Starter voltage

[JohnSn]

Hi fellow Hunter 356 owners!
i’ve noticed that when my house battery bank is at 60% charge, it can’t start the engine. The starter bank is always up to the task and fully charged. When the house bank can’t start the engine, the battery voltage is about 11.2v during the starter runtime, and I measured the voltage at the starter motor and saw 6-7 volts. That seems low to me. There is a pretty long wire run from the batteries to the engine. Do others see voltages that low at the starter motor when it’s running? I’m trying to figure out if this is simply a typical drop for our wiring harnesses, or is it the root cause of my starting issue.
Thanks for any insights you might share!
John

 

[JoeWhite]

Let me guess that your battery and starter lugs need to be cleaned. 11.2 volt is very low volts with starter energized. You may consider replacing the battery.

 

[shemandr]

When you say "... it can't start the engine.", what happens? Does it crank the engine but too slowly to start? Or is there no cranking? A solenoid click?
You're probably familiar with the wiring harness weakness on the Yanmar (And other) engines. There is too much voltage loss in the inadequate wiring. So the starter doesn't have enough juice and you get a no start. In your case the starting battery has enough juice to overcome the weakness. With the house bank at 60% maybe not.
I am not a battery expert or engine guy, but I did have a 356 which had the problem which I fixed by putting another solenoid down line from the ignition switch. That solenoid when energized by the ignition (Takes much less voltage) would close the starter circuit which had shorter and beefier wires and had less voltage loss.
You could test the voltage loss theory by running a lower gage wire from the ignition switch to the solenoid. You wouldn't need to snake it. Then see if the house battery can start the motor at 60% discharge.

 

[Ralph Johnstone]

Do a calculation from the start using the length of wire to the starter motor (do not confuse this with the starter relay. That's a whole different story) from the battery and most important of all, the gauge of the wire. From that info, you can calculate the theoretical voltage drop and compare it to the actual voltage drop you are seeing. You DO NOT want to make a bunch of expensive alterations and finally find out you were barking up the wrong tree.

So far all you've got is "sort of, yeah abit, maybe dirty contacts, kinda pretty close" which doesn't tell you a thing which you can use.

Use these columns only for the resistance. Your wire to the starter motor should be down in the AWG #2 or lower :

 

[dlochner]

How old are your batteries? What kind of batteries, FLA, AGM, LFP? How are you estimating the SOC?

Lead acid Batteries lose capacity over time and cycles. Large drops in voltage under load are indicative of a battery that does not have the capacity for the load. SOC gauges may show 100% SOC, however, if the battery capacity has dropped to say, 80% a 100ah battery only has a capacity of 80ah and if that battery is at 60% SOC then the battery only has a capacity of 48ah. Assuming the battery connections are tight and corrosion free, your house battery does not have the capacity to deliver a high starting current, ~250a to turn the starter over.

The short story, the house bank may well need replacing.

You're probably familiar with the wiring harness weakness on the Yanmar (And other) engines. There is too much voltage loss in the inadequate wiring. So the starter doesn't have enough juice and you get a no start. In your case the starting battery has enough juice to overcome the weakness.

The Yanmar problem is not with the starter motor, it is with the wire to the solenoid from the start button. Due to corrosion and inadequately sized wire there is not enough voltage to engage the solenoid to provide current to the starter.

 

[JohnSn]

Thanks for the feedback!
The house bank is just a few weeks old. Deep Cycle, US Battery 300Ah made of 2 6 volt batteries in series. My cousin is one of the foremost experts in lead acid battery and designed them. I perhaps should say he “was”. We’ve gotten a bit older….
it’s clearly not a solenoid energizing challenge. The starter does turn over the engine slowly.
At 60% charge refers to the Victron Battery monitor counting amp hours in and out. In my quick test, the battery voltage was 11.5V when not starting. Dropped to 11.2V when starting.
it’s a good idea to calculate the wire resistance! The Victron can measure the starter current for me. Then I can calculate the expected voltage drop.
The vessel and I are on expedition. Sailing multiple days without stopping, autopilot and refrigerator loads in place, so deep discharges do happen. I’ve had her 7 years, so I pay attention when my ears tell me something changed. For the next couple of months she’s in a safe, but remote harbor near Loreto, Baja. So, I’d like to be in solid shape before leaving port again.
Thanks again for the help!
John
If anyone with a 356 is willing to measure the voltage across their starter when starting, it would be a helpful insight.

