Battery Bank

[goboatingnow]

What the response was saying was nonsense was that solar chargers contribute to stray current corrosion. That fact is nonsense.

[cal40john]

Originally Posted by noelex 77

A small solar panel, say under 10w is fine connected to a large battery bank without a controler. This will replace the self discharge and keep the battery bank happy.
Stray current problems are much more common when AC battery chargers are used without an isolating transformer.

Originally Posted by Seahunter

Nonsense.

Originally Posted by Tristan

Noelex is right -it's not nonsense. The trickle charging current should be around C/300 (chemistry dep.) which in case of larger battery bank, let say 1000Ah would be ~3A and this is around 40W solar panel.
Stray current problems are AC related. You do not have common ground with the other boats in the DC circuit.
T.

Nolex actually said UNDER 10 W.

Tristan give C/300, which for a 10 W panel (at .76 amps) works for a not less than a 230 amp-hr bank. Nolex said less than 10 W for most banks, 230 amp-hr is not an unreasonable size for a house bank.

From: Charge Controllers for Solar Electric Systems

Do I always need a charge controller?

Not always, but usually. Generally, there is no need for a charge controller with the small maintenance, or trickle charge panels, such as the 1 to 5 watt panels. A rough rule is that if the panel puts out about 2 watts or less for each 50 battery amp-hours, then you don't need one.

This source indicates that a 10 watt panel would work without a charge controller on a 250 amp-hr bank.

John

[noelex 77]

Originally Posted by Seahunter

Even at 10 watts output without a controller a solar panel nearly .75 amp per hour (over 18 Ahrs per day) will be produced. This is enough to boil a wet cell away in a matter of days. As well a calculation based on 13.2 VDC (closer to a real voltage) and 10W produces nearly .76 Amp not .6 Amp.

Seahunter I do not want to get involved in any of the long winded negative threads that can sometimes occur in this type of forum, but to help everyone’s understanding have a look at your battery monitor when your solar controller has fully charged the batteries and is in float mode. (or measure the battery input with a multimeter)


What is the reading?


Unless your battery bank is small I guarantee it will be over the 0.76A you are concerned about.


( Incidentally a 10w solar panel will not produce 0.76A without a MPPT controller Solar panel output is rated at Vpm or voltage at load. This is typically about 17-18v. Unfortunately solar panels will not produce much more current at the more typical battery voltages. This is a characteristic of all solar panels and is the principal that MPPT extract slightly more current from solar panels

If we take the common Kyocera 10w panel it will produce under ideal conditions 10w at 17.9V or 0.56A . Unfortunately at the 13.2 V you quoted it will still produce the almost the same current.

Without a controller (so no MPPT effect) 0.6A from a 10w panel would be an very good result. In practice only seen, briefly, when the sun was very strong, in cold conditions, when the panel was angled perfectly, and sun emerged behind a cloud. The combination of direct sunlight as well as light diffused from the nearby clouds can raise the irradiance above the rated 1000w/square meter.
Without a MPPT controller the 0.76 A you expect from Ohms law will never be seen, even briefly under the best conditions.

The 0.6A I used for a 10w panel, directly connected to the battery, is accurate, or optimistic )




!8Ahrs from a 10w panel is also much too high. I am crusing in Greece at the moment, with a very high insolation value in summer. My 330w panels would produce 33X18 = 594 AHrs based on your calculations.

I wish this was the case, but 150-175 Ahrs is a good result on a summers day.

[Jacana]

Thanks for the info. so far.
My new battery bank- 4 Power Sonic 6V 213AGM's.Link 2000 system.
I use my boat daily so get regular re-charge via motors and trickle charge via solar.After installing I fully charged the battery bank and before I start the motors have noted the voltaged down,the only item that uses battery power overnight is the onboard freezer.Volts noted before morning start-1/10/2011-12.95 3/10-13.25 5/10-13.6 7/10-12.95 11/10-13.3 17/10-13.00 19/10-13.1.
As per my original question should I hook up to shore power nightly and keep fully charged or is it better for the battery bank to just fully re-charge when voltage is low and if so at what point do I fully re-charge.
Cheers
Geoff.

[Teeto]

If you have a smart charger you can plug into mains each night and it will charge the batteries as needed. It will even choose which batteries need more charging. It will also control solar input during the day to prevent overcharging.
The smart charger (xantrex and TBS are two types) takes all the worry out if it. Otherwise you can cook them in a very short time.

