More charging capacity from generator

[danderer]

Looking for ideas about adding charge capacity.

Existing setup is 1000Ah of AGM as house bank, a Multiplus 3Kw, Cerbo GX, and BVM-702. The engine has a 320A alternator and WS500 regulator.

Usage is about 400 Ah/day.

The current setup works fine most of the time. If going to a dock to plug in the then Mutltiplus handles the charging load fine. If underway the 320A alternator (putting 200A into the house bank) is very satisfactory.

The unsatisfactory case is sitting at anchor for several days, requiring the generator to run 4 hours a day for the Multiplus to replenish the house bank. I'd like to reduce that run time. I've had several thoughts:

1. Get an additional 100A batter charger, on a separate breaker, that I can use in in addition to the Multiplus to charge the batteries. It would only be used in the case where charging is from the generator.

2. Get an additional Multiplus and parallel it with the existing. While that sounds attractive I see problems: I don't have the space to co-locate it with the existing unit so the cable runs will be significantly different, the cable requirements are honking big, I'd have to upgrade AC cabling and breakers, and I've read of problems getting parallel units to function correctly if they are from different production runs and/or firmware. I also don't need the additional inverting capacity.

3. Get an additional Multiplus and set it to charge-only mode. Do NOT parallel it with the existing unit. It would be on a separate breaker, used as an additional charge source only. It would not need to be co-located with the existing Multiplus and the cabling requirements would be easier to manage. Importantly it would be available as a spare should the primary unit fail - just swap out the primary and swap in the secondary. (The inverter is a critical system for us and currently there is no backup other than running the generator.) The price difference between a 2nd Multiplus and a quality 100A charger seems pretty small.

I'm leaning towards #3 at the moment. Thoughts? Problems I've overlooked?

Oh, as to some obvious answers:
- No good space for a solar installation to make a meaningful difference.
- I don't see lithium as a magic bullet. My limitation isn't charge-acceptance, it is charge-generation. When using the generator I don't drive the batteries to float, just into the acceptance range.

 

[tiltrider1]

I think you have a good grasp of the situation. I have a backup charger that helps charge my 1400 amp/hr bank. It is also there Incase I need to replace my inverter/charger.

 

[O C Diver]

Have another option for you.
My dock power was out last winter from hurricane Ian. While running the generator to charge the batteries through the inverter's battery charger was an option, doing the bulk portion through the Leece Neville 220 amp second alternator was almost twice as fast. Further, it makes hot water if you have a heat exchanger in your water heater.

BTW, if you have a 320 amp alternator, why is it throttled back to 200 amps?

Ted

 

[Nick F]

Have another option for you.


BTW, if you have a 320 amp alternator, why is it throttled back to 200 amps?

Ted

200 amps would be C/5 (charging at the 5 hour rate), which seems to be in line with FLA good practice.

 

[Nick F]

My limitation isn't charge-acceptance, it is charge-generation. When using the generator I don't drive the batteries to float, just into the acceptance range.

Following with interest. I have the same problem.

 

[danderer]

Have another option for you.

Good thoughts.

The 320A alternator is throttled to put 200A into the batteries (.2c which Rolls says is the preferred charge rate). It also puts out about another 50A handling the house loads when running. So around 250A total. I could push it a bit higher but don't feel a real need to.

In the situation you describe - where power is unavailable for an unknown but finite period - I like your solution. But I don't want to put the additional hours on the main engine on an ongoing basis.

 

[rslifkin]

If you don't want to either double up the Multiplus (in parallel) or upgrade to the 5kva Quattro (gives a 200A charger) then I'd be inclined to just add a separate charger to get more amps in during the bulk phase.

Another option would be to add some solar on top of the pilothouse. Even if it's not enough to keep up with your usage it'll still reduce the amount of power you have to get into the batteries every day with the generator.

 

[O C Diver]

200 amps would be C/5 (charging at the 5 hour rate), which seems to be in line with FLA good practice.

I would verify the charge rate with the battery manufacturer for his AGMs. My Firefly batteries will handle 50% of battery rating during the bulk phase, although they rarely see 40%.

Edit: See that the OP has verified maximum charge rate.

Ted

 

[rslifkin]

On the charge rate thing, the Rolls AGMs are made by Fullriver. I've found with my Fullriver AGMs that they'll happily accept higher charge rates, but once you get above 0.2C, higher charge rates start to heat the batteries up significantly. Up to about 0.15C they stay pretty cool. At 0.2C there's some temperature increase. Push it a bit further and they start to get rather hot (hot enough that my Multiplus stopped charging and the solar dropped to float because of high battery temp). So sticking to 0.2C is probably a wise choice.

