my boat battery

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    Posted: 02 Oct 2021 at 11:05am
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THis is old hat thats no doubt been discussed before.

My boat battery failed after 2 and a half years. Thats pretty short time.Ive bought a new one, ok.  

Im not very knowledgable re batteries. Im thinking that, the battery doesnt like dropping to low charge. Ive got a anchor winch. It drains heaps of charge out of the battery. Then I run, mostly very short trips, to other places and back home. Possibly not enough to fully charge the battery. So, is it likely, the battery has dropped (and stayed) too low, and thats caused it to fail. 

With the new battery, when I raised the anchor, I saw (on my sonar voltage readout), the voltage dropped from about 12v to 10.7v; that seems pretty low?
Its a 1000w anchor winch, thats a high drain on the battery.

I will fully charge the battery (with a charger), and the see how much the voltage drops on anchor raising.

I would appreciate any words of wisdom on this.
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 11:34am
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Maybe a bigger battery if it will fit..
If you always do, what you've always done. You will always get, what you have always got
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Rex ... I have been there but now have the comfort of knowing
am not likely to get caught out whilst out on the water since having a couple of backup features installed ... you are welcome to check them out once L2 is announced & restrictions are lowered.Text Colour

Until it happens to us we seldom think about how vulnerable we are to battery failure particularly as modern day batteries seem to be much more prone to dying with little or no warning compared to their predecessors.

Of course firstly motor should be running before & during the winch being implemented as it is the major draw on any battery power, not that it will totally compensate but at least if motor is kept running you should be assured of being able to return to launching/retrieving place ... however am certain with your wealth  of experience you will be well aware of all that so will move on to other pitfalls that can be encountered due to a flat battery.

AlanL is the only person I know that has been able to rope start my 90hp Merc & that was when still on the trailer ... I certainly cannot manage to do so.

Next GPS/chart plotter possibly dead along with installed VHF, bilge pump & motor tilt ... mob ph could also be out of cover.

A small portable jump start may manage to start motor but have to take care cable clamps don't short out on anything particularly on ali hulls but seem to recall your new boat is FGlass.

On two occasions my main emergency backup system has come to the rescue ... would not be without it. 
Scored a much needed hair cut this morning so now on the way to Mitre 10 to take back the hedge trimmer !!
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Put any significant load on a battery and the terminal voltage will drop. 100 is quite small for an anchor winch, I'd expect it to be drawing more than 10 amps.

Think in amp hours. If it takes 2 minutes to pull an anchor up using 480 w winch. Assume it is drawing that. P=vxa, 480 divided by 12 volts is 40 amps.

You used that current for 2 minutes.
If your motor can charge at 5 amps, that is one eighth of what you were drawing, so you need to charge for 8 times the time...16 minutes to replace that charge.

So, if you up pick and move lots, short distances, you might be slowly draining your battery. If this is only day trips, then a good charge overnight when you get home, will top the battery up. No real harm done.
You then need to use a maintenance charger if you don't use the boat at least every month..

No battery likes to sit even in a partially discharged state for long. It will die.
Anything over 50% discharge at any time will cause damage.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Originally posted by letsgetem letsgetem wrote:

THis is old hat thats no doubt been discussed before.

My boat battery failed after 2 and a half years. Thats pretty short time.Ive bought a new one, ok.  

Im not very knowledgable re batteries. Im thinking that, the battery doesnt like dropping to low charge. Ive got a anchor winch. It drains heaps of charge out of the battery. Then I run, mostly very short trips, to other places and back home. Possibly not enough to fully charge the battery. So, is it likely, the battery has dropped (and stayed) too low, and thats caused it to fail. 

With the new battery, when I raised the anchor, I saw (on my sonar voltage readout), the voltage dropped from about 12v to 10.7v; that seems pretty low?
Its a 100w anchor winch, thats a high drain on the battery.

I will fully charge the battery (with a charger), and the see how much the voltage drops on anchor raising.

I would appreciate any words of wisdom on this.
Gidday can you tell us what motor and battery size you have.
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Post Options Post Options   Likes (0) Likes(0)   Quote letsgetem Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 2:07pm
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Its a 90hp Mercury 4 stroke. The battery is 530cca 52AH.
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Originally posted by letsgetem letsgetem wrote:

THis is old hat thats no doubt been discussed before.

My boat battery failed after 2 and a half years. Thats pretty short time.Ive bought a new one, ok.  

