Charging batteries using generator & MPPT charge controller

wayneworkman2012

Morning all,

I have an MPPT charge controller rated for 40A, and can take an input of 12 or 24v, and output 12 or 24v. My battery bank is 600A, it's a cluster of 6 100A batteries in parallel.

I've got this 1200W generator that has both AC and DC outputs on it, and it came with this thin little cable for the DC outlet. One end is sort of like a standard AC plug you'd put into an AC outlet but the prongs are not parallel, they are a little offset (to keep people from plugging it into the wall I presume). The other end are just spring-loaded battery connectors.

The DC output says 12v 10A on it's label.

What I want to try is cutting off the spring loaded connectors, and soldering on a pair of MC4 connectors so I can directly hookup the generator's DC output to the input of my MPPT charge controller. I figure the charge controller can handle the 10 amps since it's rated for 40, and that the MPPT charge controller would actually do a much better job at charging the batteries since it can deliver exactly the right voltage the batteries need as they charge up.

Is this ok to do?

Thanks,
Wayne

mcgivor

Don't do it.! That is not the intended purpose of the DC output, enough said...... there are reasons, not worth explaining, unless you really want to know why not.

Estragon

Aside from the problems I suspect Mcgivor is thinking of, the 12v output is likely too low for an mppt controller to charge a 12v battery. A nominal 12v solar panel will put out ~18v.

The vast majority of controllers buck a higher voltage source down to a lower battery charging voltage. There are a few that are designed to boost voltage, but they're pretty rare. Even if it could work, 10a isn't going to do much for a 600ah bank anyway.

mvas

@wayneworkman2012,
Since you took the time to ask, then I will take the time to answer.

The problem is...
The Max Power Point (MPPT) logic that is built in to the Charge Controller.
Let's assume the Charge controller starts at 1 amp x 12 volts = 12 Watts.
Then it tries   2 amps x 12 volts =   24 watts - is more watts!  So, keep increasing amps ...
Then it tries   3 amps x 12 volts =   36 watts - is more watts!  So, keep increasing amps ...
Then it tries   4 amps x 12 volts =   48 watts - is more watts!  So, keep increasing amps ...
Then it tries   5 amps x 12 volts =   60 watts - is more watts!  So, keep increasing amps ...
Then it tries   6 amps x 12 volts =   72 watts - is more watts!  So, keep increasing amps ...
Then it tries   7 amps x 12 volts =   84 watts - is more watts!  So, keep increasing amps ...
Then it tries   8 amps x 12 volts =   96 watts - is more watts!  So, keep increasing amps ...
Then it tries   9 amps x 12 volts = 108 watts - is more watts!  So, keep increasing amps ...
Then it tries 10 amps x 12 volts = 120 watts - is more watts!  So, keep increasing amps ...
Then it tries 11 amps x 12 volts = 132 watts  and then POP, the 10 Amp breaker blows.
The Charge Controller was "climbing the hill" looking for the Max Power Point.
But Max Power always occurs just when the breaker pops.

PV Panel array - The Voltage will fold-back (decrease) as you increase amps, creating a Max Power Point.
Generator - The voltage does not fold-back (decrease) to any significant degree, to cause a Peak Power Point.
So the breaker always blows.

Solution #1:
=========
Get an inexpensive 120V AC to 10 Amp 2 or 3 stage charger and plug it in to the generator's AC outlet.
You can now Bulk / Absorb charge your Battery Bank.

Solution #2:
=========
Get a 15 amp DC-to-DC Boost inverter.
Set it to 14.8 Volts MAX and 9.5 Amps MAX.
And connect it between the Generator 12 Volts and the Battery Bank.
Bulk Mode = Charge at constant 9.5 AMPS, until voltage rises to 14.8 Volts
Absorb Mode = Charge at constant Voltage at 14.8 VOLTS, while Amps drop towards 0 Amps.
A device something like this one ...
http://www.ebay.com/itm/DROK-Numerical-Control-Regulator-DC-8-60V-to-10-120V-15A-Boost-Converter-/381777997216

nsxnitro

> @mvas said:
> @wayneworkman2012,
> Since you took the time to ask, then I will take the time to answer.
>
> The problem is...
> The Max Power Point (MPPT) logic that is built in to the Charge Controller.
> Let's assume the Charge controller starts at 1 amp x 12 volts = 12 Watts.
> Then it tries   2 amps x 12 volts =   24 watts - is more watts!  So, keep increasing amps ...
> Then it tries   3 amps x 12 volts =   36 watts - is more watts!  So, keep increasing amps ...
> Then it tries   4 amps x 12 volts =   48 watts - is more watts!  So, keep increasing amps ...
> Then it tries   5 amps x 12 volts =   60 watts - is more watts!  So, keep increasing amps ...
> Then it tries   6 amps x 12 volts =   72 watts - is more watts!  So, keep increasing amps ...
> Then it tries   7 amps x 12 volts =   84 watts - is more watts!  So, keep increasing amps ...
> Then it tries   8 amps x 12 volts =   96 watts - is more watts!  So, keep increasing amps ...
> Then it tries   9 amps x 12 volts = 108 watts - is more watts!  So, keep increasing amps ...
> Then it tries 10 amps x 12 volts = 120 watts - is more watts!  So, keep increasing amps ...
> Then it tries 11 amps x 12 volts = 132 watts  and then POP, the 10 Amp breaker blows.
> The Charge Controller was "climbing the hill" looking for the Max Power Point.
> But Max Power always occurs just when the breaker pops.
>
> PV Panel array - The Voltage will fold-back (decrease) as you increase amps, creating a Max Power Point.
> Generator - The voltage does not fold-back (decrease) to any significant degree, to cause a Peak Power Point.
> So the breaker always blows.
>
> Solution #1:
> =========
> Get an inexpensive 120V AC to 10 Amp 2 or 3 stage charger and plug it in to the generator's AC outlet.
> You can now Bulk / Absorb charge your Battery Bank.
>
> Solution #2:
> =========
> Get a 15 amp DC-to-DC Boost inverter.
> Set it to 14.8 Volts MAX and 9.5 Amps MAX.
> And connect it between the Generator 12 Volts and the Battery Bank.
> Bulk Mode = Charge at constant 9.5 AMPS, until voltage rises to 14.8 Volts
> Absorb Mode = Charge at constant Voltage at 14.8 VOLTS, while Amps drop towards 0 Amps.
> A device something like this one ...
> http://www.ebay.com/itm/DROK-Numerical-Control-Regulator-DC-8-60V-to-10-120V-15A-Boost-Converter-/381777997216
.....
What if i have 28v dc generator at 53amps continues duty. Can I wire thru mppt charger? If yes, what would be the best mppt charger for this dc generator?
Thank you

