Can a pwm and a mppt both be connected to the same battery bank?

bgu1982

I'm curious if I can use both a pwm and a mppt controller on a single battery bank at the same time. Will the batteries accept power from both chargers without any problems? The volts should be about equal.
 
  Also, how should I connect the charge controller to the batteries? Should I use O rings an bolt the cables to the batteries? Should I get heavy duty alligator clips and clamp them on the terminals?

BB.

The MPPT controller needs its own solar array/panel set (cannot share with other solar charge controllers). MPPT controllers adjust the current draw from the array to keep Vmp voltage at optimum point. If you have more than one MPPT controller on the array, the controllers will confuse each other and not figure out how to manage Vmp and Imp for optimum harvest.

For PWM controller, you will usually have a separate array for it too... Although, you can share one array with two (or more) PWM controllers (obviously, the other controller(s) will take energy from the array and spread the array's output energy across the several battery banks).

Each charge controller (MPPT or PWM or whatever) should "home run" back to the battery bus/terminals.

If you "daisy chain" the cable run (from controller 1 to controller 2 to battery bus)--The two controllers can "cross talk" and give you less than optimum charging current (the noise from the "other controller(s)" can be an issue).

You will probably find the two controllers will not be "in sync" (bulk, absorb, float) charging cycles--But that is really not an issue. The battery bank will still get properly charged in reasonable amount of time.

In the end, the controller with the highest voltage set (absorb, absorb time, float) point will "win".

-Bill

BB.

I did have a question--What did you mean by "O Rings"? Did you mean crimp lugs on cable with a hole in the end? Bolted with washer and nut? Generally the "right" thing to do.

Alligator clips (including the heavy duty) are generally make very poor/unreliable electrical connections--Especially under heavy current (i.e., using car jumper cables from battery to AC inverter--The AC inverter will usually find it difficult to run at anywhere near rated output power).

I would only use Alligator clips in an emergency--And quickly change over to bolted connections of some sort as soon as you can.

-Bill

bgu1982

Thank you.

bgu1982

One other question. Is it ok to leave the solar charge controller connected to the batteries while I charge the batteries with a gas generator at the same time? Or do I need to disconnect the CC while charging with the gas generator?

BB.

It does depend on lots of things... Type of battery (lead acid, agm, Li Ion, etc.), state of charge, temperature, etc...

We talk about Rate of Charge. Batteries are generally rated at a 20 Hour discharge rate (i.e., the amount of current to discharge the battery from 100% to 0% state of charge, over 20 hours):

• 200 AH battery capacity / 20 Hour rate = 10 amp average load (100% to 0% state of charge)

You may see other rates like 6 hour, 24 hour, 100 Hours, etc... We use the 20 Hour rate as our "standard" for the rules of thumbs around here.

For flooded cell deep cycle lead acid batteries... The "optimum" is around 10-13% rate of charge (i.e., 200 AH * 0.10 charge = 20 Amps charging). You can go as high as 20-25%, but you should have a remote battery temperature sensor (charging batteries get hot--Fast charging also heats them too).

FLA batteries tend to accept high rates of charge, efficiently (not much self heating) when charging at (very roughly) less than 80% rate of charge... Around 80%-90% the battery voltage rises and tends to "self limit" charging current. 90-100% state of charge, batteries are gassing which does create "waste heat" inside the battery, as well as producing hydrogen and oxygen. At 100% State of Charge (typically Equalizing charge", around 5% to 2.5% rate of of charge is the limit, and if EQ'ing for many hours (cells out of balance, some industrial type FLA batteries), even that low of rate of charge can overheat the battery bank.

As long as you don't overheat (or cause heavy gassing--Light fizzing vs a "rolling boil") lead acid batteries are pretty forgiving... For flooded cell, just make sure that the plates are covered (maybe filled 1/2 way with electrolyte/distilled water before charging). If you fill to mark when cold, the electrolyte expands as batteries get hot, and gassing can push the electrolyte out the top of the cells (messy, lost of electrolyte, etc.). So, charging with both solar and genset is usually not a big issue.

Normally for a solar power system...Suggest genset charging in early morning (battery bank less than 80% SoC, before much sun) and charge up to 80-90% SoC (genset charging at or near rated charger current). Loading genset at ~50% or larger (of rated output) is most efficient. And let solar power pickup the charging for late morning/through rest of day.

Standard (gasoline, propane) gensets run about 50% fuel flow from 50% to 0% electrical loading...

For Li Ion batteries... Just make sure that you do not exceed the battery bank's rated charging current (and the battery bank is within the operating temperature range--Li Ion typically do not like near or below freezing temperatures for charging).

-Bill