Firefly Battery Update.


Bill Kinney
 


We have had some pretty extensive experience with our Firefly batteries at this point.  We had a couple lumps and bumps in the road early on, but things now seem to have settled in to good smooth operation. One of the unusual things about using a Firefly battery is the procedure Firefly calls a “Restoration charge.” After an extended period of operating at partial state of charge, to restore full capacity the recommendation...



...perform the restoration charge: charge the G31 to 14.4V at 0.2C to 0.5C and continue to charge until the current drops to 0.5 A on the G31  and apply a float charge of 13.5V( for 24 hours. Fully discharge the battery to 10.5V, and then repeat the same charge cycle.

This is also the perfect time to actually measure the capacity of our batteries, and monitor their health since we are discharging them from 100% full to as close to 0% as you can get. For our battery bank we do this by turning on a 1000 Watt space heater, which pulls about 50 Amps out of our 480 Amp-hour battery bank draining them fully in a little under 10 hours.

 

For our 480 Amp-hour battery bank Firefly’s minimum recommended charger capacity is 96 Amps, and a maximum of 240 Amps, with an optimum target of 192 Amps.  Our DC generator puts out 150 Amps, and our shore power inverter/charger does 70 Amps.  

 

In Early October 2020 we installed our current set of Firefly batteries.  After installation, initial charging and testing we did a full ”restoration charge” bringing the batteries from 100% full, down to dead flat, and recharging at 200 Amps

 

Firefly’s current specification sheet for the G31 version of their batteries lists the C10 capacity as 448 Amp-hours.  Our first test in Oct 2020 came in at 454 Amp-hours. It seemed we were off to an excellent start.  Our batteries managed to supply about 1% above rated capacity.

 

In April 21 after 6 months of use, we again ran a full discharge test, and the result was 459 Amp-hours. Even better!  Obviously this was not a trend that could continue for long…

 

In Sep 21 after 10 months another test:  453 Amp-Hours.

 

Jan 22 at 15 months: 448 Amp Hours, right on the original rated nameplate capacity.

 

I do not have any feeling for how precise these numbers are.  Are they +/- 1% or 10%?  No idea.  The measurement is a bit dicey, since I certainly do not have laboratory grade control of the discharge rate.  So I can’t yet say if there is a real trend here or not.  But the (very!) good news for us is after 15 months of constant use our batteries test out right at the original manufacturer’s capacity specification, or a tiny bit better!

 

Considering that an inexpensive set of flooded lead acid batteries would be approaching the end of their useful life at this age, we count this as a total win.  Will these batteries last long enough to justify the additional cost?  Maybe.  Maybe not.  But they are certainly on the right track.

 

For the way we use our boat, the performance of these seems to be an excellent match. 


Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Porter McRoberts
 

Wow. Great Intel Bill. Thank you 

Makes one rethink lithium in light of the insurance issues.   Or at least consider the firefly a greatly improved bridge to wait for insurers to figure out the low risk reality of lithium. 


Appreciated, 
Porter McRoberts 
S/V IBIS A54-152
WhatsApp:+1 754 265 2206
Www.fouribis.net

On Feb 3, 2022, at 2:27 PM, Bill Kinney <cruisingconsulting@...> wrote:




We have had some pretty extensive experience with our Firefly batteries at this point.  We had a couple lumps and bumps in the road early on, but things now seem to have settled in to good smooth operation. One of the unusual things about using a Firefly battery is the procedure Firefly calls a “Restoration charge.” After an extended period of operating at partial state of charge, to restore full capacity the recommendation...



...perform the restoration charge: charge the G31 to 14.4V at 0.2C to 0.5C and continue to charge until the current drops to 0.5 A on the G31  and apply a float charge of 13.5V( for 24 hours. Fully discharge the battery to 10.5V, and then repeat the same charge cycle.

This is also the perfect time to actually measure the capacity of our batteries, and monitor their health since we are discharging them from 100% full to as close to 0% as you can get. For our battery bank we do this by turning on a 1000 Watt space heater, which pulls about 50 Amps out of our 480 Amp-hour battery bank draining them fully in a little under 10 hours.

