Trickle Charge with Solar Panels

[nigel1]

Solar panels finally installed, 2 x 135Watts in parallel with a Blue Sky 3024 MPPT controller.
I now have to go back to work for 5 weeks, which means boat will be unattended for that period.
When I first connected the panels, pleased to see an output of 6 amps on a completely overcast day, sun low in the sky.
The controller is set to an acceptance time period of 4 hours, and the Float Transition current is left at the factory default of 1.5amps per 100 amps.
If I understand the operating manual correctly, this means that the controller will remain at the acceptance voltage for a minimum of 4 hours each day.
Question, is this OK for the batteries which are not being used, or should I drop the acceptance time down to say 1 hour, while I am away.

[noelex 77]

A lot depends on the loads left on overnight and the type of batteries.

If the loads are very minimal it generally a good idea to modify the charging parameters when the boat is left.

Typically I would drop the absorption voltage and float voltage to a low level (say 0.2-0.4v less) and reduce the absorption time to only 10 mins or so.

The other option is to disable the absorption completely.

The third option is disable the absorption , but set a low "equalisation" cycle. Set this at the absorption voltage to come on once a week for half an hour. The batteries will stay at a float voltage, but once a week be raised to absorption voltage.

I think these three options are all OK. If you at least think about problem and adjust the parameters you are ahead of most. Fully adjustable charging parameters on the controller are a big help.

If you have some loads like a fridge its worth watching the system running over a few cycles with similar conditions and selecting an appropriate absorption time.

[nigel1]

Thanks, there will be no loads on the batteries, so I'll drop the absorption time to around 10 mins and drop the voltages.

[twistedtree]

All the chargers I'm familiar with transition to float when the timer expires OR when the charge current drops to whatever threshold has been set. In other words, meeting either criteria will cause the transition to float. So on fully charged batteries, it's unlikely your absorb time will be anywhere near 4 hours. The timer is really there to be sure the charger doesn't stay in absorb forever when you have a load current that's fooling the charger into thinking the battery is still taking current.

[sailinglegend]

Originally Posted by nigel1

....The controller is set to an acceptance time period of 4 hours, and the Float Transition current is left at the factory default of 1.5amps per 100 amps.
If I understand the operating manual correctly......

If I understand the operating manual correctly it clearly says acceptance time OR battery charge current. BUT you need the optional IPN-ProRemote display and the shunt to be able to measure the current actual going into the battery.

This is a great feature not found on many controllers, and it does also provide a Battery Monitor function.

Every controller should have the ability to adjust the basic charge parameters to match the boat. Advanced features can be changed on Morningstar controllers with a serial interface and a PC.

[noelex 77]

The most accurate way to terminate the absorption charge is to measure the current going into the batteries. Sometimes called the battery return current. This is more accurate than a simple timer mechanism and if your regulator will do this it will automatically adjust the absorption time.
As you note it normally requires a separate shunt, or communication with the battery monitor.

Some solar regulators use a default system of just using the solar panel output and assuming this battery return. Most of the time this is useless, but if there is zero load (when the boat is not being used) it will function correctly.
Some of the blue sky regulators will do this. I have never seen it function properly (because there is a load on the boats I see), but it should work in storage mode and reduce the need to adjust the absorption time in storage.

I would still slightly reduce the absorption and float voltage.

[nigel1]

I did decide to fit the IPN Pro-Remote for the reason of being able to change the charging parameters, I also fitted the shunt so it works as a monitor.
This is what the IPN manual has to say
Float Transition Current
“Time in Acceptance” is an accepted method to determine when the battery is fully charged if net charge current is unknown. A preferred method provided by the IPN-ProRemote is to use net battery charge current matched to battery size in amp-hours. With the IPN-ProRemote the charge controller will consider the
battery fully charged and to switch to Float if net battery current drops below the Float Transition Current setting while the battery is at the Acceptance voltage setpoint. The factory default Float Transition Current setting (Float Current in the Battery Charge Parameters menu) of 1.5 amps per 100 amp-hours of battery
capacity is suitable for most batteries. With the factory default Battery Amp-Hour setting of 220 amp-hours, the battery would be considered fully charged when net
battery charge current decreases to less than 3.3 amps while at the Acceptance voltage setpoint.
To assure that net charge current is what determines when the battery is full, Charge Time should be increased to approximately 4 hours. This is so that if battery current is unable to decrease to the Float Transition Current due to battery age or damage, charge will terminate after a reasonable time period.

OK, can see that the controller should drop into float mode when the return amps drop to the transition set point, but just to be on the safe side, and with regard to the warning about battery age or damage, I still think it would be best to reduce the absorption time to minimumwhile the boat is unattended for such a long period.

[sailinglegend]

Originally Posted by nigel1

.......I still think it would be best to reduce the absorption time to minimumwhile the boat is unattended for such a long period.

I do this with my Victron shorepower charger and can save the settings and reload the original when I return to the boat.

[noelex 77]

If the battery return amps termination of the absorption cycle is working you should be able to see the effect on the reported parameters.
On my Outback system for example I can see the absorption time. Sometimes this can be a short as 10 mins, if the batteries have been sitting just under the absorption voltage for a long time.

