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House batteries won't start engine - ideas?

3899 Views 24 Replies 15 Participants Last post by  findrichard
I would love any suggestions about how to tackle this question -- my sailboat has a 3 batteries and a standard off/1/both/2 Perko switch. Battery 1 is used as the starting battery, even though it is a deep cycle (It was on the boat that way when I bought it). Battery 2 is actually 2 deep cycles (group 27, 830 mca), almost brand new, in parallel. They run the lights, etc fine, but when I turn the switch to battery 2, the starter switch will buzz, but then it will not provide enough juice (it does some, just not enough) to actually start my engine (an old 30 hp diesel). I don't do that except to test that #2 will actually start the engine in case #1 fails, which has not happened lately, so this is not an emergency situation, but I cannot figure out what may be happening. Shouldn't my deep cycles be enough to start the engine? I have considered a wiring problem, but am not an expert and can't logically figure out why, if everything else runs ok on #2, why the engine won't start on it?? Anyone have any ideas of what I should be checking? Is it possible that a loose connection or something means enough power is getting out to handle the lights etc but not the engine? Thank you very much, and I won't be offended if anyone thinks I am misunderstanding basics or missing an obvious issue!
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Check the voltage, then start cleaning every connection from the batteries to the starter. Start at the batteries, then the starter, then everything in between. It could also be a bad solenoid on the starter.
First check all the terminals for corrosion. If that is good and the batts are not sealed buy a battery tester. Do you have a volt or amp meter you can interpret after the engine is running to gauge the battery condition. Search for "Maine Sail" electrical blogs on this site or "Compass Marine". Good luck.:)
what cranking amps is the starter battery or battery bank 1?

the big difference bewteen deep cycle batteries and starter batteries are cranking amps

having said that I became an expert on starting my yanmar 2gm on very VERY low batteries using the decomp levers...

once my deep cycle house bank got below a certain level, even though they were in parallel it made no difference if it was 1, 2 or 4 batteries

a good high cranking amp starter battery(I love truck batteries) is very useful to have singled out for just that

starter batteries are thought of as sprinters where deep cycle are thought of as marathon runners

but it could absolutely be a wiring issue or even a starter motor issue which sounds more plausible to me

is it in good condition? has it ever been rebuilt? contacts and brushes good?

x2 on comments above, start simple...
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Thanks for replying, I appreciate it. I have cleaned the connections on the battery end of things, I haven't otherwise yet. If there were a problem with the starter itself, though, wouldn't that affect starting when on battery #1 also? Or (and sorry if I should know this) are there normally separate wires out of the Perko switch to the starter for #1 and #2 (I didn't think so but maybe). In any case, thanks again
Thanks for replying, I appreciate it. I have cleaned the connections on the battery end of things, I haven't otherwise yet. If there were a problem with the starter itself, though, wouldn't that affect starting when on battery #1 also? Or (and sorry if I should know this) are there normally separate wires out of the Perko switch to the starter for #1 and #2 (I didn't think so but maybe). In any case, thanks again
yes it would hence why I asked what cranking amps your starter battery is or size?

for all you know the starter battery might have more power than the 2 combined deep cycles..

it could also be simply that you have bad NEW batteries

it can also be your switch is faulty:) check voltage at switch
If the solenoid chatters it means the battery is low. If there is nothing run a wire from the battery straight to the post that actuates the solenoid. Your starter could be engaged. This will tell you if your switch to turn over the engine is not operating. If nothing happens is your ground to the starter loose? Do not go straight from the battery to the post that connects the battery to the starter. A lot of current is drawn by the starter. Yes clean all your connections as stated in the previous post. I just replaced my starter and it did not start the engine. Took it back out and had it tested. It worked. I am in the process of replacing the starter and broke the frayed wire going to the start button. Electricity is fun!!

Dot and John
Thank you again for the replies. I will have to check the cranking amps on battery #1, but I would be surprised if they were lower than on #2. I will do a thorough check and cleaning, and see what that fixes. i guess i am still hung up on why it starts fine on #1 and not #2 -- assuming batter(ies) #2 are good, which I will confirm. Thank you again.
im implying it might be higher than bank 2 could be low voltage and not charged properly, or a bad set even if new

if your switch is faulty on number 2 you might not be charging properly and it will be lower voltage than bank number number 1 may be a better quality higher amp...

it sounds like there is a problem with bank number 2...thats all.

let us know!

good luck
There should not be a problem starting with 2 group 27 batteries if they are in good condition - regardless of their cranking amps.