 

For our 480 Amp-hour battery bank Firefly’s minimum recommended charger capacity is 96 Amps, and a maximum of 240 Amps, with an optimum target of 192 Amps.  Our DC generator puts out 150 Amps, and our shore power inverter/charger does 70 Amps.  

 

In Early October 2020 we installed our current set of Firefly batteries.  After installation, initial charging and testing we did a full ”restoration charge” bringing the batteries from 100% full, down to dead flat, and recharging at 200 Amps

 

Firefly’s current specification sheet for the G31 version of their batteries lists the C10 capacity as 448 Amp-hours.  Our first test in Oct 2020 came in at 454 Amp-hours. It seemed we were off to an excellent start.  Our batteries managed to supply about 1% above rated capacity.

 

In April 21 after 6 months of use, we again ran a full discharge test, and the result was 459 Amp-hours. Even better!  Obviously this was not a trend that could continue for long…

 

In Sep 21 after 10 months another test:  453 Amp-Hours.

 

Jan 22 at 15 months: 448 Amp Hours, right on the original rated nameplate capacity.

 

I do not have any feeling for how precise these numbers are.  Are they +/- 1% or 10%?  No idea.  The measurement is a bit dicey, since I certainly do not have laboratory grade control of the discharge rate.  So I can’t yet say if there is a real trend here or not.  But the (very!) good news for us is after 15 months of constant use our batteries test out right at the original manufacturer’s capacity specification, or a tiny bit better!

 

Considering that an inexpensive set of flooded lead acid batteries would be approaching the end of their useful life at this age, we count this as a total win.  Will these batteries last long enough to justify the additional cost?  Maybe.  Maybe not.  But they are certainly on the right track.

 

For the way we use our boat, the performance of these seems to be an excellent match. 


Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Arno Luijten
 

Hi Bill,

Good to hear you have positive experiences with Firefly. Regrettably mine are not so positive as I had 8 of them in our Amel 54 but they were not up for the task. The voltage was getting below 24 V when the SOC came below 60-65% and we had any kind of load on the system (fridges mainly). In my case the internal resistance of the batteries seemed fairly high as the voltage dropped significant even at loads in the region of 10-25A.
The guys from Firefly sent me a diagram that made it clear to me that these batteries are typically 0.2 V below AGM batteries and any SOC. After some discussion with them they basically told me these batteries were not suitable for my use-case.
So for me this meant an usable capacity of about 120-150 Ah, not great on a power-hungry Amel 54.
So after a year I decided to replace the batteries with 24V lithium units. Safe to say this was a very expensive experience.

Regards,
Arno Luijten
SV Luna,
A54-121


Michael Winand
 

Hi Bill, we have the same batteries, have not yet done the restoration charge, will be soon. 
I have some questions,  did you split the bank into  two, to get a higher charge rate,  also I am looking to turn off the refrigeration to not run them on the low voltage when draining the battery bank?
I have a victron quattro that is a 120amp charger. 
Michael Nebo sm251

On Thu, 3 Feb 2022, 3:42 pm Porter McRoberts via groups.io, <portermcroberts=yahoo.com@groups.io> wrote:
Wow. Great Intel Bill. Thank you 

Makes one rethink lithium in light of the insurance issues.   Or at least consider the firefly a greatly improved bridge to wait for insurers to figure out the low risk reality of lithium. 


Appreciated, 
Porter McRoberts 
S/V IBIS A54-152
WhatsApp:+1 754 265 2206

On Feb 3, 2022, at 2:27 PM, Bill Kinney <cruisingconsulting@...> wrote:




We have had some pretty extensive experience with our Firefly batteries at this point.  We had a couple lumps and bumps in the road early on, but things now seem to have settled in to good smooth operation. One of the unusual things about using a Firefly battery is the procedure Firefly calls a “Restoration charge.” After an extended period of operating at partial state of charge, to restore full capacity the recommendation...