Im not very knowledgable re batteries. Im thinking that, the battery doesnt like dropping to low charge. Ive got a anchor winch. It drains heaps of charge out of the battery. Then I run, mostly very short trips, to other places and back home. Possibly not enough to fully charge the battery. So, is it likely, the battery has dropped (and stayed) too low, and thats caused it to fail. 

With the new battery, when I raised the anchor, I saw (on my sonar voltage readout), the voltage dropped from about 12v to 10.7v; that seems pretty low?
Its a 100w anchor winch, thats a high drain on the battery.

I will fully charge the battery (with a charger), and the see how much the voltage drops on anchor raising.

I would appreciate any words of wisdom on this.

A friend of mine has had the same/similar problems.
Seemed to have solved it with a permanent trickle charger when not using the boat.
Batteries lasting ages now.
Also as Bazza says, always advisable to have the motor running when raising the anchor. 
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Maybe check the output from engine charging system?
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Originally posted by letsgetem letsgetem wrote:

Its a 90hp Mercury 4 stroke. The battery is 530cca 52AH.
90 4s has a good output alternator 35amp and the battery size looks to be ok. As Bazza says you should always start your engine first before using the winch. I like the new smart chargers I’ve got a 8 cycle charger and just leave it connected all the time. I would suggest checking all your electric connections to make sure there’s voltage drop because seeing your fish finder drops down to 10.7v seems really low lucky it even starts at that. So it makes me think you might have a bad connection somewhere between the battery and the fish finder. Perhaps put a voltmeter across the battery terminals and see what the voltage drops to there when you run the winch. The engine and the winch would run off a different battery feed so maybe that’s why your only seeing the low voltage reading at you finder.

How did you know your last battery was stuffed, did you take it in and get it load tested.
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Post Options Post Options   Likes (0) Likes(0)   Quote letsgetem Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 3:41pm
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Three points -

Oh my mistake - its 1000w anchor winch (not 100).

The battery voltage drops from 12v to 10.7v when the anchor winch is pulling up - not when starting the motor.

The previous battery, wouldnt start the motor - not a peep out of it. I took it to a garage and they load tested and said its stuffed.
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 4:20pm
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Ok that makes more sense, what does the voltage return to. The winch should have a working load about 80 amps. Which shouldn’t take to much out of your battery if it’s fully charged. As above maybe look at a small ctek smart charger or something similar.
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The concept of starting the outboard and having running while using a winch/ capstain, is not about charging.
 Alternators have next to no charge till hit around 1200 to 1800 rpms.
 The reason is that if you have a dud battery, and/ or charging circuit , at least the engine is fired up to get home.

As per others above.. batteries , any type dont like being discharged and stored partly charged, espec modern batteries... In saying that I maintained they actually have a far longer life.

About a 530 cca is ok for just your engine spec, and gps, sounder few other low current items... A larger battery with greater storage would certainly help longevity using high current winches. Something the battery ppl should advise on.

Even so getting home and throw on a smart charge (ctek) 8 stage charger...an maintain that charge between trips.

 This is all assuming that your battery connections, isolating switch connections etc, the battery top is kept clean and that the charging system is actually working.
These will not only cause extra current draw to items but also effect the rate the alternator re charges.

In general a fully charged battery will give you 1 1/2 good days trips out fishing before you notice that when you trim the engine it sounds different and weak.

Check  and clean, re grease connections, then check its charging...
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Post Options Post Options   Likes (0) Likes(0)   Quote letsgetem Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 5:57pm
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According to the manual (for the Mercury 90hp), the alternator charges at 50amps.

When its charging, the voltage rises from 12v to 14v. 

And I can confirm the motor alternator does not charge until over 1000rpm, ie not at idle. 
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Originally posted by letsgetem letsgetem wrote:

According to the manual (for the Mercury 90hp), the alternator charges at 50amps.

When its charging, the voltage rises from 12v to 14v. 