[twistedtree]

Originally Posted by noelex 77

If the battery return amps termination of the absorption cycle is working you should be able to see the effect on the reported parameters.
On my Outback system for example I can see the absorption time. Sometimes this can be a short as 10 mins, if the batteries have been sitting just under the absorption voltage for a long time.

I think Outback does it all based on time, but they vary the time based on how long the bulk phase takes. The longer the batteries are in bulk, the long the absorb is. I don't know what the exact formula is, but that's at least how their solar charge controller works.

[noelex 77]

Originally Posted by twistedtree

I think Outback does it all based on time, but they vary the time based on how long the bulk phase takes. The longer the batteries are in bulk, the long the absorb is. I don't know what the exact formula is, but that's at least how their solar charge controller works.

The outback with the mate uses battery return Amps to normally terminate the absorption stage. These setting are fully adjustable with both return amps and a variable delay where the return amps have to maintained for a set a set period of time before the absorption phase terminates. Alternatively it can set up to terminate at a set absorption time ( but this is inferior to looking at the return amps).

Without the Mate the battery return amps are not computed so it uses a simpler absorption time, but this time is adjusted if the battery voltage falls lengthening the absorption time if the battery voltage drops ( below 12.4 it starts counting backwards, below 12.0 it counts backwards twice the normal rate). This helps adjust the absorption time, but using the return amps is far more accurate.

[Sumner]

We have our Mac setting out side year in and year out with the Blue Sky 2512 MPPT controller on it....



Macgregor 26S Outside Mods page 33

...with 200 watts of solar going to 2 12 volt batteries in parallel. I check it every couple months are so and when ever I do it is in float according the the LED on the controller and usually about 12.9 to 13.1 on the volt meter and the amp meter is reading .1 amp (as low as it goes).

I personally don't think you have a problem and would just let it go. On the Endeavour we have a 3024 connected to 480 watts...



Endeavour 37 Electrical Mods Index


...when all of the panels are up but....



.... right now just have one 80 watt panel up (in the area of the arrow above) and the rest are taken down just encase a hurricane goes by when we aren't there.

Sum

[twistedtree]

Originally Posted by noelex 77

The outback with the mate uses battery return Amps to normally terminate the absorption stage. These setting are fully adjustable with both return amps and a variable delay where the return amps have to maintained for a set a set period of time before the absorption phase terminates. Alternatively it can set up to terminate at a set absorption time ( but this is inferior to looking at the return amps).

Without the Mate the battery return amps are not computed so it uses a simpler absorption time, but this time is adjusted if the battery voltage falls lengthening the absorption time if the battery voltage drops ( below 12.4 it starts counting backwards, below 12.0 it counts backwards twice the normal rate). This helps adjust the absorption time, but using the return amps is far more accurate.

I'm a little confused about the with/without mate part. I'm looking back at my MX60 docs and do indeed see the ability to terminate absorb based on charge current. But that appears to be available without the Mate as well?

And in both cases, it looks like the current is the charge output of the MX60, which of course differs from the actual battery return current except when there are no loads or other charge sources. Or does Outback now provide a way feed the actual battery return current back to the MX?

It's also possible (probable) that my equipment is not the latest.

[noelex 77]

Originally Posted by twistedtree

I'm a little confused about the with/without mate part. I'm looking back at my MX60 docs and do indeed see the ability to terminate absorb based on charge current. But that appears to be available without the Mate as well?

And in both cases, it looks like the current is the charge output of the MX60, which of course differs from the actual battery return current except when there are no loads or other charge sources. Or does Outback now provide a way feed the actual battery return current back to the MX?

It's also possible (probable) that my equipment is not the latest.

To measure the battery return amps properly you need a shunt close to the battery.
The mate will allow up to three shunts so it will give a separate read out of say:

Solar panel output
Load draw
Net current into the battery
Wind generator output

All very useful information, particularly as you can also get an AHr read out for all the inputs/ outputs.

Without the mate the MX-60 has no idea what the load current is so cannot properly use battery return amps to terminate the absorption phase.

Battery return amps are very useful on a solar system on a boat. Like many boat solar systems it is common for the load to be varied to Prevent reaching the absorption set point and wasting power. So the batteries can be almost charged to the level they should be dropped back to float with very little absorption time.

For example
Today my. System reached regulation voltage about 11am. So I turned on the watermaker. With the draw of the watermaker the voltage has dropped back to 14.0v, with still a few amps going into the battery. The voltage will increase as the sun climbs. At the end of the 2-3 hour watermaker run the batteries will have been held just below the absorption voltage for 2-3 hours.
At the finish of the watermaker run a controller without battery return amps would hold the batteries at the absorption voltage for the absorption time, typically 2-3 hours. This would overcharge the batteries.
Battery return amps enables the controller to recognise that that the batteries are much more fully charged than the low, or nil absorption time would suggest.
It will (correctly) drop the batteries back to float after a very short (or nil) absorption time.

The equipment to do this is expensive, but its worth considering on larger boats where the saving on battery costs help defray the purchase cost.
In addition the more precise termination of the absorption phase means that more aggressive voltages and longer absorption times can be used, charging the batteries quicker.
The complete system reporting of all inputs and outputs is also nice to have.

[twistedtree]

Don't you need the Flexnet DC as well.