Knackered battery

[pessimist]

Our engine start battery appears to have shuffled off this mortal coil. Reading ~3v - it was o.k. last week. I can combine this with the house bank to start the engine but, if it has failed completely, will this cause alternator damage?

 

[Alan S]

I would disconnect it completely and use the combining switch if thats what you have so the alternator always sees a good battery.

 

[Robin]

why not replace the dead engine battery with a good quality car one, it has no need to be deep cycle, though you could go for a 'leisure' one with decent cranking amp capacity , you could also get rid of the 1/2/both and fit a proper split charge diode system. do you have twin engines on the cat?

 

[pessimist]

I would disconnect it completely and use the combining switch if thats what you have so the alternator always sees a good battery.

Thanks, but the combination switch pairs with LiFePO4 batteries so strictly temporary.

 

[pessimist]

why not replace the dead engine battery with a good quality car one, it has no need to be deep cycle, though you could go for a 'leisure' one with decent cranking amp capacity , you could also get rid of the 1/2/both and fit a proper split charge diode system. do you have twin engines on the cat?

New battery on order, just looking for an immediate fix.

 

[Alan S]

Thanks, but the combination switch pairs with LiFePO4 batteries so strictly temporary.

I thought it was clear tjat I meant as a temporary measure until you get a new start battery. Just be careful that you don't run the engine for too long and overcharge the lithium or overheat the alternator.

 

[Daydream believer]

I thought it was clear tjat I meant as a temporary measure until you get a new start battery. Just be careful that you don't run the engine for too long and overcharge the lithium or overheat the alternator.

That sounds a bit odd- you cannot go anywhere because you have lithium batteries and they must not be overcharged. Surely the system should be designed to allow the engine to run as long as one likes. Once the starter battery is full it should switch to domestics and keep charging. The fact that now there is no starter just means it switches straight to domestic

 

[Alan S]

Normal setup with lithium is that it is charged via a battery to battery charger from the lead acid staster which in turn is charged directly from th alternator. The b2b prevents excess current overloading the alternator and overcharging the lithium. If the starter battery is removed and the combining swifch is on then you don't have that protection. OK as a temporary measure.

 

[PaulRainbow]

New battery on order, just looking for an immediate fix.

If you leave the faulty engine battery connected and it has a shorted cell it won't end well.

If you completely remove it you risk overheating the alternator.

Without knowing more about your system the only safe solution i can think of is to remove the engine battery completely and replace it with one of the domestic bank.

Your Lithium system sounds poor if you are relying on a 1-2-B switch. What fuses are you using ?

 

[pessimist]

If you leave the faulty engine battery connected and it has a shorted cell it won't end well.

Thanks - that's what I was afraid of.

Using B2B/solar to charge the lithium. Class T fuse. Not a 1-2-B but emergency combination - strictly temporary for starting purposes only according to electrician who installed the system.

 

[littledancersadhu]

I have this every couple of years, just last week my big battery would only register 7 volts.
All ready taken down the scrapyard,and will refit a new next season.

1 faulty battery will pull down and flatten the good one when rotary switch is left on "BOTH".

 

[Daydream believer]

Rotary switches are a curse

 

[PaulRainbow]

If you leave the faulty engine battery connected and it has a shorted cell it won't end well.

Thanks - that's what I was afraid of.

Using B2B/solar to charge the lithium. Class T fuse. Not a 1-2-B but emergency combination - strictly temporary for starting purposes only according to electrician who installed the system.

Safe emergency options ;

1) Remove the engine battery completely and replace it with one of the domestic bank.
2) Start with the emergency switch and carefully monitor the engine battery.
3) Depending on the engine, disconnect the alternator, start the engine, turn the emergency switch off.

 

[pessimist]

Thanks everyone. New battery arriving Wednesday. Think I'll take the safe option and wait.

 

[Robin]

New battery on order, just looking for an immediate fiSorry Colin I only look in rarely and missed the previous info are you enjoying two half boats ,is it your battery knackered or pragmatists or a single shared engine?

 

[littledancersadhu]

Rotary switches are a curse

The rotary switch was all ready there when i got given the sailboat.All ways faired me well, i was told to keep away from the diode 2 battery charger units,What has been your issues with them?

 

[Daydream believer]

The rotary switch was all ready there when i got given the sailboat.All ways faired me well, i was told to keep away from the diode 2 battery charger units,What has been your issues with them?

Our club committe boat had one and different people used to leave them in the wrong position . As a result one would go to use the boat and the batteries would be flat.
My boat has a dedicated switch for starter, domestic and a different coloured one for both slightly separate from the other 2 it is easy just look at them and see which is on and which is off. Furthermore ther is no leakage across the switches which was suspected of the club switch due to damp. No idea if that was just a false assumption or not

 

[vyv_cox]

Our club committe boat had one and different people used to leave them in the wrong position . As a result one would go to use the boat and the batteries would be flat.

That's like blaming a car for crashing into pedestrians. The fault is with the operator.

There is nothing wrong with rotary switches (1-2-both) I have been using them for 45 years and never once had a flat battery due to misuse.

 

[Daydream believer]

That's like blaming a car for crashing into pedestrians. The fault is with the operator.

There is nothing wrong with rotary switches (1-2-both) I have been using them for 45 years and never once had a flat battery due to misuse.

Fair comment. But you are supper special. Not everyone remembers what way to turn the thing or to turn it back etc during use. Its design leaves it open to mistake and that is the point.
But if you like it then ok keep it. I expressed an opinion. Others can decide

 

[littledancersadhu]

I am guilty of forgetting to switch the rotary to off before i leave the boat on the rare occasion, usually it's the mobile we left ON the the boat !