Feed PWM charge controller from DC power supply?

[lkruper]

I have read threads on various sites that discussed using a MPPT charge controller with a DC power supply to charge batteries. It would seem to be a potentially good solution to have equipment with multiple uses. However I read that Midnight Solar does not endorse it and an issue with a "stiffness" in input power.

What about a PWM controller? Chargers with temperature compensation are more expensive but something like Xantrex 12/24/48 40 amp charge controller is $135 on Amazon. It gives the flexibility of charging different battery banks and so meets my goal of buying something that works with 12v and later could work with 24v. I was looking at a DC power supply that can output variable 0-32v @ 0-30a to pair with this. These two should provide equipment that can grow from 12v to 24v. The PWM charge controller can provide the charging automation. There must be something wrong with this... I have a feeling.

[SunEagle]

I have read threads on various sites that discussed using a MPPT charge controller with a DC power supply to charge batteries. It would seem to be a potentially good solution to have equipment with multiple uses. However I read that Midnight Solar does not endorse it and an issue with a "stiffness" in input power.

What about a PWM controller? Chargers with temperature compensation are more expensive but something like Xantrex 12/24/48 40 amp charge controller is $135 on Amazon. It gives the flexibility of charging different battery banks and so meets my goal of buying something that works with 12v and later could work with 24v. I was looking at a DC power supply that can output variable 0-32v @ 0-30a to pair with this. These two should provide equipment that can grow from 12v to 24v. The PWM charge controller can provide the charging automation. There must be something wrong with this... I have a feeling.

Without doing a lot of looking I would say the biggest difference between the Xantrex PWM CC and a MPPT is probably the amount of panel wattage that can be connected to it and the PWM being lower efficient wise.

[Willy T]

I have read threads on various sites that discussed using a MPPT charge controller with a DC power supply to charge batteries. It would seem to be a potentially good solution to have equipment with multiple uses. However I read that Midnight Solar does not endorse it and an issue with a "stiffness" in input power.

What about a PWM controller? Chargers with temperature compensation are more expensive but something like Xantrex 12/24/48 40 amp charge controller is $135 on Amazon. It gives the flexibility of charging different battery banks and so meets my goal of buying something that works with 12v and later could work with 24v. I was looking at a DC power supply that can output variable 0-32v @ 0-30a to pair with this. These two should provide equipment that can grow from 12v to 24v. The PWM charge controller can provide the charging automation. There must be something wrong with this... I have a feeling.

I have a couple C-35's that are in their 5th year. The only issue is the Absorb time is limited to one hour as is the Equalize time by the controller. They both hooked to IOTA converter / charger's with the voltage cranked up to 15.5v and 32v. Never tried a MPPT. Dollar for Dollar it's about a wash over the cost, but they do give you some flexibility and no BS like a smart charger.

[lkruper]

Without doing a lot of looking I would say the biggest difference between the Xantrex PWM CC and a MPPT is probably the amount of panel wattage that can be connected to it and the PWM being lower efficient wise.

I was hoping that the ability to set the DC supply from 0-30v and 0-30a would allow me to find a setting that would be efficient for either 12v or 24v batteries.

[lkruper]

I have a couple C-35's that are in their 5th year. The only issue is the Absorb time is limited to one hour as is the Equalize time by the controller. They both hooked to IOTA converter / charger's with the voltage cranked up to 15.5v and 32v. Never tried a MPPT. Dollar for Dollar it's about a wash over the cost, but they do give you some flexibility and no BS like a smart charger.

That's good news. The only thing I can think of that MPPT would give with an adjustable supply would be to extract maximum amps at both 12v and 24v settings.

[Sunking]

I have read threads on various sites that discussed using a MPPT charge controller with a DC power supply to charge batteries.

If you have a power supply of the proper voltage or even better adjustable, you do not need any controller. But to answer your question a PWM Controller could be inserted between a DC power supply assuming it is of the right voltage of 16 to 18 volts. But it is not needed or required if you can adjust the DC Supply voltage.

[SunEagle]

I was hoping that the ability to set the DC supply from 0-30v and 0-30a would allow me to find a setting that would be efficient for either 12v or 24v batteries.

Maybe, but I wouldn't gamble that just using a DC power supply will be able to properly charge an expensive bank of batteries.

At least with a decent solar CC or battery charger there is software that controls the amount of charging current going into the battery.

[lkruper]

If you have a power supply of the proper voltage or even better adjustable, you do not need any controller. But to answer your question a PWM Controller could be inserted between a DC power supply assuming it is of the right voltage of 16 to 18 volts. But it is not needed or required if you can adjust the DC Supply voltage.

My concern was that my proposed battery bank would be in an unheated basement at 5500 elevation where there can be freezing temperatures. So I could set a voltage for a particular temperature and have things change quickly if I am not there. That is a float scenario for batteries that are backup in nature. One thing I thought of was to charge the batteries when I am there (at least once or twice a month) and then let the batteries sit with no charge until the next visit. I might lose 15% per month charge that way which would be replenished on a monthly or bimonthly basis.

