engine start battery voltage drops below 10v when starting engine

[lw395]

I'm in the other camp and consider the 1-2-both switch is the pinnacle of simplicity, but not understood by 95% of the people who use them.

It works for a lot of people. To be fair, it's a product of the 70s, and a lot has moved on.

Other systems need some sort of VSr or charge splitter or B>B charger. Whichever is fashionable this week.
Your comment "not understood by 95% of the people who use them" could equally apply.

 

[GHA]

So, I'd be checking the wiring etc before exercising my credit card.

In general very good advice - even if it does look like the battery. For boat problems when you're sure of the source of the problem a good mantra is imho "But I might be wrong, better check .."

 

[PaulRainbow]

I have your set up on one boat and the 0-1-2-Both switch on the other. Both work perfectly well, although the rotary switch is more flexible in how I want to use the batteries. On the first boat we have guests often and some like to take part in the sailing and motoring and the domestic bank is far bigger than the engine start so I prefer the much safer and easier option. On the other it's usually just me on board and with identical engine start and domestic battery so like the flexibility.

How do you feel the 1-2-both is more flexible Rupert ?

 

[JumbleDuck]

How do you feel the 1-2-both is more flexible Rupert ?

It allows either battery to be used on its own for any purpose. I have separate domestic and engine circuits with a link between them when needed, but that doesn't on its own allow either battery to be disconnected completely. I have added thermal cutouts to each battery which I can pop if required, but it's less handy than with a 1-2-both.

On the other hand, how often would I actually want to do that?

 

[[70521]]

I also have a routine, turn switch on, use boat, turn switch off, leave boat. My batteries are always charged, no chance of running the engine battery flat, no user intervention required. Simple.

What could be simpler than two switches, one for the engine battery and one for the domestics ? Arrive at boat, turn domestics on. Want to use the engine, turn it on, finished with it, turn it off or leave it on until you leave, doesn't matter either way. Throw in a third for emergency use and you're laughing.

What a complicated way of doing things, but "hey ho" there are 101 different was to skin a cat. As long as you are happy to do what you do on your boat and I'm happy to do what I am doing on mine then happy daze....

 

[RupertW]

It allows either battery to be used on its own for any purpose. I have separate domestic and engine circuits with a link between them when needed, but that doesn't on its own allow either battery to be disconnected completely. I have added thermal cutouts to each battery which I can pop if required, but it's less handy than with a 1-2-both.

On the other hand, how often would I actually want to do that?

I use them interchangeably - budget sailing really where I don't mind one battery being nearer the end of it's life instead of making sure all batteries are healthy (as I do on the other boat). So if one battery has a low voltage I might decide to use it to start the engine and leave it on engine to charge up without using the other battery at all. It allows me to think of batteries as being 2 separate assets without an "engine" or "domestic" label. That way would lie madness if more than one person involved, and make no sense in a bigger seteup with different sized banks.

 

[PaulRainbow]

It allows either battery to be used on its own for any purpose. I have separate domestic and engine circuits with a link between them when needed, but that doesn't on its own allow either battery to be disconnected completely. I have added thermal cutouts to each battery which I can pop if required, but it's less handy than with a 1-2-both.

On the other hand, how often would I actually want to do that?

I also have separate switches for engine and domestic circuits, with a third providing the emergency link. My emergency switch is connected to the isolator load terminals. Normally i just turn the two switches on and leave the emergency switch off, obviously. If the engine battery were a little flat i'd turn on the emergency switch, start the engine and turn it off again. In the event of a catastrophic battery failure i can completely isolate the failed battery by turning its switch off and run everything from the other bank by turning the emergency switch on.

 

[PaulRainbow]

What a complicated way of doing things, but "hey ho" there are 101 different was to skin a cat. As long as you are happy to do what you do on your boat and I'm happy to do what I am doing on mine then happy daze....

I fail to see how turning a switch on is complicated Sandy. Perhaps you fall into the "not understood by 95% of the people who don't use them" camp

As you say though, if you're happy.................

