The never-ending saga of battery charging.

[[3889]]

Yet another battery question, I'm afraid.
When I charge off the mains I tend to be hooked up for 18 hours. My charger gives 25A and has a user-controlled boost setting which charges at 14.2V for the first 4 hours then drops to 13.7V. Often the charging is interrupted (timed hook up) and the boost period restarts.
My questions are: will the batts, 240 Ah, charge fully without the boost enabled? Will restarting the boost charge regularly after disconnection damage the batteries?

Edit. Standard lead acid

 

[dom]

I'm wondering if your batts are sealed or open - if open don't worry as you can just top up with water.

if sealed, are you sure your charging system has only two phases: 14.2 and 13.7V? I ask because many of the newer 3-stage chargers have a higher phase of around 14.8V, which is incidentally all you'd have to worry about here. A highest phase of 14.2V won't do any serious/noticeable damage to your batts; indeed standard machine sensed alternators are normally set to 14.2/3V, sometimes even 14.4V. Restarting your charging system is therefore no worse than going for a spin!

 

[VicS]

Yet another battery question, I'm afraid.
When I charge off the mains I tend to be hooked up for 18 hours. My charger gives 25A and has a user-controlled boost setting which charges at 14.2V for the first 4 hours then drops to 13.7V. Often the charging is interrupted (timed hook up) and the boost period restarts.
My questions are: will the batts, 240 Ah, charge fully without the boost enabled? Will restarting the boost charge regularly after disconnection damage the batteries?

Edit. Standard lead acid

If your charger delivers no more than 14.2 volts then you have no worries about over-charging.

I assume that 25 amps is the maximum output from the charger but do you know what the charging current at any point actually is? Unless it is a constant current charger the actual current may be somewhat less than 25 amps and in the 4 hour boost period may not fully recharge the batteries if they are significantly discharged.

13.7 volts is only going to deliver a float or maintenance charge perhaps ( guessing) only around 3 amps into a 240Ah battery.

I think, therefore, that with the charging regime you describe under charging is the most likely problem unless the " boost" stage is restarted at least once.

My own "smart charger" charges at a constant, user selected, current until the battery terminal voltage reaches 14.4 volts . Then it switches to a complex float/ maintenance mode

 

[BabaYaga]

My questions are: will the batts, 240 Ah, charge fully without the boost enabled? Will restarting the boost charge regularly after disconnection damage the batteries?

1. No, and as already mentioned you run the risk of undercharging your batteries even with the 'boost setting', because the batteries will not get a full absorption charge.
2. No, it will help them.

 

[pvb]

My charger gives 25A and has a user-controlled boost setting which charges at 14.2V for the first 4 hours then drops to 13.7V.

The boost voltage sounds very low. What charger is it? Can it be set to give different voltages?

 

[PaulRainbow]

Yet another battery question, I'm afraid.
When I charge off the mains I tend to be hooked up for 18 hours. My charger gives 25A and has a user-controlled boost setting which charges at 14.2V

Edit. Standard lead acid

14.2v is usual for gel/agm, for open cell (not sealed) it should be about 14.8v. You say 2user controlled", so change it.

 

[dom]

14.2v is usual for gel/agm, for open cell (not sealed) it should be about 14.8v. You say 2user controlled", so change it.

??

Quiddle is concerned about the repeated initiation of his 14.2V boost cycle given the nature of his power connection. The gassing voltage at 20C for a std flooded lead batt is typically around 14.45-14.5V. He therefore has little to worry about, except perhaps a slight undercharging issue over time.

If he resets his boost phase to 14.8V he will quickly ruin his batteries if they are sealed!

 

[pvb]

The 14.2v/13.7v settings which the OP quoted are typical of chargers designed to maintain back-up power supplies. It may be that he's using a charger which isn't designed for boat use.

 

[PaulRainbow]

??

Quiddle is concerned about the repeated initiation of his 14.2V boost cycle given the nature of his power connection. The gassing voltage at 20C for a std flooded lead batt is typically around 14.45-14.5V. He therefore has little to worry about, except perhaps a slight undercharging issue over time.

If he resets his boost phase to 14.8V he will quickly ruin his batteries if they are sealed!

He said in post one "Standard lead acid". He also said the settings are "user-controlled".

His current setup is unlikely to fully charge his batteries, he needs to change something.

 

[dom]

He said in post one "Standard lead acid". He also said the settings are "user-controlled".

His current setup is unlikely to fully charge his batteries, he needs to change something.

I think for most people a "standard lead acid" battery implies a normal light duty lead/calcium leisure battery, either sealed or open.

Follow your advice on a sealed one and the OP would risk ruining it in light of his intermittent power connection. I thought that was worth pointing out and still do.