However having a CC with a temperature compensation should take care of that problem for me, at least that is my currently thinking.

[inetdog]

Here is a brief recap of the potential problems with using a battery bank or a DC power supply as the input to a CC. Both PWM and MPPT have potential problems, they are just different problems:

1, PWM: A PWM CC is just a fast electronically controlled switch that effectively connects the source directly to the battery terminals but pulses that connection on and off to get the desired average voltage and average current going to the battery.
A CC which is designed for PV input makes the completely justified assumption that the current from the panels will be limited and so the CC's switching element will not be overloaded and burn up.
In reality the current from the panels is bounded by the Isc of the panels but will actually be a lower value based on the panel current versus voltage curve and the terminal voltage of the battery.
In any case it works fine with PV input.
Now consider what happens when you substitute a higher voltage battery bank or a DC power supply.
When the switching element is on the current will be whatever the battery or supply voltage can drive into the battery via a direct connection. If you have a 48V battery and are trying to charge a 12V battery the current will be so large that it will burn out the switching element in the PWM CC.
If you have a power supply instead and set the voltage low enough that the current through a direct connection is low enough for the CC to handle it OR if the power supply has adjustable current limiting, then you could be OK. But one supply voltage will not work for both 24V and 12V batteries. Again, current limiting on the supply may allow it to work or the supply may simply shut down rather than supplying the limited current at a lower voltage.

2. MPPT: In an MPPT CC there is never a direct connection between source and the battery being charged. Instead the power goes through a DC to DC converter whose input characteristics are controlled by an MPPT algorithm to get maximum power from the panel(s).
One form of algorithm has the CC trying to draw more and more current from the supply until the voltage drops low enough that increasing the current no longer increases the power delivered.
When the source has a I versus V curve like that of a PV panel (or a wind or water turbine), this is a safe process.
If the source is "stiff", meaning that increasing the current has only a small effect on the voltage, the MPPT algorithm could sweep into a condition where too much current is being drawn for the source battery or power supply to be happy or where the CC itself will be damaged by the high current.

Bottom line: You will have better odds of success with an MPPT CC, but pay attention to the manufacturer's recommendations on whether to try it or not.

[lkruper]

Here is a brief recap of the potential problems with using a battery bank or a DC power supply as the input to a CC. Both PWM and MPPT have potential problems, they are just different problems:

1, PWM: A PWM CC is just a fast electronically controlled switch that effectively connects the source directly to the battery terminals but pulses that connection on and off to get the desired average voltage and average current going to the battery.
A CC which is designed for PV input makes the completely justified assumption that the current from the panels will be limited and so the CC's switching element will not be overloaded and burn up.
In reality the current from the panels is bounded by the Isc of the panels but will actually be a lower value based on the panel current versus voltage curve and the terminal voltage of the battery.
In any case it works fine with PV input.
Now consider what happens when you substitute a higher voltage battery bank or a DC power supply.
When the switching element is on the current will be whatever the battery or supply voltage can drive into the battery via a direct connection. If you have a 48V battery and are trying to charge a 12V battery the current will be so large that it will burn out the switching element in the PWM CC.
If you have a power supply instead and set the voltage low enough that the current through a direct connection is low enough for the CC to handle it OR if the power supply has adjustable current limiting, then you could be OK. But one supply voltage will not work for both 24V and 12V batteries. Again, current limiting on the supply may allow it to work or the supply may simply shut down rather than supplying the limited current at a lower voltage.

2. MPPT: In an MPPT CC there is never a direct connection between source and the battery being charged. Instead the power goes through a DC to DC converter whose input characteristics are controlled by an MPPT algorithm to get maximum power from the panel(s).
One form of algorithm has the CC trying to draw more and more current from the supply until the voltage drops low enough that increasing the current no longer increases the power delivered.
When the source has a I versus V curve like that of a PV panel (or a wind or water turbine), this is a safe process.
If the source is "stiff", meaning that increasing the current has only a small effect on the voltage, the MPPT algorithm could sweep into a condition where too much current is being drawn for the source battery or power supply to be happy or where the CC itself will be damaged by the high current.

Bottom line: You will have better odds of success with an MPPT CC, but pay attention to the manufacturer's recommendations on whether to try it or not.

It sounds like the Mastech 30-30 with the built-in Arduino Nano is the way to go if I feel up to the challenge of adding my own temperature sensor to the Nano and making a project of it. In the mean time, I can use it without temp compensation.

[Sunking]

My concern was that my proposed battery bank would be in an unheated basement at 5500 elevation where there can be freezing temperatures. So I could set a voltage for a particular temperature and have things change quickly if I am not there. That is a float scenario for batteries that are backup in nature. One thing I thought of was to charge the batteries when I am there (at least once or twice a month) and then let the batteries sit with no charge until the next visit. I might lose 15% per month charge that way which would be replenished on a monthly or bimonthly basis.However having a CC with a temperature compensation should take care of that problem for me, at least that is my currently thinking.

