Advice on supplementary charging capacity from generator

twistedtree

I'm interested in thoughts from others on this.  Our off grid system is all Xantrex/Schneider XW based, vintage 2007.  Two MPPT-60 charge controllers for solar, an XW6048 inverter/charger, a 14kw diesel generator with AGS, and 1300Ah@48V batteries.

When charging from the generator I'd like to get more charge capacity.  The XW6048 puts out 100A, but only loads the generator about 50%.  I'd like to add another 100A or so of charge capacity to work the generator harder and shorten our run times.

One approach would be to install a second XW.  The advantage is that it would integrate nicely with the existing XW, charge in tandem, display on the SCP, and get tallied by the Combox, etc.  But my XW is vintage 2007 and I'm not sure if it will work in tandem with a newer model.  I see there is the XW+ series, and maybe still the plain XWs?  Which would I need to use, and would it have to be an XW6048, or could I use a smaller unit?  I don't need the extra inverter capacity, and having a second one consuming idle power is actually a draw back.

The other approach would be to get a separate charger and set up it's voltages slightly lower than the XW so it helps during bulk, but drops out as the batteries get through absorb and the XW can carry the final charge load.  This is probably cheaper, but lacks all the integration, data collection, and control of using an XW device.

So, what would you do, and why?  And are there other alternatives that might make more sense?

Estragon

Personally, I would go the second route. Current will drop off anyway during absorb so the extra capacity diminishes in utility. Once batteries get to 85-90% I'd shut the genny down and let whatever solar is available (or a small inverter generator) finish up.

twistedtree

Thanks.  Would you do it that way because it's less costly (I'm assuming it will be, but haven't really compared), or because you think it's a better solution to the problem?

I also neglected to mention that whatever solution I pick needs to be completely automated.  But the generator already starts and runs automatically, so I don't think it's a big challenge.  Any charger connected to the gen output will naturally run only when the generator is on.

mike95490

Me?  i'd get the 2nd XW   But first I'd go to a competent dealer and insure that the old model, with fresh firmware, will work with the new model.   And then you also have a backup inverter as a bonus.  Do you have the Combox ?

And on the other hand, it may NOT change your overall genset run time.  Why ?  Jamming a lot of amps into a low battery "works" but it will quickly fill up, and think it's charged, but you are adding more time at the end of the absorb cycle, something called peukert's law.
The faster you go, the less you get.    So it may vary a bit, I find I get a better charge, when it's spread out over time, rather than trying to front load it quickly.
https://en.wikipedia.org/wiki/Peukert's_law

twistedtree

mike95490 said:

Me?  i'd get the 2nd XW   But first I'd go to a competent dealer and insure that the old model, with fresh firmware, will work with the new model.   And then you also have a backup inverter as a bonus.  Do you have the Combox ?

And on the other hand, it may NOT change your overall genset run time.  Why ?  Jamming a lot of amps into a low battery "works" but it will quickly fill up, and think it's charged, but you are adding more time at the end of the absorb cycle, something called peukert's law.
The faster you go, the less you get.    So it may vary a bit, I find I get a better charge, when it's spread out over time, rather than trying to front load it quickly.
https://en.wikipedia.org/wiki/Peukert's_law

I realize the reduction in charge time won't be linear.  But if I can get it from 7hrs down to 5 or so, I'd be happy.

It doesn't look like you can gang XW and XW+ modes together, and on quick inspection it looks like the XW models are out of production.

But I see another alternative.  I could swap the XW6048 for an XW+6848 (or whatever the model number is), and it has a charging capacity of 140A vs my current 100A.  It's not a big a bump as I might like, it's something.  I also looked into 48V chargers a bit and 50A seems to be the max, though I've only done a cursory look.  But power-wise, adding a charger and swapping for an XW+ would yield about the same charge rate.

animatt

Did you ever find a 50a 48v charger? I saw your thread on here from about 5 or 6 years ago.
I do have some standalone 17a 48v chargers. Golf cart battery chargers.  Work great for bulking. Not great for absorbing as voltage rises their electronics cut there output. 

