Battery drainage, urgent problem

[Chris_Robb]

I only wish the message would get through! We can only keep hammering away promoting correct battery management.
Sadly, as demonstrated by posts on a nearby thread, a head in the sand attitude seems to prevail - ie if I don't have battery problems (for now) my charging regime must be fine.

The Golden rules:
Avoid discharging below 40% for maximum battery life (about 11.95v no load on a rested battery)
Never leave a battery partially discharged
Keep a check on the electrolyte level of non sealed batteries, especially if rapid charging is practiced.
Use multi stage charging for ALL charging
Remember that without a multi stage regulator, the battery is unlikely to get above 85% charge, so the useable capacity is 85 - 40 = 45% of the rated AH capacity. In other words, if you use 50AH between recharges, you need to fit a 100ah battery and the charger needs to be able to put about 60AH back in the available charging time.
Fit a digital battery monitor such as the Nasa BM1 - if you never see over 14v even with the load removed, then you are undercharging.

Yes, people and engineers seem utterly ignorant of the obvious! I down graded my charging regime on the sterling from 14.8 to 14.4V. The difference in rate of charge was significant. With well discharged batteries at 14.8v, I would see an initial charge of nearly 100amps. WIth 14.4v I get only 70amps. It very significant.

A simple rule might be: Charging voltage 14.8v less standing voltage 12.8v = 2 volts difference.

If you charge at a lower voltage - lets say 14v, then 14-12.8 = 1.2v diff. A difference of nearly 40% reduction in charge rate.

I know its not actually linear but the principle works, I think.

One question I would like answered:
In modern automotive alternators they are internally regulated at 14.4 volts. there appears to be no float voltage say after 6 hours of motoring. It appears that it does not impact on battery life of a car, The perceived wisdom is once the battery is full the alternator should go to flat charge - say 13.8V. So even if you have a special regulator, it cannot override the alternator if charging at a higher voltage.
Some people say that if they have one of these modern alternators, why do they need a Sterling unit (or similar)?

 

[GHA]

Remember that without a multi stage regulator, the battery is unlikely to get above 85% charge,

That's a bit confusing, how so?
If you have a PWM solar regulator set to , say, 14.8v (as my marlec is), how can that never get past 85% ? It seems to do OK if there's enough sun.

 

[halcyon]

That's a bit confusing, how so?
If you have a PWM solar regulator set to , say, 14.8v (as my marlec is), how can that never get past 85% ? It seems to do OK if there's enough sun.

Depends on the actual voltage plot, you need a scope to check, but to fully charge a flooded lead acid you are looking at 15.6 volt. Your solar cell will produce a flat 14.8 voltage, but if for example you had a simple transformer rectifier charger with a simple controller, you can see 15.6 volt at the top of the pulses, thus full charge without a complex multi stage charger.

Brian

 

[ianj99]

That's a bit confusing, how so?
If you have a PWM solar regulator set to , say, 14.8v (as my marlec is), how can that never get past 85% ? It seems to do OK if there's enough sun.

If it has no multi stage ability, then I would guess the current at 14.8v is small enough not to cause a problem. Equalisation takes many hours at a small current - Victron quote 8% before dropping down to the float voltage.
Do you know what the current is flowing into the battery at 14.8v? (have you checked this is the voltage on the battery terminals?)

 

[ianj99]

Yes, people and engineers seem utterly ignorant of the obvious! I down graded my charging regime on the sterling from 14.8 to 14.4V. The difference in rate of charge was significant. With well discharged batteries at 14.8v, I would see an initial charge of nearly 100amps. WIth 14.4v I get only 70amps. It very significant.

A simple rule might be: Charging voltage 14.8v less standing voltage 12.8v = 2 volts difference.

If you charge at a lower voltage - lets say 14v, then 14-12.8 = 1.2v diff. A difference of nearly 40% reduction in charge rate.

I know its not actually linear but the principle works, I think.