...perform the restoration charge: charge the G31 to 14.4V at 0.2C to 0.5C and continue to charge until the current drops to 0.5 A on the G31  and apply a float charge of 13.5V( for 24 hours. Fully discharge the battery to 10.5V, and then repeat the same charge cycle.

This is also the perfect time to actually measure the capacity of our batteries, and monitor their health since we are discharging them from 100% full to as close to 0% as you can get. For our battery bank we do this by turning on a 1000 Watt space heater, which pulls about 50 Amps out of our 480 Amp-hour battery bank draining them fully in a little under 10 hours.

 

For our 480 Amp-hour battery bank Firefly’s minimum recommended charger capacity is 96 Amps, and a maximum of 240 Amps, with an optimum target of 192 Amps.  Our DC generator puts out 150 Amps, and our shore power inverter/charger does 70 Amps.  

 

In Early October 2020 we installed our current set of Firefly batteries.  After installation, initial charging and testing we did a full ”restoration charge” bringing the batteries from 100% full, down to dead flat, and recharging at 200 Amps

 

Firefly’s current specification sheet for the G31 version of their batteries lists the C10 capacity as 448 Amp-hours.  Our first test in Oct 2020 came in at 454 Amp-hours. It seemed we were off to an excellent start.  Our batteries managed to supply about 1% above rated capacity.

 

In April 21 after 6 months of use, we again ran a full discharge test, and the result was 459 Amp-hours. Even better!  Obviously this was not a trend that could continue for long…

 

In Sep 21 after 10 months another test:  453 Amp-Hours.

 

Jan 22 at 15 months: 448 Amp Hours, right on the original rated nameplate capacity.

 

I do not have any feeling for how precise these numbers are.  Are they +/- 1% or 10%?  No idea.  The measurement is a bit dicey, since I certainly do not have laboratory grade control of the discharge rate.  So I can’t yet say if there is a real trend here or not.  But the (very!) good news for us is after 15 months of constant use our batteries test out right at the original manufacturer’s capacity specification, or a tiny bit better!

 

Considering that an inexpensive set of flooded lead acid batteries would be approaching the end of their useful life at this age, we count this as a total win.  Will these batteries last long enough to justify the additional cost?  Maybe.  Maybe not.  But they are certainly on the right track.

 

For the way we use our boat, the performance of these seems to be an excellent match. 


Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Bill Kinney
 

Arno,

Partly, I am not surprised. While 8 batteries with a total rated capacity of 480 Amp Hours is more than adequate for us, it does seems marginal for the heavier demands of a 54. It just seems an undersized bank.

But... I am very surprised by your comments about voltage levels. It does not at all reflect our experience--and data. Even with a steady 50 Amp discharge rate (roughly a C10 rate) we see voltages stay above 24 volts down to about 50% SOC.  We routinely draw about 10 amps in normal usage have never seen a voltage below 24.5V. We draw down our battery bank every day down something between 131 Amp-hrs and 190 Amp-hrs below full, and the lowest voltage we have ever recorded in normal usage is 24.6V.  That doesn't mean "we never noticed it", it means it never happened, since our system's data is logged every second.  

A voltage of less than 24 Volts at a discharge of 10 amps--to me--indicate something VERY wrong.  I strongly suspect you had a battery in the string with an internal short, or other issue.  I hope you have better luck with the Li system.

Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Bill Kinney
 

Michael,

As one of the "pre-2K" Super Maramus, our battery box only holds 8 G31 batteries, so our bank has a 480 Amp-hour capacity. Our system allows us to run both generator AND shore power chargers, so with shore power available, we can pump 200 Amps into our batteries, which is very close to the optimum 0.4C charge rate recommended, so no need to think about splitting things up.  

For our battery bank a 120 Amp Charger would be right at 0.25C, which Firefly documents indicate is close to, but above, minimally acceptable.  I assume you have the 12 battery box, so your capacity is 720 Amp-hours, and now the 120 Amp charger is 0.17C, below the minimum recommended by Firefly (0.2 C).