Supposedly they can be feed 120v or 240v.  I have only ever feed them 120v. 

I would be interested in hearing if you found a larger charger.  Only common ones I see are the iota and they are not that big.
Matthew

mike95490

Wow, 7 hours @ 100A to charge a 1300 pack ?   Sounds like you are draining it deeply, or it's not charging right.
What about using a smaller genset, 14Kw is a bit of overkill ?  And a lightly loaded diesel can have problems (the last 2 or 3 hours)

twistedtree

mike95490 said:

Wow, 7 hours @ 100A to charge a 1300 pack ?   Sounds like you are draining it deeply, or it's not charging right.
What about using a smaller genset, 14Kw is a bit of overkill ?  And a lightly loaded diesel can have problems (the last 2 or 3 hours)

Well, per your earlier point, it doesn't run at 100A for the full 7hrs.  At least the last 3 (and probably closer to 4) are absorb and at progressively diminishing current.  Part of the issue are the stupid Surrette batteries that I foolishly bought, but that's a whole other topic.  The generator kicks on at 48V which is 50% DOD.

If doing it again I might go for a smaller generator, but I own it now so it's not going anywhere.  And it's a real solid machine.  But you are right about light loading, and that's part of the motivation for jacking up the charge rate, though it won't help with the final absorb.  Nothing I can do about that other than switch to LiFePO, but that's still a few years off for me, hopefully.

twistedtree

animatt said:

Did you ever find a 50a 48v charger? I saw your thread on here from about 5 or 6 years ago.
I do have some standalone 17a 48v chargers. Golf cart battery chargers.  Work great for bulking. Not great for absorbing as voltage rises their electronics cut there output. 

Supposedly they can be feed 120v or 240v.  I have only ever feed them 120v. 

I would be interested in hearing if you found a larger charger.  Only common ones I see are the iota and they are not that big.
Matthew

That's pretty funny.  I don't come to this site very often and forgot that I had asked about it before.  Both Mastervolt and Victron make 48V/50A 3 stage chargers.  Cost is about $1800, so probably the cheapest way to get more amps.  Switching to an XW+ @ 140A is attractive provided it's physically a drop-in replacement for the XW power panel and wiring box that surrounds it, and provided I can sell or re-purpose the XW.  Adding a second XW could work too assuming I can actually find one, but will cost probably $4500 to $5000 by the time I add breakers, wiring box, etc.  And I kinda like the idea of a backup inverter.  I'm totally dependent on it, and things would get ugly fast if it failed, especially in the winter.

Solar2

If you add a second XW6048 It must be a Xantrex Schneider, not a Xantrex Schneider Conext.
A XW6848 will not talk to your charge controllers.
But either of these options will make little difference with your charge times anyway.

Diesel gensets usually have good turn down as compared to gas and particularly LP engines.
So you probably are not too bad off.
That is, as Mike mentioned, if they don't wet stack on you.
Any diesel made in the last fifty years or so will probably be ok if they are in decent condx.
Use the extra run to do the wash, heat water, heat your house, garage or shop.
Any electricity you can use directly has the advantage of less battery wear.

As for what I would do;
Build my own charger and run it along with or separate from the inverter charger.
I did this before and it worked great.
I have gathered the components for a 150 amp charger.
Now I need to find the time to get it built.

mcgivor

How about getting hold of some large diodes building a bridge rectifier, convert the generator output to DC, feed that into a MPPT CC of sufficient voltage capacity and charge your battery.  You would need to limit the current to the desired level. 

inetdog

mcgivor said:

How about getting hold of some large diodes building a bridge rectifier, convert the generator output to DC, feed that into a MPPT CC of sufficient voltage capacity and charge your battery.  You would need to limit the current to the desired level. 