 

[Richard19068]

At 60% charge refers to the Victron Battery monitor counting amp hours in and out. In my quick test, the battery voltage was 11.5V when not starting. Dropped to 11.2V when starting.

I am certainly not an expert but isn't 11.5 volts considered nearly dead for a resting 12 volt battery bank? i.e. closer to 10 or 20 percent than 60%?
Perhaps you just need to make sure the batteries are fully charged, closer to 12.6 - 12.8 volts?

 

[JohnSn]

With a Fully charged house bank, it starts very perky. Given that the battery voltage is 11.2V in this low charge state and during starting tells me the battery has sufficient power to start the engine Even at this low state of charge.
I did the math on the wiring loss. It should amount to about 1V. The wiring in the 356 is 00 according to the manual. I guess about 60’ of wire total + and ground. And a ballpark of 250A starting current. So, 6V drop is excessive. I’ll run through and check voltage drop at each access point along the cables. The boat is 23 years old, so there may be some corrosion or loose connection.

 

[dlochner]

11.5 v seems quite low, I'm not surprised about the slow starter.

When the Victron meter was installed, did you include the Peukert factor? Without it the SOC readings are really just rough estimates.

You mentioned you were on expedition, how are you charging the batteries? At 60% SOC, it will take around 5-6 hours or more to return the batteries to 100%SOC. The longer the batteries are below 100% the greater the batteries sulfating which is what kills batteries.

 

[Ralph Johnstone]

The wiring in the 356 is 00 according to the manual.

If there's been a previous owner before yourself, this may have been altered. Eyeball the total length for gauge before trusting this figure.

 

[Richard19068]

With a Fully charged house bank, it starts very perky. Given that the battery voltage is 11.2V in this low charge state and during starting tells me the battery has sufficient power to start the engine Even at this low state of charge. I did the math on the wiring loss. It should amount to about 1V. The wiring in the 356 is 00 according to the manual. I guess about 60’ of wire total + and ground. And a ballpark of 250A starting current. So, 6V drop is excessive. I’ll run through and check voltage drop at each access point along the cables. The boat is 23 years old, so there may be some corrosion or loose connection.

So you have shown that you can start your engine with even a very undercharged battery (based on charts I have seen I think at 11.5v resting it is quite a bit less than 60% charged). Sounds good.

Again, I am not an expert, but I would suggest your batteries should be fully charged before you can do any meaningful voltage drop or load tests.

Additionally, I have read that running your starter with low voltage can damage the strarter and solenoid.

 

[JamesG161]

Get a new Start Battery, then check again. Mine cost <$100 at Wallyworld.

Jim...

 

[jssailem]

1. When the house bank can’t start the engine, the battery voltage is about 11.2v during the starter runtime, and
2. I measured the voltage at the starter motor and saw 6-7 volts. That seems low to me.
3. There is a pretty long wire run from the batteries to the engine.
4. Do others see voltages that low at the starter motor when it’s running?
5. I’m trying to figure out if this is simply a typical drop for our wiring harnesses, or is it the root cause of my starting issue.

1. Low battery voltage is a killer of starter motors. There is a whole series of component failures.

2. Measured at the Starter Motor 10.5 is usual. 9 or less can cause damage to the internal components of the starter motor. Measure the amps at the starter. 150 to 200A is usual at 12V.. As voltage drops Amps go up. High amps will burn up your starter.

3. Your long wire run and loose connections can contribute to your low voltage.

4. I do not. Short wire run of 1/0 AWG wires

5. No idea if it is typical. It maybe a factor in your described problem.

 

[JohnSn]

Thanks again for all the insights. I’m starting to get a different picture. When the house bank is low, I should just switch over and use the starter battery. If I start with the deeply discharged house bank, the voltage is too low to provide enough current to move the starter motor, so no back emf from the starter motor, so starer currents go through the roof, potentially burning out the starter, and creating bigger voltage drops to the starter motor. It all adds up. This is an operator error.
That’s why I asked!
How did the batteries get so discharged? I was sailing 1000 miles and midway the engine died (another story). I have solar, but not enough for this application. So, I was using my handy honda backup generator to try to keep the batteries from getting too far discharged. When I finally started the engine, I noticed the problem. I just wanted to make certain I don’t have a wiring problem.
Oh, both the starter bank and house bank are new.

 

[JamesG161]

When I finally started the engine, I noticed the problem.

My H430 has same set up

The engine charges the Start Battery

Jim...