everything to ground somehow. Try hooking the radio wires up to another circuit. Make sure the wires aren't reversed on the radio. ( i.e. ground to power ) Good luck

Russ

[karonoko]

Update....
In researching this and seeing your posts (thanks) I discovered that a large voltage drop (due to engine cranking) was starving the radio of power as noted, but that this can cause serious harm to electronics. So, I installed a Blue Sea ACR (automatic charging relay) and accompanying battery switch. This switch replaces the old stalwart "1,2 or both" that came with our Cape Dories. It keeps the two batteries isolated, and the ACR joins the alternator charge to both but again keeps them isolated during discharge. It's an easy "batteries on/batteries off" switch. During the install I checked all my wiring and all looked tight and clean.

So, I still have yet to find out why such a large voltage drop during my cranking. Perhaps it's normal (and I have not measured the voltage, just assuming). She starts right up though (sometimes with 2-3 presses of the ignition button but mostly just one), and now Lady NOAA on the radio is uninterrupted, at least!

thoughts? thanks.... Tom.

[Astronomertoo]

Update....
In researching this and seeing your posts (thanks) I discovered that a large voltage drop (due to engine cranking) was starving the radio of power as noted, but that this can cause serious harm to electronics. So, I installed a Blue Sea ACR (automatic charging relay) and accompanying battery switch. This switch replaces the old stalwart "1,2 or both" that came with our Cape Dories. It keeps the two batteries isolated, and the ACR joins the alternator charge to both but again keeps them isolated during discharge. It's an easy "batteries on/batteries off" switch. During the install I checked all my wiring and all looked tight and clean.

So, I still have yet to find out why such a large voltage drop during my cranking. Perhaps it's normal (and I have not measured the voltage, just assuming). She starts right up though (sometimes with 2-3 presses of the ignition button but mostly just one), and now Lady NOAA on the radio is uninterrupted, at least!

thoughts? thanks.... Tom.

Hi Tom, all.
For normal lead acid wet batteries, I would expect the the normal voltage drop on your 12 Vdc buss would be about (or less than) 2 volts, if the batteries are reasonably charged and in good condition. If you have a battery that is not in good condition, ie, has a shorted cell, I would expect to see an additional 2 volt drop with high starting current, which would make a total of 4 volts dropped. If two bad cells, add another 2 volt drop. That could cause other loads to fail if they will not remain on, or shut off, with the the lower voltage. If you engine is starting up normally, it might be good to put a meter (preferrable a voltmeter with an analog movement meter) on the DC buss and watch to see what the lowest voltage is. You should do this test with a single 12 v battery slelected, not 2 in parallel. Regardless, a battery with bad cells will still float out at full charge, but will boil water out of any bad cells over time, and you would be adding distilled water to the lower level cells. All cells should normally remain even. If not, that is an indicator of time to test, and perhaps replace a battery. And, NEVER add water to a discharged battery as the water will overflow with charging! Makes a mess! Charge first, then add water.
Bob C