It is generally a bad idea to run the output of any kind of spinning machine into an MPPT CC which was not designed for that specific purpose. The MPPT algorithm may try to load the output down into overload or be fooled by the inertial effects that let the generator deliver more power in the short term than the engine driving it can sustain.

mcgivor

inetdog said:

mcgivor said:

How about getting hold of some large diodes building a bridge rectifier, convert the generator output to DC, feed that into a MPPT CC of sufficient voltage capacity and charge your battery.  You would need to limit the current to the desired level. 

It is generally a bad idea to run the output of any kind of spinning machine into an MPPT CC which was not designed for that specific purpose. The MPPT algorithm may try to load the output down into overload or be fooled by the inertial effects that let the generator deliver more power in the short term than the engine driving it can sustain.

My thinking was along the lines of using a power supply to feed a MPPT controller, which would take care of the current limiting, along with the question asked in Morningstar's FAQ, the question, can a power supply be used as a source for a charge controller, they state it can be done with their MPPT controllers with no issue. Your point is valid if there is no limiting of current, although it would be unlikely to overload a 14Kw generator, even the grid has a spinning machine and there is even less chance of  bogging  that baby down. 
Perhaps the best alternative would be to increase PV and use it to finish the absorption, since PV prices are currently low.

Dave Angelini

Solar2 said:

If you add a second XW6048 It must be a Xantrex Schneider, not a Xantrex Schneider Conext.
A XW6848 will not talk to your charge controllers.
But either of these options will make little difference with your charge times anyway.

Diesel gensets usually have good turn down as compared to gas and particularly LP engines.
So you probably are not too bad off.
That is, as Mike mentioned, if they don't wet stack on you.
Any diesel made in the last fifty years or so will probably be ok if they are in decent condx.
Use the extra run to do the wash, heat water, heat your house, garage or shop.
Any electricity you can use directly has the advantage of less battery wear.

As for what I would do;
Build my own charger and run it along with or separate from the inverter charger.
I did this before and it worked great.
I have gathered the components for a 150 amp charger.
Now I need to find the time to get it built.

This post has a few errors in it! All XW's and XW+'s are compatible and will talk with all Schneider and Xantrex based XW equipment !
There are few cases in advanced applications (not yours) where firmware needs to be updated. They will write special firmware and have for me.

On a seperate note, one of the best ways I know of to get a new battery bank is what you want to do twisted tree.
If your bank is truly a 1300ah bank at the 20 hour rate, then 10% is the max you want to charge at if you want long battery life.
Even worse is to all of a sudden jump up the amperage on an older bank that has been cycling for years. You should save up some extra money as I have seen this scenario happen to clients several times when I come in late in the picture. Batteries are electromechanical devices and like nice stable treatment for long life.

I think Mike was amazed at how long this is taking you to charge. Me too!  My clients use a 4 or 5 hour absorb and only try to get fully charged once every 10 days or so. They also have 4+ KW of solar and most are 6+ with some tracking for a large bank.

Estragon

My suggestion of adding a charger was based mostly on cost. There's a lot to be said for a backup inverter/charger especially given yours is 10 years old. One of my Outbacks failed last summer and it was sure nice to be able to just switch the master/slave settings and be back in business. It took a few weeks to get replacement boards.

Also agree with others that running the big generator for a long absorb isn't ideal. Can your solar not finish absorb at least once a week or so?

twistedtree

Dave Angelini said:

This post has a few errors in it! All XW's and XW+'s are compatible and will talk with all Schneider and Xantrex based XW equipment !
There are few cases in advanced applications (not yours) where firmware needs to be updated. They will write special firmware and have for me.

On a seperate note, one of the best ways I know of to get a new battery bank is what you want to do twisted tree.
If your bank is truly a 1300ah bank at the 20 hour rate, then 10% is the max you want to charge at if you want long battery life.
Even worse is to all of a sudden jump up the amperage on an older bank that has been cycling for years. You should save up some extra money as I have seen this scenario happen to clients several times when I come in late in the picture. Batteries are electromechanical devices and like nice stable treatment for long life.

