Engine Starting Battery

[mcrow33]

Hi all,

I have a question about engine starting and batteries. First my Endeavour has a Yanmar 2QM20H. I have two marine batteries connected to a selector switch. My plan was to use battery one as the starting battery and battery two as the house battery. That way I don't run the starting battery down with lights and stuff. Both batteries were charged and the charger showed 100% charge. The test switch shows both batteries as fully charged. Here is the issue or possible issue. When trying to start the engine, I need to have the selector switch on both for the engine to turn over fast enough to start the engine. Just one battery won't work. Is this normal? Is my battery not strong enough? I am planning on testing each cell with an tester, to be sure I don't have a dead cell, but I thought I would post the question, to see if I really need to use both batteries to turn this engine over.

Thanks,
Mike

 

[Benny17441]

One or both of the batteries could be weak but a more likely scenario is that you have a loose or corroded connection between batteries and engine ground or starter. The 2gm should start easily with just one battery. There is no need to have a dedicated engine starter battery. What a lot of folks do is two set up two deep cycle batteries which could be used as house batteries as well as starting the engine. I prefer to alternate them so that both get approximately the same amount of usage and I always use one at a time to keep the second in reserve. For example battery #1 would be used for starting the engine and running refrigeration. While motoring out that battery would be receiving the full alternator charge. When cutting the engine out it would continue providing power to the refrigerator and the instruments. After 3 hours or so that battery will still have power to cranck the engine but should it be slow and can switch to both. The following outing I will switch to battery #2. If anchoring out I will continue to use the chosen battery but will control the loads. That may entail manually cycling the refrigerator on and off. In our case we pack a honda eu2000 generator so we recharge the battery at anchor. Another option we have utilized is to carry a third fully charged battery and then we can use both deep cycle batteries as house batteries and still have assured power to start the engine. Chcek your current connections and the voltage drop when you hit the starter button. You may also test the resistance in wires themselves.

 

[KD3PC]

One good, charged battery should do the job, un assisted....something is up...I would check the battery with a "load tester" and if it shows good, start looking at connections to and from the battery and engine, starter, etc.

 

[Eric M]

You don't mention what size batteries you have so hard to say for certain but most single batteries should start that motor. I have a Yanmar 3GM that starts off a single 105Ah battery. Your plan is sound to have seperate starting and house batteries. Sounds like you are heading in the right direction to check out each battery with a load tester. If you find both batteries to be weak, but not yet dead, you could consider combining them into a pair as your house bank and purchase a new starting battery.
Good Luck

 

[Stu Jackson]

How old are the batteries? Good advice here to check the connections. Most folks find the "weak link" is the ground connection at the engine.

You might find some of the material here interesting: Electrical Systems 101 --- http://c34.org/bbs/index.php/topic,5977.0.html

 

[mcrow33]

So, if I need to replace the battery. Should I replace it with another marine deep cycle, or a standard starting battery. Knowing that I will only be using this battery for starting and not as a house battery. I also should note that the house battery, will be only running lights, and few instruments. As for the age, I'm not sure. I just bought the boat.

 

[Don S/V ILLusion]

There is no wrong answer to your question regarding using a deep cycle or start battery. Either will suffice for your purpose as you don't need a large house bank capacity. The advantage of having two deep cycle batteries is that they are interchangeable if need be; not true if you have one of each type. More flexibility is usually better.

 

[Stu Jackson]

Don's point is well taken. Those of us with larger house loads use a larger house bank and a smaller reserve (backup) battery, just in case. We start our engines with the deep cycle house bank, the reserve bank is usually a simple automotive "start" battery.

For those, like you, with a tiny house load, you may want to consider "reverting" to the "olden days" dual house bank approach: two equal batteries, use one one day, the other the next. The advantage here for you is that you are essentially doubling your house bank capacity, assuming you charge some each day.

The reasons this fell out of favor are: electrical loads began to climb on boats in the past decade or two (the largest load is usually a fridge), requiring greater house bank capacity; battery technology and research showed that the very same amount of lead (batteries) lasted longer with less % draw down based on the identical daily load, since the same load was a smaller % of a combined larger bank than two separate ones.

Since you have such meager loads, why not consider it? At least for now, since you will undoubtedly add stuff as you learn more about your new boat.

Congrats on your new boat, nice boat, was the first "big" boat we ever did a bareboat on in the Virgin Islands.

 

[Deadline]

As for replacing...

Stu- If in fact one battery needs replacing, you should do both as that's the protocol. I tell people that batteries are like politicians. Not very reliable and have to be replaced every two years.

 

[Don S/V ILLusion]

While the generality is true (replace all batteries concurrently), like any generality, there are exceptions, this being one. As Mike said he is using them independently of each other, therefore the age difference is irrelevant. Had he planned to combine them into one bank, their comparative capacity difference (i.e., age) would be an issue.

