Charging 6 volt batteries in series

[FarBeyondDriven]

Can I use a 12 volt charger for this application? I will be running 2 Trojan T105 225AH batteries. At what amperage should I charge them at? Thanks!

[Naptown]

Yes you can and you should be charging at about 20-23A

[Sunking]

Can I use a 12 volt charger for this application? I will be running 2 Trojan T105 225AH batteries.

Certainly assuming you are wiring them in series to make 12 volts.

At what amperage should I charge them at? Thanks!

Between C/12 (18.75 amps) and C/8 (28.125 amps)

[Beanyboy57]

Certainly assuming you are wiring them in series to make 12 volts.

Between C/12 (18.75 amps) and C/8 (28.125 amps)

If you have high voltage and low amperage coming from your PV array, won't a charge controller regulate it so that the battery is charged correctly? Assuming that the charge controller is programmed to the correct type of battery.

[Sunking]

If you have high voltage and low amperage coming from your PV array, won't a charge controller regulate it so that the battery is charged correctly?

Yes to an extent with respect to voltage will be regulated, but not current. What you are talking about is a MPPT Charge Controller where Output Current = Panel Wattage / Battery voltage. So armed with that info you automatically know that Battery Voltage x Current = Wattage. So armed with that info how much panel wattage does it take to generate a C/10 charge current on a 12 volt 225 AH battery? 12 volts x 22.5 amps = 270 watts.

FWIW none of that applies to a PWM Controller because with any PWM controller Input Current = Output Current. So to generate 22.5 amps with a PWM controller we have to use standard Battery Panels which have a Vmp of 18 volts. So 18 volts x 22.5 amps = 405 watts to do what a 270 watt panel using MPPT.

In either case the charge current is determined by panel wattage.

[Beanyboy57]

Yes to an extent with respect to voltage will be regulated, but not current. What you are talking about is a MPPT Charge Controller where Output Current = Panel Wattage / Battery voltage. So armed with that info you automatically know that Battery Voltage x Current = Wattage. So armed with that info how much panel wattage does it take to generate a C/10 charge current on a 12 volt 225 AH battery? 12 volts x 22.5 amps = 270 watts.


In either case the charge current is determined by panel wattage.

I have 90v x 5amps = 450watts charging a 24volt 225AH battery, controlled by an MPPT 150/70 charge controller. It seems to keep the batteries in excellent condition when tested with a hydrometer and multimeter on each cell. Would it be better to lower the voltage by having a combination of series and parallel panels?

[Sunking]

Would it be better to lower the voltage by having a combination of series and parallel panels?

Beats me without knowing the manufacture and model number. Consult your owners manual as it will tell you (should anyway) the most efficient input voltage to use vs battery voltage. Here is the chart for one of the best Charge Controllers on the market. As you can see 70 volts is the most efficient from 12 volt to 48 volt battery.

[Naptown]

I have 90v x 5amps = 450watts charging a 24volt 225AH battery, controlled by an MPPT 150/70 charge controller. It seems to keep the batteries in excellent condition when tested with a hydrometer and multimeter on each cell. Would it be better to lower the voltage by having a combination of series and parallel panels?

With an MPPT keep your voltage from the panels as high as possible within the range of your controller to minimize voltage drop and this will allow you to keep the wiring as small as possible within the acceptable voltage drop range.

[Beanyboy57]

Beats me without knowing the manufacture and model number. Consult your owners manual as it will tell you (should anyway) the most efficient input voltage to use vs battery voltage.

Victron Energy Blue Solar MPPT 150/70 Charge Controller. I have read the manual, but I am not an electrician and I may be missing something. As far as I could tell, I just needed to program in the battery type and it would do the rest.

[ImpactBattery]

I have 90v x 5amps = 450watts charging a 24volt 225AH battery, controlled by an MPPT 150/70 charge controller. It seems to keep the batteries in excellent condition when tested with a hydrometer and multimeter on each cell. Would it be better to lower the voltage by having a combination of series and parallel panels?

For the T105 batteries I would not want to exceed 45A when charging.

MPPT controllers are very efficient at converting voltages. It would be more efficient the closer the input voltage is to the out voltage required.

[Naptown]

For the T105 batteries I would not want to exceed 45A when charging.

MPPT controllers are very efficient at converting voltages. It would be more efficient the closer the input voltage is to the out voltage required.

Using that logic makes no sense. Why would he want to reduce voltage from the panels to the CC just to get a bit closer to the input voltage on the battery. This rather negates the entire purpose of an MPPT controller and the benefits that come from it.