 

[PaulRainbow]

I think for most people a "standard lead acid" battery implies a normal light duty lead/calcium leisure battery, either sealed or open.

Follow your advice on a sealed one and the OP would risk ruining it in light of his intermittent power connection. I thought that was worth pointing out and still do.

No harm in mentioning it, but my interpretation of "standard" means open wet cell.

 

[[3889]]

Thanks for all replies. Batteries are sealed so can't be topped up. Charger is a Cristec, supplied with boat, and can be set to 14.8v boost. However, resting voltage after charging is 12.8V which I take to mean fully charged? I have no means of measuring current at the moment. So, as long as prolonged 14.2V isn't harmful I'll leave things as they are. Cheers.

 

[Plevier]

Thanks for all replies. Batteries are sealed so can't be topped up. Charger is a Cristec, supplied with boat, and can be set to 14.8v boost. However, resting voltage after charging is 12.8V which I take to mean fully charged? I have no means of measuring current at the moment. So, as long as prolonged 14.2V isn't harmful I'll leave things as they are. Cheers.

I had the same charger on a Jeanneau. Not impressed with it, very noisy electrically and these badly chosen voltages with a timed only boost that restarts after a momentary mains drop out.
It's a difficult choice which setting to use. It rather depends on how heavily you use the batteries, how often the mains drops out restarting the boost, how long the boat is left with the charger on and whether you can find a way of topping up the batteries. I'm assuming you mean MF (sealed maintenance free) with liquid electrolyte, not AGM? If MF there is often a lid you can prise out, maybe under a stick on label, but some are permanently sealed. Don't try it with AGM!
As my case was usually light weekend use, with occasional mains outages, I stuck with the lower voltage as you have and it worked OK. 14.2V won't recharge enough in 4 hours after a significant discharge but repeated say 3 times it will without significant water loss. The bigger worry is the too low float voltage that will never make up for the low boost. In fact 14.2 isn't a boost, it's just a slightly high float:charge voltage that could be used for quite long periods without a problem. 14.2 is a not uncommon car alternator voltage now.
If the batteries are used more heavily or frequently and if there is a way of topping up, I would use the higher setting. If there is no load left on, you could use a simple plug in timer to switch the charger off after say 48 hours if mains dropouts are really frequent.

 

[[3889]]

Thanks, they are MF batts. I'll poke around under the labels but I rarely discharge below 12.4V resting so I don't think undercharging is a a big issue.
And yes, electrical noise is a MAJOR problem: no radio 4 LW on hook up

 

[pvb]

Thanks, they are MF batts. I'll poke around under the labels but I rarely discharge below 12.4V resting so I don't think undercharging is a a big issue.

Undercharging means that you don't ever fully charge the batteries, not to be confused with the depth of discharge.

 

[[3889]]

Is it too simplistic then to believe that a charge voltage of ,say 13.4V will, eventualy, fully charge a battery? The reason I ask is that on a previous boat I accidentally discharged the battery to the extent that the LEDs on the switch panel would not illuminate. After 2 weeks of charge from a 10W solar panel the battery was back to normal.
I'd assumed the simple hydrology analogue applied: if charging voltage is greater than resting voltage the battery will eventually become fully charged.

 

[crisjones]

The charger you have will probably get the batteries fully charged at 13.7V but it will take a long time. If the battery is only 25 or 30% discharged your 18hr plug in time will probably be enough, if 50% discharged it probably wont.
Charging voltages are a compromise between speed of charging and risk of overcharging / overheating, the voltages mentioned above have been decided upon by the battery manufacturers as being the most suitable for their batteries. A higher charging voltage will charge the battery quicker but may cause excessive gassing as full charge is approached - not desirable in sealed batteries!! A lower voltage will charge the battery but will take longer.
The solar panel you mention was probably unregulated and would be capable of producing 16 or 17V on open circuit so it would be perfectly capable of charging a normal battery over a long period of time. The battery itself would act as a regulator and would not overcharge with only a 10W panel.
The reason for charge voltages being higher than normal battery rest voltage is mainly to do with the internal resistance of the battery - you need to overcome this resistance to actually "force" current into the battery, hence the normal 14.2V for sealed batteries.
You also have the problem of what may be called "diminishing returns" as the battery approaches fully charged - near full charge the battery will accept less and less charging current so the last 10% of charging can take as long as the previous 30%. In this last 10% phase the 13.7V level will put charge into the battery and will eventually get to full charge, the 14.2V level will put a bit more charge in a bit more quickly but not vastly more.
In summary if you can manage to get 1 or 2 hrs of your charging done at 14.2V, particularly at the beginning then the overnight 13.7V should get the battery fully charged or very close.