[noelex 77]

Originally Posted by Jacana

Thanks for the info. so far.
My new battery bank- 4 Power Sonic 6V 213AGM's.Link 2000 system.
I use my boat daily so get regular re-charge via motors and trickle charge via solar.After installing I fully charged the battery bank and before I start the motors have noted the voltaged down,the only item that uses battery power overnight is the onboard freezer.Volts noted before morning start-1/10/2011-12.95 3/10-13.25 5/10-13.6 7/10-12.95 11/10-13.3 17/10-13.00 19/10-13.1.
As per my original question should I hook up to shore power nightly and keep fully charged or is it better for the battery bank to just fully re-charge when voltage is low and if so at what point do I fully re-charge.
Cheers
Geoff.

Yes hook up shore power every day and leave it connected, providing you have a good quality multi stage charger. Fully recharge as often as possible.
Other battery chemistries like NiCad batteries want to be discharged periodically , but not lead acid they have the longest life when they are fully charged and discharged as little as possible. (occasionally stirring up the electrolyte with a shallow discharge and slight overcharge and equalization is helpful for some lead acid batteries chemistries, but not all.)

BTW those battery voltages are too high to be correct if you have a load (the freezer) and no charging before measuring the voltage. If the batteries were charging via shore power or solar when you took the readings, which I suspect is the case, the voltage does not directly reflect the battery state of charge. The battery voltage needs to compensated for the charge (or discharge) current (and temperature)+ history, to determine the batteries true state of charge.
In practice this means that the voltages measured are a very poor and inaccurate way of determination of the all important battery state of charge.
A battery monitor counting the AHrs in and out is better.

[Jacana]

Freezer is only thing left on during the night.When i do battery check in morning the freezer is not running,generally after I fill up with the days drinks etc the motor will come on so no load on battery bank.
When you say reading too high,how high should they go.
Cheers
Geoff.

[mikefossl]

Originally Posted by Seahunter

Even at 10 watts output without a controller a solar panel nearly .75 amp per hour (over 18 Ahrs per day) will be produced. This is enough to boil a wet cell away in a matter of days. As well a calculation based on 13.2 VDC (closer to a real voltage) and 10W produces nearly .76 Amp not .6 Amp.

I'm not sure I understand how .75 amps per hour will "boil a wet cell away in a matter of days". Regardless of that a 10 watt panel will never make full power and certainly not at night which your calculation suggests.

[noelex 77]

Originally Posted by Jacana

.
When you say reading too high,how high should they go.
.

Its very difficult to deduce much about the state of charge of a battery from voltage alone, but a fully charged battery if rested (no input or output for 24 hours, or longer with some batteries) will read about 12.6-12.7 V depending on temperature and battery chemistry.
The voltage of a fully charged battery will read much higher if it is being charged, or has been charged recently. Or lower if there is a load, or has been recently

The voltages you quote between 12.95 and 13.6 indicate the battery was charging when you made the measurement. (or the meter is defective).
This voltage will be strongly influenced by the charging current and does not tell you much about the battery

[mitiempo]

Here's Trojan's chart for battery state of charge of a rested battery.

[Jacana]

Thanks for the chart.
So at what level of voltage should I hook into shore power to recharge the battery bank?
Cheers
Geoff.

[noelex 77]

12.6+ V.

[mitiempo]

50% state of charge or 12.06 volts resting. Ideally you should have a good battery monitor as a voltmeter does not tell you much if the batteries are in use.

[noelex 77]

Originally Posted by mitiempo

50% state of charge or 12.06 volts resting. Ideally you should have a good battery monitor as a voltmeter does not tell you much if the batteries are in use.

There is a risk of confusing people here.
For reasonable battery life a good rule of thumb is the batteries should not be discharged below 50%, other than occasionally.
Battery life will be longer, however, if you recharge sooner and discharge the batteries less. If we keep the discharge to only 15-20% most batteries will last close to 50% longer.
If you have shore power and a good battery charger, put them on charge ASAP. Do not wait until they are at 50%. The charger will keep the batteries at 100% and this gives the longest life for lead acid batteries.
Other battery chemistries like NiCad and Lithium batteries have different requirements.

[Jacana]

Your right about that,I am confused.
My batts. are AGM just wondered if anyone knew the correct way to look after same for long life.Seems like advice is going in circles.
Bottom line do I hook up to shore power each night or is it best to run batteries down a bit before re-charge.
Cheers
Geoff