Using a 28v generator as backup?

[Gray2Hairs]

8 â€" 235 watt 24v panels (1880 watts total)
8 â€" L-16 430 amp-hour 6 volt batteries wired in 2 banks of 4.
1 â€" Midnite Solar Classic Lite charge controller (Up to 2500 watts @ 24 volts)
1 â€" AIMS 5000/10000 watt modified sine wave inverter
1 â€" 1500 watt military communication generator (28 volt)

Normally all is good and I seldom need to fire up the generator.  When I do, it covers the loads and attempts to charge the batteries.  My question is should I put a charge controller between the generator and the batteries?  The reason i ask is that the batteries seem to be charged after running the generator and after a standing period indicate batteries are at 25.2 v.  When loaded, however, the batteries drop quickly.

Can this generator be run to the same charge controller as the PV panels or do I need to install a 2nd controller?

[Westbranch]

Welcome.  first question is about that generator.  IS it putting out 28 volts or is that its rating.

Assuming it is ONLY giving you 28 volts, that is not enough to fully recharge your batteries! You need at least 30 volts to get a full charge, this increased voltage is needed to cover losses in the wiring and the battery.

Right now you are slowly killing those batteries.   A CC will not make up for what you so not have, ie high enough Voltage.   
As a stop gap get a small genset and an automotive 110v charger to top up and then do an EQ on them using PV if you are getting enough sun...

[Gray2Hairs]

I can tune the generator to put out 30 volts, measured at the batteries.  The only time I have needed the power is this past week.  Last night it was putting out 28.8. 

[Westbranch]

That is better... but may not be enough.  what kind of amperage will it develop?  You should be looking for output of  ~ 5% of the amp hr rating of those batteries as a minimum, better up to 10% for a recovery   like you need to perform now as the batteries are showing  a loss in capacity that tells me they are suffering from undercharging..  What does your manufacturer recommend for an EQ voltage?
add: you would be better to do the EQ's on a single string rather than the 2 together, due to imbalance between strings.

[Gray2Hairs]

The max output at 30 volts is 50 amps.  When I have adjusted the amperage a bit higher the 50 amp breaker will trip so it is reaching the max.  I can adjust the amperage from about 30-50.  Once the sun is back the batteries behave as normal. 

[Westbranch]

you really want to have a good 3 stage controller on that output so you can do more than just 'hit the nail with a big hammer', ie you want to control the gen output to what the batteries need. 
A PWM CC would work. 

I hope Ryan jumps in as to how you would be able to use/wire in your Classic correctly.

What are your charge settings on the Classic?

[Gray2Hairs]

Setting are for Flooded 3 - Absorb 30.8, Float 26.8, Equalize 32.  I understand the need for a multi stage charging system and thats where I was heading originally.  I'm just not sure how or what to use and how to connect it.  Just an FYI, all cables are 4/0 copper welding cable and are 4" between batteries and 12" between banks. 6' cables connect the banks to the inverter.  Number 4 copper from the Classic to the batteries is also 6' long..

[Westbranch]

I just had an additional Aha,  have you taken SG readings on your cells?  this may identify if you have a cell or 2 that are weak and need more attention once you do an EQ. 

Remember an EQ is not usually a one time fix, it is an ongoing process to recover ailing cells, so be prepared to do several EQ's.

Simply, as to connections,  you want reverse current protection (fuse or breaker), same as your Classic (should have), between the additional charger or CC and the battery, so a short does not start a fire...

hth


Add here is a schematic from the KID CC for an example of connections, CB's etc. Just visualize this with the PV replaced with a DC gen set and those are your current batteries, this setup would be in parallel to what you already have.

[phxmark]

If the generator has a built-in adjustable regulator and blocking diodes, I would hook directly to the batteries and set it for the float voltage of the batteries.

[Westbranch]

PHX,  I beg to differ.
The gen presently puts out 28V and the batteries are failing , dying an early death and need to be fully charged and then EQ'd. 
Not set at 26.8V so they can die faster.