One question I would like answered:
In modern automotive alternators they are internally regulated at 14.4 volts. there appears to be no float voltage say after 6 hours of motoring. It appears that it does not impact on battery life of a car, The perceived wisdom is once the battery is full the alternator should go to flat charge - say 13.8V. So even if you have a special regulator, it cannot override the alternator if charging at a higher voltage.
Some people say that if they have one of these modern alternators, why do they need a Sterling unit (or similar)?

Also don't forget the voltages are temperature sensitive closer to 15v is needed in very cold weather, and closer to 14v in hot weather, or if the batteries have heated up due to high charging currents.
Most batteries have a manufacturers recommended max charging current - 10-13% of C20 (AH capacity at 20hr rate) (Optima batteries have no limit) so this is yet another factor.

Re automotive alternators - the engine ecu can control the alternator, though I think this is to switch it off in the event of overvoltage to protect the electronics but maybe they can switch it to float volts as well?

 

[GHA]

If it has no multi stage ability, then I would guess the current at 14.8v is small enough not to cause a problem. Equalisation takes many hours at a small current - Victron quote 8% before dropping down to the float voltage.
Do you know what the current is flowing into the battery at 14.8v? (have you checked this is the voltage on the battery terminals?)

Were we talking about equalization?

And as batteries are a chemical process isn't the whole concept of the "full bucket" a little bit flawed.

Ignoring temp, I usually go that if the voltage is in the high fourteens and the battery is accepting less than 1% C then there's not much to worry about.

A very useful bit of kit is an accurate voltmeter wired directly to the batt terminals and visible from your favorite seat .

A few quid off ebay.

 

[ianj99]

Ignoring temp, I usually go that if the voltage is in the high fourteens and the battery is accepting less than 1% C then there's not much to worry about.
A very useful bit of kit is an accurate voltmeter wired directly to the batt terminals and visible from your favorite seat .
A few quid off ebay.

I don't disagree, but the point is that the OP was not seeing more than 13.5, implying the batteries were not being charged adequately either due to insufficient charging current or a poor regulator so he should have been worried....

A digital voltmeter off ebay is useful, but you still need to rest the battery to get an accurate reading of its state of charge. Ie a reading of 12v on load tells you little about the state of charge.

 

[BabaYaga]

Yes, people and engineers seem utterly ignorant of the obvious! I down graded my charging regime on the sterling from 14.8 to 14.4V. The difference in rate of charge was significant. With well discharged batteries at 14.8v, I would see an initial charge of nearly 100amps. WIth 14.4v I get only 70amps. It very significant.

Are you saying that you see 14.8 volts and nearly 100 amps going in AT THE SAME TIME?
I find those numbers quite impressive. Would be interesting to know the alternator capacity and size of bank.

 

[[70521]]

Why is it so hard for this simple concept to be grasped?

Because there is no definitive text on batteries, the advice given is confusing and often contradicts what people have been told/taught/read/dreamt or studied.

If you have a definitive text, I'd be more than happy to read it, just in case I do win the lottery and can do that single handed non-stop circumnavigation.

 

[halb]

I have 4 batteries aboard, 2 Trojan 105's, 1 starter and 1 for the bow thruster/windlass aboard Demoiselle, she is kept on a swinging mooring therefore no shore power. To keep everything topped up there is a Rutland 913 and 2x80 amp solar panels all controlled by a Marlec HRDi regulator, this unit does work very well, keeping the batteries at 14.4. The Marlec is very easy to install, even for an electrical numpty like me! When I've had any queries the Marlec/Rutland tech department are very helpful and give advice in an easy to understand way.
Jon
(No connection with Marlec/Rutland just a very happy customer )

 

[sailinglegend420]

.......One question I would like answered:
In modern automotive alternators they are internally regulated at 14.4 volts. there appears to be no float voltage say after 6 hours of motoring. It appears that it does not impact on battery life of a car....

This is because these modern regulators are temperature compensated to protect the battery, so when the engine compartment heats up the regulator assumes the battery is in the engine compartment and reduces the charging voltage. So after a while the actual charge voltage will fall to maybe 14v, well below the gassing voltage of 14.4v which is why car batteries don't get overcharged.