Since the engine starts fine with the single starter battery the starter is fine.

Clean all connections from the house bank to the Perko battery switch and make sure they are tight. Don't forget the interconnects between the 2 batteries.

Do you have a digital multimeter? If not get one, $15 or less.

Measure the voltage at the posts of the house bank. Then measure it again while trying to crank the engine.

It's possible that there is a bad connection between the house batteries and the Perko switch. We know the wiring is good after the switch as the other battery starts the engine. It could be that the house batteries can run lights etc but do not have enough capacity to start the engine.
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im betting a switch issue or bad batteries...or improperly charged batteries due to any of the above suggestions...

contact cleaner is great for switches in general
Switch the banks, then you'll know if it's batteries or wiring.
Battery 2 is actually 2 deep cycles (group 27, 830 mca), almost brand new, in parallel.
You have over 1600 cranking amps at 32F! At 70F you are well beyond 2000 cranking amps! Your motor needs about 250A - 300A +/- for less than 0.2 seconds then about 150A for another couple of seconds. ANY deep cycle battery on the planet can EASILY start a small marine AUX diesel.

If these batteries are "almost brand new" then you have system wiring issue such as bad terminations, bad ground, bad switch, dirty ground, etc. etc.... Your house bank should start your motor far better than your single starting battery even at 50% SOC....

Easiest test to determine a wiring issue is flip flop the bank positive wiring.. If the other battery does the same on the #2 circuit start chasing wiring issues...
I went through this recently on my boat.

Fundamentally the problem is likely to be a high resistance connection somewhere, because it's loose or corroded. At starting currents, even a fraction of an ohm is significant. It's quite possible to have a resistive contact that does not cause much loss at normal house bank currents (I never go over 20A), but when you start pulling 300A you lose several volts at the bad connection.

A starter needs ideally 9V, and the battery voltage might drop to 11V while starting, so that means no more than 2V drop across all your cables and the battery switch. All the connections need to be in tip-top state to achieve this.

There is no substitute for a careful measurement of voltage drops between the starter and the batteries, WHILE engaging the starter.

My main issue was a loose nut on a connection at the starter. However, I also replaced several poorly-made battery cables, and the Perko switch itself. The Blue Sea Systems switches are better. I got the battery cables from, and went a size larger.

It REALLY starts nicely now!
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My yanmar 2gm is often hard to start after it has sat for many weeks even if I put the batteries in parallel to double the current. I think this is because the 2gm is not the original engine (Original was a 1gm)and my batteries may be too small and because the lubricating oil film on the inside of the cylinders has gone away after sitting awhile. So, after sitting for a few weeks, I always relieve the compression first before cranking to allow it to get a good oil film and then I drop the compression in and crank again. Always seems to work. Any corrosion on terminals is bad when your batteries are iffy.
Years ago, I stopped for someone in a parking lot with their hood up and jumper cables connected. I popped my hood; they hooked up their cables.

Their lights got noticeably brighter, but the engine wouldn't turn over.

They had El Cheapo jumper cables. I got out my set and had them running in 30 seconds.

Two lessons:
1. Always have your own gear that you can trust.

2. 12VDC 0.25A is very different from 12VDC 100A.

Their set had poor clamps and undersized cable. I suspect something similar on your boat. If you can, run jumper cables from House right to your starter*; if that cranks like mad it is your connections and/or cables. If not, it is your batteries.

Are the cables for House the same size as Engine?

Are they (a lot) longer?


*You'll want to be careful.
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^^^good very good points
One thing I found rather useful was a couple of 6 ft leads for the multi-meter, that I made. Large crocodile clips on one end, banana plugs on the other. The standard leads that come with the meter are nowhere near long enough.
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dude! I keep wanting to do that as I drop the multimeter ALL the time when testing stuff as the leads are just so damn short!


I see im not the only one
Thank you all for your assessments and suggestions, I will follow them and I will report back soon with anything useful for the community I have learned. Thanks again
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