I think Mike was amazed at how long this is taking you to charge. Me too!  My clients use a 4 or 5 hour absorb and only try to get fully charged once every 10 days or so. They also have 4+ KW of solar and most are 6+ with some tracking for a large bank.

So could I add an SWP5548 to my system and expect it to work?  The 6048 is running the latest firmware.  The XW+ system design manual says that multi-inverter systems must use identical model inverters.  Are you saying that's incorrect?

I hear you on the 10% charge rate.  But back when I first installed this system, Surrette insisted that I needed a much higher charge rate.

As for how long it takes to charge, I'm not sure what to say.  The batteries are 1350AH@48V (Surrette 4KS25P batteries), so 64kwh capacity.  Now that I have the combox and reasonable logging of power, my generator charge cycles put about 34kwh into the batteries.  That's a little over 50% of the capacity.  The generator kicks on when the bank hits 48V which is about 50% DOD.  So putting 34kwh back into them to reach full charge seems about right to me.  Beyond that, it's all about the acceptance rate of the batteries.  If the batteries accepts the full 100A until fully charged, and assuming an average voltage of 58V during charge, it would take 5.8hrs to charge.  I'm seeing between 6.5 and 7.5hrs, which given absorb time, makes sense to me.

I know a lot of people only use their generator to get through bulk and then shut off.  I've elected to let the generator run all the way through absorb.  It's arguably harder on the generator, but when the generator runs it's because the sun hasn't been out for several days.  In Nov and Dec, this can go on for weeks and weeks, so I've elected to bring the batteries back to full charge.  Aside from this time of year, the generator almost never runs and the solar covers everything.

mike95490

All this leads to the next question, what the heck are your loads that are pulling that much power out of the batteries ?
Resistance heating ?
Just asking questions and trying to figure it out

twistedtree

Daily loads vary between about 4kwh in the summer to 6kw in the winter, and jump to as much as 11kw when the place is being "heavily" used, which means the dishwasher is running more than once a day and/or there is a lot of laundry being done, and lights on all day in the shop, TV and music on, etc..  That's a 250W to 500W average load in the winter.  So when the place is in full swing and the sun isn't shining, we will need a generator charge cycle every 3 days or so.  This is typical over the Thanksgiving and xmas holidays when kids are home, etc.  The design goal of this house was efficiency, but without compromising convenience and comfort.  Heating is propane fired circulating hot water, so electric is required to run the boiler and circulators.  Refrigeration is propane, except we have an electric chest freezer that we turn on over the holidays.  Lighting is mostly LED now, but the shop lights are florescent and do draw some power.  Solar is 3.2kw, and yields about 12kwh on a sunny winter day.  Most of the standby loads get shut off when the house isn't occupied.  There are wall switches that cut power to the stove, microwave, and washer/drier, and entertainment gear.  Water is via gravity feed, so no pumping.  But internet, alarm, security cameras and monitoring system run 24x7x365.

So aside from November and December when consumption is highest and solar production can be zero for days on end, the solar carries the load just fine and the generator only runs to exercise itself.  Since installing the Combox at the beginning of October, the generator has logged 92 hrs.  With an average run time of 7 hrs, that's 13 cycles, or about once a week over the 3 months until now.

All this seems about right to me, but perhaps I'm missing something.  Dave talks about clients with 4-6kw of solar.  I'm operating well below that with no generator 75% of the year.

twistedtree

mike95490 said:

All this leads to the next question, what the heck are your loads that are pulling that much power out of the batteries ?
Resistance heating ?
Just asking questions and trying to figure it out

I occurs to me that part of the confusion may be the time period over which the batteries are drawn down.  The 30kwh consumption is not a daily consumption.  It's an accumulated consumption running just on batteries over 3-5 days when there has been near zero solar production.  Yes, if my daily consumption were 30kwh, I'd have my meter out and be checking loads to find the problem.

Dave Angelini

It is the ability to use less energy in winter that is your weak point in this system in my opinion. Having the extra solar is of course for winter. You do not live in a place that can do without a generator but I know about 40 who do.  It is what you want and so be it.