mike95490

nsxnitro said:

What if i have 28v dc generator at 53amps continues duty. Can I wire thru mppt charger? If yes, what would be the best mppt charger for this dc generator?
Thank you

Please don't try that.    A generator is a very different power source than PV panels which MPPT charge controllers are designed to work with.

I would use the DC generator to directly charge your 24V battery, that's likely what the generator was designed for. Then you use your DC meters (volt & amp) to monitor the charge and terminate it when the batteries are full. 

If you have a 12V battery, use a PWM controller rated for at least 60A and let it do the work.

nsxnitro

> @mike95490 said:
> nsxnitro said:
>
>
> What if i have 28v dc generator at 53amps continues duty. Can I wire thru mppt charger? If yes, what would be the best mppt charger for this dc generator?
>
> Thank you
>
>
>
>
>
> Please don't try that.    A generator is a very different power source than PV panels which MPPT charge controllers are designed to work with.
>
>
>
>
> I would use the DC generator to directly charge your 24V battery, that's likely what the generator was designed for. Then you use your DC meters (volt & amp) to monitor the charge and terminate it when the batteries are full. 

Question:
I have two types of gen set.
1 is PM generator head enough to pull over 20amps
2 is self excited generator/alternator pulling 28 to 40v at 53amps max.
Both gen sets are pulling by ac vfd controller.
Question is:
On this case, what would it be best options to charge the bank???
Direct charge with voltage controller or pwm/mppt charger.

>
Thanks for the response.
Can I use continues duty solenoid with voltage meter to cut charge at 28.8 and start charge at 23.5? Would that be safer to direct charge? For 24v bank
>
> If you have a 12V battery, use a PWM controller rated for at least 60A and let it do the work.

mike95490

Do not use a MPPT controller with either genset,

I would suggest a 60A PWM controller with either generator, which I understand to be DC generators.

  It is difficult to learn to manage charging with the human being the meter reader and control circuit.

BB.

I am not sure I would use a PWM charge "series type" charge controller between a DC genset and a battery bank.

Generators and alternators are pretty inductive, and a PWM controller can cause some problems with inductive kickback (high voltage spikes) as the PWM cycles on and off.

MPPT might work better--You would be programming like a "wind turbine" system. Some controllers have programmable power curves. Other folks have just put a MPPT controller on the genset (such as a wind or water turbine) and used them as is...

You need to make sure that the "unloaded" output voltage of the DC genset is under the max input voltage of the MPPT charge controller.

And the DC nominal output current is >1.3x the battery bank charging voltage (14.8 volts charging * 1.3 > 19.2 volts) for the MPPT to do anything "useful" (operate in MPPT mode).

You are a bit on your own here... There are so many variables that can hid issues. Perhaps somebody here can give you some more specific help.

-Bill

nsxnitro

Thank you all for responses. Did some research and I'm better off with direct connection charg.
I'm going to us voltage meter with dump load. Also using contenuies duty solenoid.

robjarnoah

I would like to charge a battery bank with solar panels as a primary and with a generator secondary when solar has not fully charged the bank.   How might I go about integrating the two sources and protecting the bank?  Is there a controller available that can do this for me or do I need to engineer something?

BB.

Welcome to the forum Robjarnoah,

I suggest that you create your own discussion (Thread) and we can discuss your needs there...

In general, having two (or more) properly programmed and wired charge controllers (of any type) paralleled on a single battery bank, is usually fine.

What you want to be careful of (for Flooded Lead Acid type batteries)... Heavy charging current (>~13% rate of charge--200 AH bank, >26 amps charging), the batteries can get hot or even overheat... So, a remote battery temperature sensor (available on may solar charge controllers, and some other types of chargers) can be a good thing (hot FLA batteries, charging voltage goes down, can cause charger to charge with more current, and cause a possible meltdown).

But generally, charging even upwards of 20%-25% can be OK if temperature of bank is OK.

And there are other specialized options... For example, the Midnite Classic and smaller MPPT charge controllers have the option to put a current shunt in series with the battery bank... You can program the Midnite system to limit charging current to XX amps... So, if there is a second solar (or genset based) charger, that charge controller monitoring the shunt will cut back its own charging current.

Off course, if you have both solar and genset charging, you would want to turn off (or not run) the genset while there is a bunch of solar charging current.

There are very sophisticated (and not cheap) integrated off grid and backup solar power systems (solar charger, inverter-chargers, generator auto-start, etc.) systems too...

Feel free to create another discussion, tell us a little more about what you desire (and roughly located), what equipment you may already have, your daily loads (Watt*Hours or Amp*Hours @ xx volts), etc.. We really try for a "balanced" system design so that everything plays well together and does not stress or cause early battery bank failure.

-Bill