Crank battery ?

[frankS]

Hi all. I just bought another boat to take down to Bermagui and leave there so I don't have to drag a boat all the way down when I want to go.

Anyhow a question. It has a deep cycle battery in it as a crank battery for the motor. Is this OK or would I have to buy a dedicated crank battery for the motor ?.

Frank

Edited July 22, 2023 by frankS

[frankS]

Think I will just bight the bullett and go and buy new crank battery and use this one for the electronics.

Plenty of room in the boat for 2nd battery.

Frank

[zmk1962]

Hi Frank, sorry mate was a busy day.

A deep cycle is designed to provide low current over a long time and survive being discharged 80-100% ie to flat ... whereas a starter battery is designed to deliver a lot of current over a short period (crank) but never get to full discharge ie. if you want longevity you should never discharge them below 50% and try and keep them in the 10-20% discharge range. 

So it's one of those it depends situation - depends on what specific deep cycle battery you have (how many Amps can it deliver instantly), and what specific motor you have (how many Amps it needs in the 2-15sec crank window). Smaller motors require less instantaneous power obviously. Also, charging the battery goes the other way - deep cycles generally take longer to charge - so what does the motor put out charging wise?

So it could be ok.

Have you got specifics of the battery or a photo. Same for motor?

In case you are interested, this is a very basic description of the principles involved, assuming they are lead acid batteries:

• Drawing power from a battery - the lead metal plates are dissolving into the acid and as part of that reaction they are releasing electricity (electrons).
• Charging a battery - you pumping electricity into the battery and forcing the metal back out of the acid onto the plates.
• Issues:  the metal does not go back evenly ... it sort of attaches itself where ever it can ... in a sort of spongey mass. Which is why the more you discharge a battery the more spongey mass is created until eventually the mass from two plates touches and shorts them out ... no more 12v.  

The Crank batteries have more thinner plates - which means there is more metal surface contact with the acid allowing for a bigger chemical reaction as more metal dissolves into the acid - which is the source of greater crank electrical power. Deep cycle have fewer thicker plates further apart - so less surface to react - less instantaneous power - but will provide a longer run time as there is more space between the plates and more metal on the plates.

Cheers Zoran

 

[XD351]

Are you going offshore in this boat Frank? If yes I would run two batteries as a safety precaution, even a deep cycle can be pressed into service to assist a crook start battery in an emergency .

[frankS]

Zoran. Thanks for the info mate . You explain it well and I have learnt yet another thing that will no doubt help along the way.

New battery on the drawing board ( tomorrow ) . I have to re-wire this boat from start to finish so might as well start with new everything including battery.

Frank

[frankS]

2 hours ago, XD351 said:

Are you going offshore in this boat Frank? If yes I would run two batteries as a safety precaution, even a deep cycle can be pressed into service to assist a crook start battery in an emergency .

Yes mate will be taking it outside. I do have a river boat already down there.

The boat is an old one but with a few new gadgets in it, it should be a good outside boat.

19ft Pride Gazelle 140hp Johnson. The motor is old but has good compression and starts easily and revs hard. Plenty of fishing room and the main reason I bought it.

Frank

[XD351]

Nice looking boat ! You can’t kill an old johno or evinrude . My mate had to replace the battery in his boat coz he left the sounder on and killed it , I told him to fit two batteries so one is dedicated to the motor , the other is for the electronics but he is too stingy and won’t listen to me so I won’t go out in his boat . I have been caught before by a weak battery that was drained down by the lights and wouldn’t crank the motor over - oddly enough it was his old man’s boat !

[frankS]

The boat is filthy at the moment as it's been sitting around for a while (I assume) .

After I give it a karcher and a bit of a tidy up I will post some proper photos of it.

But for now here is what the fishing room is.

It has those horrible back to back seats in it. But they are quite comfortable with storage under them so I will be leaving them in for the time being.

you can see it needs a good clean out.

Frank

[XD351]

Nothing a good scrub won’t fix! At least the seats are not ripped !

[fragmeister]

Hey Frank,

That interior looks like it will come up well after a clean.

On the battery question... :Lots of good info already provided, but I would add that :-

1) Cranking batteries are more likely to fail if you completely discharge them

2) Deep cycle batteries are most likely to fail when you draw heavy currents from them.

So biting the bullet and getting a cranking battery is a good move.

 

Cheers

 

Jim

 

 

[Rebel]

Great looking boat.

Can't beat the old models.

[frankS]

On 7/23/2023 at 11:42 AM, XD351 said:

Nothing a good scrub won’t fix! At least the seats are not ripped !

I will be removing the drivers Back to back seat out as it is awkward to stand up while driving and I prefer to be standing while driving the boat.

Will replace with this one standing on a pedastal.

Had it sitting in the shed for a while so might as well get some use out of it.

Frank

 

[antonywardle]

If weight is an issue, i see you can now get lithium cranking batteries again

It will cost you about the price of three cranking batteries. I've not yet bought one to see

how they perform.