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p6rob

Battery maintenance

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Sorry. It's a battery question.

Since moving on the boat about 6 years ago, I've had to replace the batteries every two years. Up until the last set, I always bought sealed maintenance free lead acid as I didn't think I'd be regimented enough to keep an eye on acid levels, two of the three batteries are difficult to peer into the filler holes.

Getting on for two years ago, I thought I might be better at maintenance, so bought 3X 110 batteries. Initially I was fairly good at checking the levels but as they never needed topping, that soon slipped to 3 or 4 months between checks. Yesterday I checked them for the first time in probably six months and they still don't need any water adding.

They have however lost a bit of power. This isn't a major issue as I don't really consume much, the lights are LED, I occasionally run a vacuum from the generator but the engine is usually running at the same time.

Whenever I've fitted new batteries the Smart Gauge tends to show 13.2 volts at rest and after about two years this drops to about 12.8v. What I've noticed is at night, when there's no solar the diesel heater won't start because of low voltage. When it's doing it's start up sequence the Smart Gauge shows volts are around 12.3v. The heater is not a marine one, so I understand why it won't run. When the batteries are tired if it's a bit nippy but not worth getting the stove going, I'll run the engine while the heater starts up to keep the volts high enough. Once the startup has completed, the engine gets turned off and the heater will run for several hours quite happily.

 

Getting to the point.

During winter I charge the batteries from the engine at about 1200rpm for an hour or two every few nights and about six hours at the weekend.

During the sunny season, the two solar panels do the charging through an outback mmpt controller.

Is there a setting I should change to make the charging more aggressive and if so, with proper maintenance, would that make the batteries last longer than two years?

 

I don't necessarily think replacing batteries every two years is bad but when I hear of people getting 5+ years, Having never had to top up these batteries makes me wonder what they do differently.

 

Cheers

 

Rob

 

 

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10 minutes ago, p6rob said:

Whenever I've fitted new batteries the Smart Gauge tends to show 13.2 volts at rest and after about two years this drops to about 12.8v.

A fully charged battery 'at rest' will show about 12.8 - 12.9 volts.

What you are measuring at 13.2 volts is the surface charge on the battery plates and is not the true battery voltage.

 

To measure correctly the battery charger must be turned of, solar panels covered or disconnected and the engine not run.

Use 'something' (headlight) for a few minutes to use up the surface charge, the switch off everything so there is no charge going in and nothing coming out.

 

After 2+ hours like this then you can test the battery voltage.

 

The thing to remember is that there are two characteristics of a battery :

Voltage

Capacity.

 

Capacity is measured in Ah (Amp hours) and you typical new battery is 110Ah.

Unless you recharge FULLY the battery it will start to sulphate and the capacity is reduced, you then fail to recharge it fully and it gets a bit more sulphate, you fail to recharge and ………….

As the battery gets more and more sulphate the battery loses its capacity so your battery will become capable of holding less and less Ah, it may for example drop :

 

95%

90%

85%

…..

…..

…….

…….

25%

 

A battery can be any 'size' and be 12v (12.8v) - a battery for a watch or a camera can be 12v but will have a low Ah capacity.

 

As you battery capacity drops, it struggles to provide enough power to start something with a heavy start up current, this then drags the voltage lower and lower as it tries to pull more current.

 

Basically it sounds like you are undercharging your batteries.

 

"an hour or two every few days" is not enough.

 

Do a proper electrical audit then you will know how much you use and how much you have to replace.

 

You can consider your batteries to be charged when the charging voltage is above 14.4 volts, AND, the current is 1% of the battery capacity (so for a 200Ah battery bank the charge current should be 2A). It needs to be at these figures, and not change, for 2 hours.

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3 hours ago, Alan de Enfield said:

 

Do a proper electrical audit then you will know how much you use and how much you have to replace.

 

And bear in mind a 90A alternator won't produce 90 amps for more than a few seconds.  It isn't long before the current will drop to about 30 amps even with a fairly well discharged battery. Most of the charging will be at less than 20 amps.

 

This is why a couple of hours every other day is not enough for most users, even with quite modest use.

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Thanks. I suspect I'll just keep replacing the batteries every couple of years until li-ion controllers become affordable but might take these ones into work and use their fancy charger to see if that perks them up a bit first.

 

The isn't much electrical stuff in use. If all the lights are on they draw under 3 amps and the lights might be on for six hours per day in winter, The water pumps run for about 15 minutes a day in total. Phone charges overnight but the internet dongle is always plugged in.

 On the rare occasions I use the TV, the engine tends to be running, same with vacuum.

Only really use the laptop on its battery. 

The diesel heater gets used about 30 times a year when the weather is chilly but not worth having the stove going.

Fridge and water heater are both gas.

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An equalisation charge at say 15 volts for a couple of hours may just increase the capacity a bit, allowing you to limp into the autumn. As said Lead batteries like to be fully charged every day, certainly every few days, that usually means charging for at least 5 hours every other day in winter. Because the batteries control the charge rate over 80% full and gradually accept less current, the last hour can start at 4 amps and finish at 2 to get to 100%.

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On 17/04/2020 at 10:14, p6rob said:

Sorry. It's a battery question.

 

Getting on for two years ago, I thought I might be better at maintenance, so bought 3X 110 batteries. Initially I was fairly good at checking the levels but as they never needed topping, that soon slipped to 3 or 4 months between checks. Yesterday I checked them for the first time in probably six months and they still don't need any water adding.

 

Whenever I've fitted new batteries the Smart Gauge tends to show 13.2 volts at rest and after about two years this drops to about 12.8v. What I've noticed is at night, when there's no solar the diesel heater won't start because of low voltage. When it's doing it's start up sequence the Smart Gauge shows volts are around 12.3v. The heater is not a marine one, so I understand why it won't run.

 

Cheers  Rob

 

 

Rob, thinking about the wires that run from the batteries to the swtich panel and on to the heater, what sort of length are they and are they heavy duty, eg, thick.  Had a similar problem with a portable fridge.  Replaced the thin wire with much thicker and boom fridge fired up and ran flat out promptly freezing me sandwiches.  Would be easy enough to check with some extra cable temporary rigged to see what happens next time the heater fails to start.

 

Or perhaps that's as good as it gets, but are you able to get those batteries back to 100% frequently? if not and living on board you may not be able to that could be all you can achieve.  But run a check on the wiring.  

 

12v Planet have a wire calculator half way down this page which may be helpful.

 

Pete

 

https://www.12voltplanet.co.uk/cable-sizing-selection.html

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