I do not know what a SWP5548 is. It is true that if you stack inverters they need to be the same model to work AC output together. An XW and an SW (example) can run fine together for charging (DC output)  they just can't run their (AC) outputs to the same load panel at the same time. Many with large banks use 2 inverter/chargers or more and have a spare as not many need more than 6KW of AC output offgrid. I am testing now with a system with XW and XW+ all running together but not stacked.

Battery companies design for lasting the warranty.  Some of what they say is about staying in business and selling more batteries.
The harder you charge above 10% the shorter the life.  Charging at a higher rate after a battery has been broken in and in cycling duty
is detrimental but good for sales.

I do not have a paper XW6048 manual from before 2009 and my oldest manual said 127 amps DC was the charger. Are you sure about the 100adc output? I have a client with a 2006 XW that has never had the firmware changed because there is very little in the offgrid application has changed. Just a widening of AC2 voltage qualification and some 3 phase changes.

One problem I see people do is set the capacity incorrectly in the charger menu. Make sure it is set for 1300 AH so the battery goes to float at 26adc on generator power. Sounds like pretty deep cycles and that is your strategy. I would not suggest to do that.

mike95490

3 days between generator runs (50%) is going to shorten your battery life.   I'd suggest no more than 2 days, and if you know the weather is going to be foul for days, daily runs till it clears and you get solar.    No point in deeply cycling batteries.
And BTW, do you have a backup genset ?
(regarding programming bank size, I have 800ah, but set to 1,000 for much easier math and caculation ramping up charge rate as genset warms up 15% = 15A)

twistedtree

Sorry, I meant XWP, aka XW+.  And you answered the question - thanks.  I can just use a second unit as though it's powering a separate AC load.  So it's good to know I can use a current model unit if I wanted to add charger capacity and still have it accounted for by the Combox.

I checked my XW6048 manual and it lists 127A as the max DC load current, and 100A as the max DC charge current.  Looking at the latest XW6048 manual on the Schneider web site, it lists 160A max load, 100A max charge.

But I suppose it's all moot since you guys are suggesting I leave well enough alone with the charge rate.

Dave Angelini

That is what I would do until you change batteries. I was mixing up the specs so yea leave it alone. The 6848+ I am running is 140A charge rate but, I don't have a generator To test it, I have another XW outputting 240VAC into the + series charger. It all shows up on combox. In really large apps with many XW devices a combox can be a master and drive additional comboxs as slaves.  I will be selling the + in the near future.

 Your prices you quoted for a new inverter sound pretty high BTW.  I assume that you are looking at SG for full and have the correct set-points! Good Luck! 

twistedtree

Yes, set points are all geared to getting SG back to full charge.  That took some tweaking early in the life of the system, but has been stable for some time now.

Mangas

One feature in the programmable auto AGS stop triggers that would I like to see added is a simple stop generator time duration.  Here it is unnecessary to run the Generator all the way to full charge battery voltage before the default max run time shuts the Generator down.  

Normally, our rare low voltage starts occur in early morning and after a couple hours of generator run time we have more than enough sun to finish charging without more generator hours.  Our old Trace's allowed us to set generator run times instead of having to use AGS Stop Absorb, Stop Float or Default Battery full charge stops. But, I understand the battery management reasons for the added AGS parameters.

For low voltage starts, thinking about setting up the AGS' on a Stop V 53 volts which could accommodate late morning solar charging when the genset is no longer needed. After three hours My SOC SGs' were already pretty good and 52 - 53 volts showing on the SPC.


 

Dave Angelini

I would suggest that you use the feedback form from the support section of the Schneider Solar site.
http://solar.schneider-electric.com/feedback/
Good Luck !  You may get them to have an engineer call if you ask!  Looking at the weather in Tucson. 

Mangas

Thanks Dave!

Called and talked to both support and engineering.  They acknowledged my reasons and engineering is giving me a couple of options.

Smiled at your forecast.  Volts and SOC SG look good!