 

[twistedtree]

Keep in mind that there is a diminishing return from adding more charge current with lead batteries. They will accept the current, but the increased current will drive the batteries to their bulk/absorb voltage earlier in the charge process, then acceptance will diminish. In a nutshell, you shorten bulk, but lengthen absorb. Unless you are at really high charge rates the cumulative charge time will still shorten, but not by as much as you would expect from the increased charge rate.

What’s the rating on your multi? 100A? 120A? If 200A from you alternator is working well, then matching that with chargers from the generator probably makes sense and is good move. I would probably just as a charger which I think was your option 1, but option 3 does give you a cold standby, so I understand the appeal. It’s just a lot more work to install.

As you describe your operation, I would be more concerned about how frequently you return the batteries to really full charge.

You said you are not ready for LFP, but I will mention that with them you really do get full utilization of increased charge rates, and don’t have the absorb cycle to worry about, either with respect to increased generator run time, nor with respect to decreased battery life.

 

[danderer]

Keep in mind that there is a diminishing return from adding more charge current with lead batteries.

Yup. My goal here is not to drive the batteries to float but just into absorption and maybe a little beyond. What I think will work best is cycling the batteries between 40% and 80% (roughly).

Yes, I know the 50% 'rule' but I'm willing to trade off some cycles for better livability.

What’s the rating on your multi? 100A? 120A? If 200A from you alternator is working well, then matching that with chargers from the generator probably makes sense and is good move. I would probably just as a charger which I think was your option 1, but option 3 does give you a cold standby, so I understand the appeal. It’s just a lot more work to install.

120A, less loads so around 100A into the batteries.

I don't see option 3 as more work. I'd install the 2nd Multiplus just the same as I would a charger: 120VAC in, 12V out with cabling sized for 120A.

As you describe your operation, I would be more concerned about how frequently you return the batteries to really full charge.

A good point. The capability I'm shooting for here applies only on days where:

- We're on the hook for multiple days in a row, and
- Haven't run the main engine to move to a new location.

So perhaps 30 days a year. All other days the batteries will come up to 100%, either from traveling on the main or being plugged in dockside.

..and having said that I wonder how much worry I should invest for better performance for 30 days a year. Still, I like the idea of having a backup should the inverter go TU.

 

[kchace]

It seems to me that charging at 100a into a 1000AH bank you are leaving a lot on the table. That is only .1C and AGMs can usually be charged at .2-.25C. This also explains your needing to run the generator for 4hrs a day to replenish the 400AH usage. I would suggest adding another 100A charge capability. I think you’ll get the most bang for the buck there.

Ken

 

[twistedtree]

Yup. My goal here is not to drive the batteries to float but just into absorption and maybe a little beyond. What I think will work best is cycling the batteries between 40% and 80% (roughly).



Yes, I know the 50% 'rule' but I'm willing to trade off some cycles for better livability.







120A, less loads so around 100A into the batteries.



I don't see option 3 as more work. I'd install the 2nd Multiplus just the same as I would a charger: 120VAC in, 12V out with cabling sized for 120A.







A good point. The capability I'm shooting for here applies only on days where:



- We're on the hook for multiple days in a row, and

- Haven't run the main engine to move to a new location.



So perhaps 30 days a year. All other days the batteries will come up to 100%, either from traveling on the main or being plugged in dockside.



..and having said that I wonder how much worry I should invest for better performance for 30 days a year. Still, I like the idea of having a backup should the inverter go TU.

Sounds like you have good handle on the project and associated tradeoffs. I think either source of additional charging will serve you well.

 

[Simi 60]

I might have missed it but can your Genset handle the extra load of additional chargers?

 

[danderer]

I might have missed it but can your Genset handle the extra load of additional chargers?

Yup. 12kw. Can’t run EVERYTHING at once even now but plenty of overhead for this specific need.

 

[Mambo42]

Is installing some solar panels an option ? I understand you are in Delaware, but I have no idea what the weather is over there.
If you would have around 2 Kwp of solar that would mean about 1000 W per hour during sunny days, which is roughly 70 Amps of charge (at 12 V) per hour, which would solve your problem. After all you need about 400 Amps and just on solar alone you would be able to get that in about 6 hours.
I have 3.2 Kwp in solar and during the summer I regularly have 2.5 Kw or 100 Amps (at 24 V) per hour (between 10 AM and 5 PM, before and after that I am around 1400 - 1500 W, or 60 Amps per hour). We do spent a lot of time on anchor and even now on the dry in the marina we don't use shore power at all.
I saw the silhouette of your boat and you to have enough space to add at least 1.6 Kwp or 2 Kwp of solar, so it might be an idea. A few MPPT controllers and that is it.

Adding another multiplus is an option, but if your batteries are already in the absorption phase then it is not going to help you. Only in bulk it can help you. So I agree with rslifkin to change into a Quattro. Then you will have 200 Amps charge available and on top of that 1 Quattro uses less than 2 Multiplusses.