 

[Stu Jackson]

Batteries should last more than two years, how about a senate seat???

Since the batteries, as discussed, are not going to be used together, there's no reason, other than age and suspicion, that he can't do one at a time. F'rinstance, I have a separate start battery which was not replaced when I replaced my house banks.

If it was my boat...and in his situation, I'd do both.

 

[kenn]

I'm betting the problem is either a connection issue of some type as already mentioned... or that the present battery wiring is simply inadequate.

On a power-boat I worked on last year, the owner had put two BIG batteries in paralled for starting, but still had poor cranking. I measured a drop of 5 to 6 v from the starting battery's +ve terminal to the starter, when cranking. I rewired the batteries with a bigger cable gauge and relocated the battery switch closer to the batteries, and now the engine cranks briskly with just one of the batteries.

 

[MitchM]

first thing i'd do is clean and dielectric grease all the contacts into your yanmar cockpit B panel key switch controlling the engine start. on the old yans this long wiring harness up into the cockpit will corrode on the back of the switch panel. then there is then a big voltage drop from start battery into the key switch panel, then back down to the starter solenoid. take a voltmeter, measure the volts across engine start battery, then measure how many volts you g et into into the key switch , then how many volts mout of the key switch back down into the starter solenoid. what counts is t he volts you are actually getting at t he s tarter solenoid, not the volts you ahve in your engine start battery. . on my old 2GM20F after 20 years i had a huge voltage drop along t he ahrness from the start battery into the b panel key switch. cleaning , dielectricing and weather proofing the back of the key switch panel was fix #1. cleaning the grounds for the batteries was fix #2. fix #3 was wiring in a direct heavy duty momentary press - on start switch, wired between the starter battery and the starter solenoid. this extra start switch thus bypassed the long wiring into the start key in the cockpit... eliminating the voltage drop. the new momentary start switch is handy if your battery gets low, as there is minimal voltage drop in this momentary switch system. the new switch also came in very handy when i was trying to start the engine from within the engine compartment to test various things, instead of having to climb into the cockpit to acces the key switch.......

of course who ever knows about it could steal your boat !

 

[rardiH36]

I also have a 2QM20. Just to indicate that something besides the batteries might be up with your slow cranking, my back-up emergency starting battery is a very small AGM that I took from our 2001 Toyota Prius when I put a new one in the car. This old/small battery cranks the 2QM20 a bit slow compared to the much larger dual-duty marine batteries I have, but it does start it.

As per the previous posts, clean connections everywhere are a must. Also if the main battery cables are old (as mine were when I bought my boat), particularly if they do not have marine grade tinned strands, then the cable itself may have diminished current carrying capacity due oxidation between the strands and the lugs/terminals.

Another item if the starter is still sluggish after you've followed the already posted suggestions, and if you have the tools/background/manual to tackle, is to remove and dismantle the starter itself. Unless a PO has done a refurb job somewhere along the line, the starter might be untouched for 30 years. Mine (which I believe was the original) had quite a bit of gunk and grease between the copper commutator and the brushes when I took it apart a couple of years ago. After cleaning off the gunk and then sanding the commutator's copper with #600 sandpaper (and per the factory manual), when I put the starter back on the engine, it did seem to have more pop than before.

 

[BobM]

http://forums.sbo.sailboatowners.com/showthread.php?p=787574&highlight=yanmar starting problem thread I was thinking about.

 

[Maine Sail]

When I got back from my sail today I plugged my Fluke 376 into my 12V panel feed and measured the max voltage dip that occurs when I start our engine.

The Fluke 376 was set to capture and hold the lowest recorded voltage and it captures these peaks or dips at 100ms or 1/10th of a second

The first video is the engine starting off the house bank at 78% state of charge. The house bank is three group 31 batteries in parallel.

The voltage bottom or dip is 11.7 V which is nowhere near low enough to drop out any electronics.

The second video is of the same engine starting on the single group 27 starting battery. This battery was at 100% state of charge. The voltage dips to just 10.3 volts which could potentially drop some older electronics out during starting.

It is clearly evident how much easier it is for the deep cycle house bank to start this 44HP four cylinder motor and hardly even feel it, despite it being a deep cycle bank.

This is a 1.4 volt difference in the "dip" the starter and electronics would see! The house bank was also down 22% and the starting bank was at 100% state of charge.

As you can see there is no real need to start a small diesel aux off the "starter" battery then switch back to the house bank as sooooooo many boaters do needlessly and risk frying alternator diodes...

The banks are five years old and have been charged via solar, a combiner and a dumb regulated 50A stock Mitsubishi alternator. The cables also help this motor jump to life. They are all 2/0...

Hope this helps put it in perspective.

 

[LloydB]

"That way I don't run the starting battery down with lights and stuff. Both batteries were charged and the charger showed 100% charge. The test switch shows both batteries as fully charged."
Is that each or together?