And I can confirm the motor alternator does not charge until over 1000rpm, ie not at idle. 
Mate the reason for starting the motor first is if the battery get to flat to start the engine while your running the winch.
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 7:46pm
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You should be charging at 1000 rpm. My Merc 2S has about 10A at 1000 rpm or there-abouts - and the manual specs say so too. You will have pretty much the same charging system. If the motor is turning, it is charging. Just at the low end of output.
But as Steps said, and you have deduced. The battery does not like being left half charged.
If you are only short running and potentially short charging , a trickle chargewhile the boat is stored is the answer. I leave all my boat and car batteries on trickle - for up to 6 mths. In the boat I am using right now a $100 battery (not even Marine) ), 3 yrs old - and still holding 12.8 V. It had been on trickle for 6 mths and had 12.8V after standing for a day or two. And still does. And cranks the engine no problem.
Also most batteries don't like rapid deep drain - but you can't avoid that with a winch. Is it Deep Cycle? Should be - for that job.
Alan

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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2021 at 8:03pm
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approximate
amperes:
RPM AMPERES (9A charger)
Idle 4.0
1000 8.0
(14 Ampere Stator) 2000 11.0
3000 13.0
4000 14.0
5000 14.0
RPM AMPERES
Idle 5.0
1000 10.0
16 Ampere Stator 2000 16.0
3000 17.0
4000 18.0
5000 18.0

The copy /paste got messed up. This is early Merc 2S around 90HP. Somewhere I have more recent specs but can't find right now. There are usually 3 charge options - small/med/large. But at 1000 rpm you should be charging around 10A. If not - you have a problem.
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assume you have the now standard AGm chemistry battery - you, like many people are finding they dont seem to last as long as the old FLA batteries.

there are two issues you need to be aware of that are hurting your battery;

the anchor winch is drawing at least 80amps - possibly more if your wiring or terminals arent ideal - and whilst as mentioned above, the total A/hrs removed from the battery arent that many because of the short winching duration - the RATE of current is getting quite high - 80+ AMps is approaching double thew capacity of your batt and many manufacturers recommend against very high charge/discharge rates - often only 100% of capacity. this is where lithium is a big improvement - 500+% charge/discharge rates are no issue

secondly - AGM do not like being left at anything less than 'full voltage' for very long - best practice is to bring them up to full once a week. even with everything disconnected, they will often have a self discharge rate of 1 - 3% per month -  so they need regular attention.

basically you should consider getting a larger battery next time so your winch isnt asking too much from it in terms of 'rate of current draw' and get a decent multi-stage smart charger that can be left plugged in permanently when the boat is stored on the trailer between outings
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Post Options Post Options   Likes (0) Likes(0)   Quote letsgetem Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2021 at 9:21am
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Good stuff, thanks.

According to the motor specs (2018 90hp 4 stroke) - the alternator output is 50amps. THat appears a lot higher than the 2 stroke amps mentioned. 

One thing Im bothered by. THere doesnt appear to be a way of measuring the % charged of the battery. If there was, I would know whether the battery needs charging - and put the charger on it. Has anyone figured a way of measuring this? 
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Originally posted by letsgetem letsgetem wrote:

Good stuff, thanks.

According to the motor specs (2018 90hp 4 stroke) - the alternator output is 50amps. THat appears a lot higher than the 2 stroke amps mentioned. 

One thing Im bothered by. THere doesnt appear to be a way of measuring the % charged of the battery. If there was, I would know whether the battery needs charging - and put the charger on it. Has anyone figured a way of measuring this? 
I use one of these, simple easy to install and read, I just hang mine of the side of the battery box where I can see it any time and my ctek smart charger plugs straight into it.

https://www.marine-deals.co.nz/smart-battery-chargers/ctek-comfort-indicator-eyelet-m8-8-4mm?gclid=EAIaIQobChMIpNvcrces8wIVgiQrCh2RBQDFEAQYASABEgJXePD_BwE
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2021 at 9:45am
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BH covers that above...
just put it on a maintenance charger once a week or simply leave on the smart charger.
 And make sure your chargers are the correct charger for the type of the battery, otherwise you will over charging a little or undercharging and either of these also drops the battery life dramatically.

 Also that 50 amp rating is not 50 amp at 1000 rpms. The 1000 rpms is where it starts to charge.
 
There is also another long term issue with a battery too small for the engine , and or too small for the engine and other large loads at the same time... If your voltage drops too low, you CDI / ignitions sealed regulators  have to draw more current to maintain their required power draw.
 More current means they then heat up, and they do not like running too warm or hot.
 And they are expensive to replace...

Never run the engine disconnected from the battery either.. that kills the sealed regulator/ tach unit, and they are not cheap either.

From memory my manual says run a min 630cca battery
I have a 760 or 780..because running high pressure wash down pump or the capstan from 50/ 60m.
 The Local auto electrician only has 2 rather 'oversized ' marine batteries in stock. Reason being he doesnt get ppl coming back because of early battery failure.
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