 

[ieb]

Had a similar problems in 2 boats.
Boat 1, a Davidson 34 with small Bukh Engine (probably 1KW starter) had a 1-2 both switch which turned out to have slightly dirty contacts internally only impacting engine start and only when batteries were a few years old. New switch fixed that. I think the internal springs on the switch might have gone. The contact points are not very big.

Second time, different boat, HR38, bigger engine, individual 1000A main switches, with a 2kw starter. Dedicated 990CCA engine start battery. 50A draw on glow plugs, the leads were 70mm2 but a bit long (3m), and the terminals might have been internally corroded. Moving the battery close to engine (1m) fixed it. Before fixing, on start voltages went to below 10V at the engine feed, and peaked at 250A for a few milliseconds (I put a scope on various points to work out where the trouble was, and measured the peak current with a clamp on DC hall effect meter). After fixing, I don't see anything below 10.5 even for the first start of the year. Engine always starts within 1/2s of turning the key now.
In both cases the batteries were probably replaced too soon. It was the wiring and/or connectors. Still have the battery from the second boat.

Clamp on multimeters with peak capture functions are widely available. Search YouTube for "testing a car battery start" for some examples. Hope that helps.

BTW, dead batteries voltages take a lot longer to recover from high load than good batteries, and can present a fire risk when charging @> 20A if the base of the plates has been shorted by debris.

 

[GHA]

Had a similar problems in 2 boats. ......

Welcome to the forums ieb!

And great post with far more data & actual real world measurements than most, plus how the data was measured, some opinions here are formed with no more research the crossing of legs on the sofa, refreshing.

 

[webcraft]

.
An update . . .

Checked and tightened battery terminals, no difference. Checked voltage at battery terminals with a multimeter - 12.6/12.7 volts. Battery is 45Ah, 400CCA and is kept fully charged because the boat is on a mooring and there is a wind generator.

Using the domestic batteries (2x110Ah) the voltage drops to 12 or just below 12 when starting the engine.
I experimented turning the switch to 1 and started the Webasto - started OK, but as it went through its start-up routine the voltage steadily dropped to 10 then below.

My conclusion - battery is most likely gubbed, though I don't know why - 4 years old and has had very light use, always kept charged by the wind generator. How much point is there in taking the 1-2-both switch apart? It was apart 4 years ago when the new engine battery was fitted. Presumably if it is a mysterious fault further down the line then it will show up immediately with a new engine start battery, which is only going to cost me £54 delivered anyway.

- W

 

[[70521]]

.
An update . . .

Checked and tightened battery terminals, no difference. Checked voltage at battery terminals with a multimeter - 12.6/12.7 volts. Battery is 45Ah, 400CCA and is kept fully charged because the boat is on a mooring and there is a wind generator.

Using the domestic batteries (2x110Ah) the voltage drops to 12 or just below 12 when starting the engine.
I experimented turning the switch to 1 and started the Webasto - started OK, but as it went through its start-up routine the voltage steadily dropped to 10 then below.

My conclusion - battery is most likely gubbed, though I don't know why - 4 years old and has had very light use, always kept charged by the wind generator. How much point is there in taking the 1-2-both switch apart? It was apart 4 years ago when the new engine battery was fitted. Presumably if it is a mysterious fault further down the line then it will show up immediately with a new engine start battery, which is only going to cost me £54 delivered anyway.

- W

Webby

How long does the battery take to charge? How long does it keep to charge? If it keeps its charge then you don't have a battery problem , just a voltage dip starting the engine, which is expected.

 

[ieb]

.
An update . . .

Checked and tightened battery terminals, no difference. Checked voltage at battery terminals with a multimeter - 12.6/12.7 volts. Battery is 45Ah, 400CCA and is kept fully charged because the boat is on a mooring and there is a wind generator.

Using the domestic batteries (2x110Ah) the voltage drops to 12 or just below 12 when starting the engine.
I experimented turning the switch to 1 and started the Webasto - started OK, but as it went through its start-up routine the voltage steadily dropped to 10 then below.