[ImpactBattery]

Using that logic makes no sense. Why would he want to reduce voltage from the panels to the CC just to get a bit closer to the input voltage on the battery. This rather negates the entire purpose of an MPPT controller and the benefits that come from it.

I am applying my understanding of physics.

Reduce the amount of energy wasted in conversion and save the amount that is useful energy. The closer you can have side A to side B, the more efficient (the least amount of energy wasted) the system.

The panels put out what they put out (from next to nothing voltage to their peak voltage), so it would make more sense to increase the battery storage voltage, if possible to be closer to the peak.

Converting 48V nominal solar power to 12V storage batteries is a waste of energy. It would be better to have a 48V storage. The MPPT will make the adjustment for current drop and voltage drop to increase efficiencies on say, a cloudy day.

They are great devices! But with all that said real world application may dictate the use of wider voltage arrays based on budget or availability.

…to add to the first response of not wanting to exceed 45A for charging, I should have added a more healthy sustained charging amperage would be 20-25A. The batteries could handle up to 45A without damage.

[Naptown]

I am applying my understanding of physics.

Reduce the amount of energy wasted in conversion and save the amount that is useful energy. The closer you can have side A to side B, the more efficient (the least amount of energy wasted) the system.

The panels put out what they put out (from next to nothing voltage to their peak voltage), so it would make more sense to increase the battery storage voltage, if possible to be closer to the peak.

Converting 48V nominal solar power to 12V storage batteries is a waste of energy. It would be better to have a 48V storage. The MPPT will make the adjustment for current drop and voltage drop to increase efficiencies on say, a cloudy day.

They are great devices! But with all that said real world application may dictate the use of wider voltage arrays based on budget or availability.

…to add to the first response of not wanting to exceed 45A for charging, I should have added a more healthy sustained charging amperage would be 20-25A. The batteries could handle up to 45A without damage.

I will let Sunking beat you up on that post. I have to work now.

[Sunking]

I am applying my understanding of physics.

OK you need to go back to school, or slap the crap out of your crappy physics instructor for making you an idiot who taught you garbage. That is why he or she likely teaches and not in the private sector making real money.

You have no idea of how a MPPT or PWM Controller operates.

A PWM controller is a very simple on/off switch where Input Current = Output Current. So take a standard 12 volt 100 watt battery panel the typical specs are Vmp = 18 volts and Imp = 5.55 amps. Connect that panel either directly to a discharged 12 volt battery, or through a PWM controller and you will have 12 volts x 5.55 amps = 67 watts. You just lost 33 watts using a PWM controller. Minimum losses with a PWM controller is 33% period. If you are an idiot and say buy a 100 watt 24 volt battery panel and connect it to a 12 volt battery you have 12 volts x 2.778 amps or 33 watts out of a 100 watt panel.

Now wake up and smell the coffee burning and lets talk about a MPPT controller. Input Current Does Not = Output Current. They are true Power Converters where Input Power = Output Power - Conversion loss of about 3%. Take that same 12 volt 100 watt battery panel and at the input of the controller you get 18 volts @ 5.55 amps, and on the output you get 12 volts @ 8.1 amps or 97 watts.

Lets go one step further with that same MPPT controller. Except this time I want to get rid of using over priced crappy battery panels and use a Grid tied panel 100 watts with 100 Vmp and 1 amp Imp. At the input of the controller I have 100 volts at 1 amp. On the output I have 12 volts @ 8.1 amps or still 97 watts. Not only do I get to use a much less expensive GT panel, but I get to use much smaller less expensive wire with less losses.

Now run they by your understanding of physics and you will quickly realize you do not know much, or what you think you know is wrong. Bet your physics teacher name was Mr Dunno Chit

[Beanyboy57]

Lets go one step further with that same MPPT controller. Except this time I want to get rid of using over priced crappy battery panels and use a Grid tied panel 100 watts with 100 Vmp and 1 amp Imp. At the input of the controller I have 100 volts at 1 amp. On the output I have 12 volts @ 8.1 amps or still 97 watts. Not only do I get to use a much less expensive GT panel, but I get to use much smaller less expensive wire with less losses.

Now run they by your understanding of physics and you will quickly realize you do not know much, or what you think you know is wrong. Bet your physics teacher name was Mr Dunno Chit

Good to see you are back to your normal self Derek!
Couple of points, the manufacturer of my MPPT controller recommends a panel voltage of at least double the battery voltage, in my case that means I need at least 48v for my 24v battery bank.
Secondly what is the difference between "over priced crappy battery panels" and "less expensive GT panels. I have paid a lot of money for my 5 battery panels damn it! Why are GT panels less expensive? Or should that question be placed on another thread?