A last solution, however a costly one, is to change to Lithium. They will charge at full rate until 100 % and then switch off, so with a 200 A alternator you would have them full in 2 hours.

 

[Nick F]

Redundancy - add a battery charger. Preferably one with no electronics.

 

[Jeff F]

Another option would be to add some solar on top of the pilothouse. Even if it's not enough to keep up with your usage it'll still reduce the amount of power you have to get into the batteries every day with the generator.

Agreed. I have 700w installed on my PH and get 3+ kwh per day in fair summer weather. That's 60% of your daily usage.

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[ksanders]

you face a couple of challenges

I run a pair of Victron multiplus units in parallel and the system provides everything I want.

that is a near perfect scenario.

You have redundancy but remember that is one unit faults out you might have to connect a computer and reconfigure for stand alone mode.

If you connect a separate multiplus to the same house bank and then connect it to the cerbo, I am not sure how the cerbo will display the data. The good thing is the cerbo is a monitoring device only unless you enable DVCC mode.

If you do that I would probably create a custom charge profile with the changeover voltage a bit lower on one.

 

[jleonard]

I often used an old fashioned sears battery charger to boost my boats capability. I do that in my travel trailer also when needed
Easy simple solution at least for me.

 

[O C Diver]

Danderer, you mentioned this situation was maybe 30 days a year at 4 hours per day. So how much of the 120 hours do you expect to really save, 33% 40 hours? Is this really about generator time or quality of life on the hook (noise). If the latter, maybe the money is better spent quieting the generator.

Ted

 

[Flatswing]

I too consume a little less than 20A each hour on anchor. My system is less sophisticated with 1100 Ahrs of plain old FLA and a single magnum 2812 inv/charger which will put out 125A reliably. I added a Sterling 60A charger and Xantrex 200W flexible solar panel. On anchor in southern sun, can usually achieve 150-155A net while in bulk mode. Beyond that no advantage.
We have to run generator to cook but typically only 2 hrs a day to cycle house bank in the 65-85% range. Often welcome to cool the boat at supper time with AC to fully load the generator , plus reheat hot water. Off anchor, we get to full charge most days.
Of course, the other side of the equation is to work on decreasing ongoing loads while at anchor!

 

[sunchaser]

Aside from the good advice and understanding shown by the OP I’m curious about the house loads. Is there any chance to drop off some daily amps. We found that converting our ice maker to freezer only knocked off close to 100 amps per day.

But, if well maintained that 12.5 kW genset will go for a very long time provided it runs at say an output higher than 4 kW.

Any chance a Li bank could be added with its own charger and used to feed the existing house bank or a large auxiliary chest type freezer you may have onboard?

 

[Bmarler]

I know you took solar off the list due to space, but even some solar can make a substantial difference. I fit 2 385 watt panels to my pilothouse roof. I have an 1125 ah agm bank and typically use around 350 ah per day. In the summer those panels do a great job of keeping me from having to fire up the generator at all.
On really nice days I can reach 100%soc easily.
If it’s really not an option for you, I’d get a stand alone dumb charger to crank out an extra 100 amps or so on those days you need it. Cheap, easy.

 

[Sleeping Bear]

Your genset probably has an alternator which is hardly used, so an automatic charging relay between your genset battery and your house will utilize the alternator on the genset once the genset batt is charged (which is very quick because all it is used for is to start the genset).

Cheap and easy.

 

[O C Diver]

Your genset probably has an alternator which is hardly used, so an automatic charging relay between your genset battery and your house will utilize the alternator on the genset once the genset batt is charged (which is very quick because all it is used for is to start the genset).

Cheap and easy.

Most generators have very small alternators as there charging requirements are quite small. They are usually quite expensive as they aren't produced in large quantities. I'd rather not risk killing a small expensive alternator for minimal charging gain.

Ted

 

[Mambo42]

I saw the profile of your boat and even though you may think you don't have any place for solar panels, you have more than enough real estate to fit an enormous amount of panels.

This is how I solved the same problem

 

[Mambo42]

Your genset probably has an alternator which is hardly used, so an automatic charging relay between your genset battery and your house will utilize the alternator on the genset once the genset batt is charged (which is very quick because all it is used for is to start the genset).

Cheap and easy.

The generator will feed straight into the multiplus and the inverter/charger will use that to run the charger. The multiplus can charge with 100 A, so that is most likely more than the alternator of the generator can do. I would not put a heavier alternator on the generator, they are not made for that.

 

[danderer]

I appreciate the ideas here. Good stuff to chew through.

 

[Southern Boater]

I saw the profile of your boat and even though you may think you don't have any place for solar panels, you have more than enough real estate to fit an enormous amount of panels.

This is how I solved the same problem

When you were originally quoting solar KW on your own boat, I thought that seems a huge array, and where would you fit that……until you posted pics of your arrangement!
You are certainly committed to solar, impressive!