My conclusion - battery is most likely gubbed, though I don't know why - 4 years old and has had very light use, always kept charged by the wind generator. How much point is there in taking the 1-2-both switch apart? It was apart 4 years ago when the new engine battery was fitted. Presumably if it is a mysterious fault further down the line then it will show up immediately with a new engine start battery, which is only going to cost me £54 delivered anyway.

- W

Engine start batteries should last > 4 years if treated carefully, but that means charging it perfectly with a smart controller for the wind generator or a mains fit and forget smart charger. ie 14.4v then 13.6v float with with a reassessment by the charger every few days. For the plates to avoid degrading the wind generator needs to hold the voltage at 13.6v most of the time. Smart charge controllers are available for wind generators, but they are $$ even on eBay... and dont work when there is no wind.... but when there is will charge the battery as best they can. Solar MPPT controllers dont work for wind generators. There is a rant by the founder of Sterling Power on the battery charging, somewhere on the internet. Google will probably find it. Worth reading.

Sounds like your switch and wiring is ok since the domestic pair started the engine Ok. You could confirm no fault on the engine battery wiring and switch by swapping the domestic batteries with the engine battery and starting on that side of the switch.

A cheap car battery tester will also verify if the start battery is dead.

Hope that helps.



I

 

[RichardS]

Sounds like your switch and wiring is ok since the domestic pair started the engine Ok. You could confirm no fault on the engine battery wiring and switch by swapping the domestic batteries with the engine battery and starting on that side of the switch.

Or just use/borrow some auto jump leads to bypass all the wiring and switches. I carry a pair of 5m heavy duty jump leads on the boat just for this kind of eventuality. I've only used them once in earnest in 3 years but they're cheap enough on eBay.

Richard

 

[macd]

If it keeps its charge then you don't have a battery problem , just a voltage dip starting the engine, which is expected.

The "voltage dip" is when the battery fails to start the engine.
However, it evidently has more than enough power to start a groundhog every day.

 

[superheat6k]

Rather a pointles dig, considering that the vast majority of "British" batteriies are badge -engineered and made in China! But heigh- ho, if it makes you feel good-----

Yes it was a cheap shot, but I presume you do not visit the lounge to observe Webby's rants against RUK. Please read the whole sentence.

 

[webcraft]

Webby

How long does the battery take to charge? How long does it keep to charge? If it keeps its charge then you don't have a battery problem , just a voltage dip starting the engine, which is expected.

The battery always seems to be fully charged (12.65 volts or thereabouts) (from the wind genny). It used to start the engine no bother with no voltage drop - or not sufficient to kill the VHF etc - so something has changed.

- W

 

[VicS]

The battery always seems to be fully charged (12.65 volts or thereabouts) (from the wind genny). It used to start the engine no bother with no voltage drop - or not sufficient to kill the VHF etc - so something has changed.

- W

It depends how and when you are measuring 12.65 V . If it is when the battery has rested with no load and no charge for at least 12 hours its not bad but somewhat short of fully charged. I would try further charging to see if the rested volts can be increased to at least 12.7.

You then need to monitor the battery with no load and no further charge for as long as possible. Although the volts will fall more quickly at first the rate of fall should decrease so that it takes several weeks or more to fall to around 12.5 V.

If you can get it up 12.7 and if if keeps its charge well it has a chance but these observations do not guarantee that it can supply the current necessary to crank the engine properly. You could have it tested at this point or simply try it!

If however you are measuring 12.65 volts while it is being charged it is not very meaningful but I'd not be optimistic about it.

 

[PaulRainbow]

The battery always seems to be fully charged (12.65 volts or thereabouts) (from the wind genny). It used to start the engine no bother with no voltage drop - or not sufficient to kill the VHF etc - so something has changed.

- W

Something has, the battery has died.

 

[alahol2]

Had a similarly dying battery at the end of last year. I could get it charged up to 12.7 V or so and it would hold it for ages. I found the only way to really test the battery was to do a rough capacity test. Charge up fully. Put a load on it (in my case about 4A) and see how long it takes to get down to 10.5V. My nominally 110Ah battery ended up giving (very) roughly 50Ah. That was enough to convince me.