My suggestion would be to contact Firefly Tech support. In the manual they suggest they can recommend an alternative procedure if your charging system is limited to less that 0.2C.  I do not know what that procedure is, but I am curious...

I don't bother turning off the refrigeration units during the draw-down.  They turn themselves off near the end of the run when the voltage drops below about 22.5  Doesn't seem to cause an issue.

Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Michael Winand
 

Thanks Bill,  we have a sm2000, early one, eight battery bank. Installation is 3 years  old now. 
I would say the bank has 700 cycles through it.
I am noticing the morning voltage is around 24.3 with the normal loads 10-12amps, and uses 120 amps  overnight.  2 refrigerators and a freezer.  
We normally have to charge in the morning to make breakfast , go to absorption around 90%and let the solar panels do the rest of the day. 
Will see what happens when I get to do the restoration charge cycles. 
Michael Nebo sm251

On Fri, 4 Feb 2022, 3:50 pm Bill Kinney, <cruisingconsulting@...> wrote:
Michael,

As one of the "pre-2K" Super Maramus, our battery box only holds 8 G31 batteries, so our bank has a 480 Amp-hour capacity. Our system allows us to run both generator AND shore power chargers, so with shore power available, we can pump 200 Amps into our batteries, which is very close to the optimum 0.4C charge rate recommended, so no need to think about splitting things up.  

For our battery bank a 120 Amp Charger would be right at 0.25C, which Firefly documents indicate is close to, but above, minimally acceptable.  I assume you have the 12 battery box, so your capacity is 720 Amp-hours, and now the 120 Amp charger is 0.17C, below the minimum recommended by Firefly (0.2 C).

My suggestion would be to contact Firefly Tech support. In the manual they suggest they can recommend an alternative procedure if your charging system is limited to less that 0.2C.  I do not know what that procedure is, but I am curious...

I don't bother turning off the refrigeration units during the draw-down.  They turn themselves off near the end of the run when the voltage drops below about 22.5  Doesn't seem to cause an issue.

Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


Arno Luijten
 

Hi Bill,

The point we had was that we planned to put 10 batteries in the boat but this simply did not fit. The Firefly is just a bit bigger then most G31 batteries, making it impossible to put more then a single row of 9 (incl. starter battery) in the compartment.
I had the system even equipped with 2 Victron battery balancers and each battery tested fine. The graph I got from Firefly showed me the voltages are slighty under "normal" AGM levels:



So to me it seems the batteries are not the best for higher loads when partially discharged. Maybe my set was from a bad batch or whatever but the remark I got from Firefly was:

"...  A couple things you might note, it is fairly normal for the voltage to drop from a 50 amp load at 60% SOC.  It is an inherent characteristic of lead battery chemistry that the voltage is below 12 volts on a 12-volt battery below 50%, and if any load is applied well before reaching 50%. Here is the SOC vs V chart for the FF.  You can see that at 65% SOC the V would be 12.25V with no load applied.
It seems as though lithium might be a better solution for you.
..."

They also told me that a float of 13.3 is too low, but I used 13.3 on my shore charger and 13.5 at the solar charger to minimize the shore power usage. It still did not explain the high voltage drop at higher discharge rates.

So all in all I can't recommend these batteries for an Amel 54 based on my experience.

Kind regards,
Arno Luijten
SV Luna,
A54-121


Bill Kinney
 

Arno,

I agree that the inability to fit a full complement of batteries would be a major problem.  But I am curious why you consider a difference of 0.2 volts a major issue? And it seems you consider 24 Volts an absolute minimum acceptable?  Everything onboard still works perfectly well down to voltages of 23 or so.

The voltage curve you present from Firefly is NOT a zero load curve, but is voltage at the C10 discharge rate, or pulling 50 Amps out of a 480 Amp hour battery bank.  That's a pretty extreme load, and is the one we see only during our deep discharges when we duplicate that curve pretty much exactly. 