OK let's see if we can get you lined out. For Winter Storage there are several good options. Without a doubt a DC Power Supply, a good quality supply with adjustable voltage output and current limiting. Essentially any DC Power Supply is a battery charger a Float Charger which by all means is the best charge algorithm for any Pb and even Lithium. It requires two features which most quality Bench Top DC Power Supply has. A means to adjust the voltage with precision in the proper voltage range of interest. A built-in current limit so you cannot over load the power supply. With Current Limit it just folds back the voltage and becomes a Constant Current supply until the battery voltage rises up to charge voltage. At which point current will taper off to ZERO amps if the voltage is set to the correct Float Voltage. At that point the battery is 100% charged up and waiting to go. Leaving it on float keeps the battery 100% SOC. No need to worry much about temperature compensation in float service over the winter. For a 12 volt battery to cover all varieties you are looking for something adjustable 13 to 14 volts, and for 24 volt 26 to 28 volts............................................. .................................................. ............................................... For Float Charger, it does not have to be large assuming the battery is already fully charged up. You can maintain a 250 AH battery with 3 amps and that is a bit of overkill.......................................... .................................................. ................. Another way to maintain a battery over winter is just to fully charge it, and top-off charge at least once a month. Cold is not necessarily bad for batteries. Under storage conditions, batteries should be stored in the cold as it really slows down self discharge and chemical reactions slowing down the hands of time. The only real danger to a battery in storage is getting too hot, or freezing solid and cracking the battery jar. A fully chargged battery can handle -40 F................................................. .................................................. ........................ Even a simple 10 to 20 watt battery panel work. All it needs a simple 3-terminal voltage regulator and a couple of 5-cent resistors can be easily made for less than $5. Anytime the sun shines you have up to a 1-2 amp Float Charger. More than enough to keep a fairly large up to 200 AH topped off all winter.

[lkruper]

OK let's see if we can get you lined out. For Winter Storage there are several good options. Without a doubt a DC Power Supply, a good quality supply with adjustable voltage output and current limiting. Essentially any DC Power Supply is a battery charger a Float Charger which by all means is the best charge algorithm for any Pb and even Lithium. It requires two features which most quality Bench Top DC Power Supply has. A means to adjust the voltage with precision in the proper voltage range of interest. A built-in current limit so you cannot over load the power supply. With Current Limit it just folds back the voltage and becomes a Constant Current supply until the battery voltage rises up to charge voltage. At which point current will taper off to ZERO amps if the voltage is set to the correct Float Voltage. At that point the battery is 100% charged up and waiting to go. Leaving it on float keeps the battery 100% SOC. No need to worry much about temperature compensation in float service over the winter. For a 12 volt battery to cover all varieties you are looking for something adjustable 13 to 14 volts, and for 24 volt 26 to 28 volts............................................. .................................................. ............................................... For Float Charger, it does not have to be large assuming the battery is already fully charged up. You can maintain a 250 AH battery with 3 amps and that is a bit of overkill.......................................... .................................................. ................. Another way to maintain a battery over winter is just to fully charge it, and top-off charge at least once a month. Cold is not necessarily bad for batteries. Under storage conditions, batteries should be stored in the cold as it really slows down self discharge and chemical reactions slowing down the hands of time. The only real danger to a battery in storage is getting too hot, or freezing solid and cracking the battery jar. A fully chargged battery can handle -40 F................................................. .................................................. ........................ Even a simple 10 to 20 watt battery panel work. All it needs a simple 3-terminal voltage regulator and a couple of 5-cent resistors can be easily made for less than $5. Anytime the sun shines you have up to a 1-2 amp Float Charger. More than enough to keep a fairly large up to 200 AH topped off all winter.

Thanks Sunking, I really appreciate it. I was wondering if I could use my 3.5 amp NOCO Genius for something and you have confirmed it. I also have a Sunforce 15 amp panel with a 1 amp charge controller already that I was going to use to play around with. My 2200w inverter generator also puts out 12v 5a unregulated that they say is for charging auto batteries, but I don't think that is going to get me anywhere.

Thanks again

[super o]

Thank you.

[lkruper]

Connect 4 12v chargers to 4 individual batteries in 48v bank?

http://midnitesolar.com/Forum/index.php?topic=1380.msg11159#msg11159

Can this be done while batteries are in series?

[inetdog]

http://midnitesolar.com/Forum/index....11159#msg11159

Can this be done while batteries are in series?

Using two lower voltage chargers, you mean?
Yes, that can be done with the batteries still in series IF the charger outputs are isolated from the incoming power ground and the insulation between the internal electronics and the case can withstand the voltage. For two 12V chargers and a 24V bank I would expect it to be fine. For two 8 12V chargers and a 96V battery bank I would not be as optimistic.

If one side of the charger output is grounded I do not recommend trying to float the whole charger off ground to avoid a short circuit. It is theoretically possible, but a very bad idea.