[Halfcrazy]

The issue I see is that he said he only runs the generator once in a while. So with that in mind I would set the generator to the normal Absorb voltage and run it as needed. It seems a shame to spend money on a Classic (You would need another Classic just for this) just to get the generator to go to float? If the issue is low SG on the Trojans charging the batteries will be the only help so maybe set the Generator to the EQ voltage and do an EQ charge?

How hard is it to change the generators voltage? I could see the value in a classic if the generator was real hard to change its voltages.

[vtmaps]

1 â€" 1500 watt military communication generator (28 volt)

Normally all is good and I seldom need to fire up the generator.  When I do, it covers the loads and attempts to charge the batteries.  My question is should I put a charge controller between the generator and the batteries?  The reason i ask is that the batteries seem to be charged after running the generator and after a standing period indicate batteries are at 25.2 v.  When loaded, however, the batteries drop quickly.

In order to charge a battery, you must have the ability to regulate the voltage and or current flowing into the battery.  You must be able to create different charging stages (e.g. bulk, absorb, float).  Your generator cannot do that.

You have at least four choices. 
1) set the generator to a low, float voltage.  It will never charge the batteries, but it will prevent the battery from being discharged by your loads (as long as the loads do not consume more than the generator can produce).

2) set the generator to a "medium" voltage, something below the gassing voltage.  This will "bulk" up the batteries, but will never fully charge them and will lead to great stratification.  This is what you are doing now with a voltage of 28.   It's not a bad strategy, as long as you understand what you are doing.  Its a safe strategy... will not harm the batteries if you overdo it.  If you can do this in the morning and then let the solar take over and finish bulk and absorb (and the occasional equalization), all will be well.

3) set the generator to a high absorb voltage.  This will charge your batteries very nicely.  During the absorb stage the battery will draw less and less current as it approaches full charge.  Then if the generator is still running the batteries will get hotter and boil away their electrolyte, and if they don't burn the place down you will be able to get salvage price for them.  If you pursue this strategy, you must babysit the batteries and shut down the generator when they are charged.  One caveat:  you don't have temperature compensation.  The proper absorb voltage depends on the temperature of the batteries.  You may have to adjust the voltage seasonally if the batteries are not at the same temp year round.  Automatic temp compensation (as in a battery charger or charge controller) gives a measure of safety against thermal runaway.

4) set the generator to a high absorb voltage as in #3, but automate the regulation.  That's what charge controllers do.  Since you are using a steady generator (rather than variable sun), you have a few simpler options than a charge controller.  e.g. you could use a timer to shut of the generator.  You would have to learn how long to set it (that would depend on the SOC), but if you run the generator in the morning, you could err on the low side and let the solar finish the charge.

Virtually all charging strategies (including the above) require that you know the SOC of your batteries.  How can you possibly tell your equipment what voltages, currents, and times to use, if you, yourself, don't know whether and when the batteries are charged?   You need an hydrometer and a battery monitor to figure out what will work.  This is true for all systems, not just your generator.   Your goal is to get your voltages high enough and for long enough to charge your batteries, but no higher and longer than necessary because high voltages for long times are tough on a battery and cause corrosion of the positive plate.

--vtMaps

[Gray2Hairs]

WOW, thanks for all the dialog.  I have a Morningstar 60 amp MPPT controller that I replaced with the Classic when I added the last 2 PV panels.  It would seem that placing that between the generator and the batteries might help.  Changing the voltage is a manual adjustment as is the amperage on the generator.  The range of adjustment is not great.  So far it has been several months that solar power has been all that is required to keep the batteries charged.  The past week we have had little to no sun causing me to run the generator.  I try not to run it at all.  I also have other 120v gensets that I could use with a 24v charger so perhaps that would be better.  Thanks you for all the input.  It is appreciated.

[vtmaps]

WOW, thanks for all the dialog.  I have a Morningstar 60 amp MPPT controller that I replaced with the Classic when I added the last 2 PV panels.  It would seem that placing that between the generator and the batteries might help. 

I think that could be a bad idea.  The morningstar controller might get bent out of shape trying to find the maximum power point of a generator.  I think it is a bit more appropriate to use a PWM controller, but I'm not sure.  It has been discussed here or at NAWS, but I can't remember all the details... I do remember that it doesn't always end happily.

--vtMaps