running 12vsmart chargers in parallel

[sunnykids]

Here is a question for the auto sparky's or techo's out there

Is it possible to run 2 x 12v smart ( 3 stage ) chargers in parallel ? e.g , can 2 x 40a chargers be run in parallel to provide 80a charge to a battery bank. The advantage being, if one fails, the other is there to provide battery charging ?

[T1 Terry]

The answer is both simple and complicated, the simple one is yes, the complicated bit is getting the whole 80A from both chargers into the batteries. Lead acid batteries have a poor charge acceptance rate, it would require a large capacity battery system with large interconnection links to get all the 80 amps in during the bulk acceptance mode.
If they are both constant current chargers and they had a high cut off voltage the termial voltage will simply climb to that cut off point and the battery would ultimately be damaged.
If it is a constant voltage type charger, once the battery terminal voltage reaches the chargers upper control point the amps or current will be reduced to maintain that voltage, it's an unknown if it would be evenly shared between the chargers, too many varying factors involved, but if one charger stopped, the other would take over to the max ability of it circuitry or to the voltage set point, which ever was the lower current.

If the batteries were lithium ferrous, the limit is around 3C before voltage would be the limiting factor. 3c means 3 x the rated capacity as an amp rating, I.E. 100Ah LiFeP04 battery would accept 300 amps up until it reached roughly 95% charged, again many limiting factors involved that you really don't want to be bored senseless with.
As an example, my 720Ah lithium battery bank will accept 120 amps from the solar and 40 amps from one mains charger and 100 amps from a battery to battery hook up, all at the same time, without the voltage climbing above 13.2v till around 98% state of charge is reached, then the voltage rapidly climbs to the 14v limiting point.

Sorry, it wasn't a simple to answer question

T1 Terry

[possum52]

The answer is both simple and complicated, the simple one is yes, the complicated bit is getting the whole 80A from both chargers into the batteries. Lead acid batteries have a poor charge acceptance rate, it would require a large capacity battery system with large interconnection links to get all the 80 amps in during the bulk acceptance mode.
If they are both constant current chargers and they had a high cut off voltage the termial voltage will simply climb to that cut off point and the battery would ultimately be damaged.
If it is a constant voltage type charger, once the battery terminal voltage reaches the chargers upper control point the amps or current will be reduced to maintain that voltage, it's an unknown if it would be evenly shared between the chargers, too many varying factors involved, but if one charger stopped, the other would take over to the max ability of it circuitry or to the voltage set point, which ever was the lower current.

If the batteries were lithium ferrous, the limit is around 3C before voltage would be the limiting factor. 3c means 3 x the rated capacity as an amp rating, I.E. 100Ah LiFeP04 battery would accept 300 amps up until it reached roughly 95% charged, again many limiting factors involved that you really don't want to be bored senseless with.
As an example, my 720Ah lithium battery bank will accept 120 amps from the solar and 40 amps from one mains charger and 100 amps from a battery to battery hook up, all at the same time, without the voltage climbing above 13.2v till around 98% state of charge is reached, then the voltage rapidly climbs to the 14v limiting point.

Sorry, it wasn't a simple to answer question

T1 Terry

My head just exploded boom

[sunnykids]

Thanks Terry for your detailed answer. I intend to use 4 x 6v x 200ah agm or wet cell batteries, Still undecided. 4 x 200w solar panels running a 24v mppt controller. I would have liked to use a 60a 12v charger when on mains but good multi stage chargers seem to jump in price once they hit the magic 40a limit.
John

[T1 Terry]

I'm not sure if you realise this, but you will not be able to successfully use an MPPT solar regulator and any other charger together if they are both charging at the same time, like the solar and mains or solar and alternator charging at the same time.
This is because the MPPT controller regularly stops charging to measure rested battery voltage, from there it determines what the best combination of volts and amps, from the volts and amps that are coming in from the solar, that will charge the battery the fastest, it also determines when boost charge has finished and float cycle begins. If a second charging source is linked to the battery and charging at the same time it will cause the terminal voltage to be higher than it would be fully rested, the MPPT controller reads this as being closer to fully charged than the battery really is, so it reduces the output amps. After a predetermined period it again stops charging to read the battery voltage, if it hasn't reduced it considers the battery to be charged and drops back to a trickle charge.
No matter what the theory says, it is less efficient to charge 12v battery using 24v panels and an MPPT controller than it is to use a PWM controller and 12v nom. panels. If you plan to combine alternator charging with solar charging, use a PWM controller and 12v nom. panels, you will be much happiers with the end result.

T1 Terry

[sunnykids]

The only charger that will work together with the solar controller, would be a RANOX DC to DC charger with a feed from the vehicle alternator when travelling. The Ranox provides 25a max reducing the current until full charge is reached.

[T1 Terry]

The only charger that will work together with the solar controller, would be a RANOX DC to DC charger with a feed from the vehicle alternator when travelling. The Ranox provides 25a max reducing the current until full charge is reached.

I think you will find an MPPT solar controller will have conflicts when running with the DC to DC charger and simply shut down to a trickle charge. I have tried 5 different brands of MPPT controller on my test battery/solar set up and all of them had the same problem. If I stopped both methods of charging, then restarted the MPPT controller by turning the solar back on, it would start to charge as normal. Then I could turn the PWM charger on, they would run together for maybe 5 mins max, then the MPPT would go into it's measuring routine and shut down to a trickle charge, even if I turned the PWM controller off the MPPT controller would not come back on line till I turned the solar off for 5 mins, it would then reset like it was a new day and away it would go again. It seemed the higher price for the controller the earlier it shut down. None of the PWM controllers acted that way, I also tried with different mains chargers but the reaction was the same.
The PWM controller has a much simpler charging regime, pour in all you can till the preset voltage is reached, then pour in what ever is required to maintain that voltage.

For the money you will spend buying a good MPPT controller to handle 800w of solar (60 amp controller) you could buy a good quality PWM controller with the added shunt etc to make it a battery monitor and still have enough left for a bit more solar if you needed it, the max difference you could gain from using an MPPT controller on an 800w system would be more than covered by an additional 60w panel, it hardly seems worth the effort when you look at like that does it?

T1 Terry

[sunnykids]

The plan was to use 24v solar panels as they seem better value for money. sending down the charge in 24v ( don't need to increase cable sizes ) to the mppt controller and then convert to 12v for the batteries. Can you do that with a PWM controller? If so, which one would you recommend ?

[T1 Terry]

No, the PWM controller needs the voltages to be similar or there is a lot of losses involved, the price difference compared to what you will actually get to the battery between 12v panels and 24v panels via an MPPT controller is an illusion, you will get more from the 12v panel over the days input, any minor saving in panel cost will be more than eaten up by the higher cost of the MPPT controller, on a $$ for $$ comparison, the 12v panels and PWM controller wins hands down. Then the compatibility issues come into it, it's your call but having been through it myself I can only advise you of the likely outcome from a personal experience hands on level.

[John M]

I think you will find an MPPT solar controller will have conflicts when running with the DC to DC charger and simply shut down to a trickle charge.

I had this problem and had to insert a relay in the line between the solar panels and the regulator to isolate the solar regulator, when the motor is running and the Redarc DCBC 1220 charger connected by via the ignition. I my case with both systems connected simultaneously neither system would charge, both systems appeared to be reading the voltage the other and cancelling each other out.