We also never discharge below about 60% SOC in normal use.  (About 190 Amps-hrs discharged).  If you need more than that, and on a 54 you likely do, I'd certainly agree that 8 Firefly are not the right choice.

This is our SOC, voltage and current draw graphs from a couple days at anchor. Some sunny, some not :)  Lowest seen voltage is 24.4v on the early morning of the 20th at a SOC of 57% while pulling about 5 Amps. Our generator autostarts at 0630 if the SOC is below 70%, runs to about 93% SOC, and then we let the solar panels take over.


JB Duler
 

Bill, how do you get those charts?
They are great. I used the Victron app but I get limited data.
--
John Bernard "JB" Duler
San Francisco
Meltem # 19, Western Med


Bill Kinney
 

JD,

These graphs are taken directly from the Victron "VRM" website.  With our Cerbo system all of our data (collected every second) is sent to the Victron servers, and is presented on the VRM page in a wide variety of formats.  They store all of the data for six months, and some of it indefinitely.  It has been a real help in understanding our own system, and also to troubleshoot systems belonging to our clients. It can be downloaded and saved forever if you think that is valuable.

I can't be more enthusiastic about the way Victron has set up their systems.  From both a software and hardware standpoint I can't find fault with the route they have taken. Everything we have had from them has just plain WORKED.  They seem to walk that line between options and capabilities and simplicity as well as can be done. Just in the past couple days I have been able to remotely troubleshoot systems on two other boats because Victron is consistent on the way the implement things across their product lines.  I am a fan.

Bill Kinney
SM160, Harmonie
Hollywood, FL, USA


JB Duler
 

Bill, I looked that up, that sounds awesome. I must have been in a cave, or work got in the way. I missed that functionality.
May I ask, does thing connect to wifi or do you need a router on board?
--
John Bernard "JB" Duler
San Francisco
Meltem # 19, Western Med


Arno Luijten
 

Hi Bill,

You did an excellent job in charting the way your batteries are behaving!

I guess I'm just disappointed by the expectations the Sales Blurb set for me about the the way these batteries behave. I consider a 0.1 C load on a battery not exceptional at least not to see voltages dropping to close to 23 Volt. This is a point where all the voltage alarms start sounding on our boat if it lasts longer then 10 secs or so. With an big inverter, a freezer and two fridges getting to these loads is not so hard. The loads are not continuous but long enough to set off the alarms. So in my case the set of batteries I had was not big enough to withstand an excessive voltage drop. When sailing it also means a lot of generator time as the solar panels we have is not be be enough to compensate all usage in the 24h timeframe. Charging was better then with AGM but still the last 20% takes a lot of time. And this is where I got into a catch-22 situation as I wanted the batteries at high SOC because of the voltage drop.
We are now on Lithium and that makes a lot of difference. But that was to be expected. Thanks to the dimensional aspects of the replacement it also allowed us to install 700Ah@24V. But as said before, the cost of this whole exercise is something I really want to forget.

I'm happy these batteries work good for you as I don't believe they are bad batteries but their use-case is different then I expected.

Regards,
Arno Luijten
SV Luna,
A54-121


Alexander Ramseyer
 

Hi to all,
what is your recommendation / best practice to discharge the Firefly batteries to the 10.5V the manufacturer is recommending? I understand, most electrical devices would run into a problem and run very hot on low voltage.
Best, Alex
sv NO STRESS
AMEL54#15


Paul Dowd and Sharon Brown
 

Hi Alex,

 

I am about to take possession of a bank of 8 firefly batteries and assuming you have had yours for a while would be interested in hearing a bit more about your experiences with them.

 

Trust you’re doing well – whereabouts are you these days?

 

Cheers,

Paul

 

Paul Dowd & Sharon Brown

S/Y Ya Fohi, Amel 54 #98
tel: +44 (0)7710 466619

skype: pauldowd
web:
https://my.yb.tl/yafohi

 

From: main@AmelYachtOwners.groups.io <main@AmelYachtOwners.groups.io> On Behalf Of Alexander Ramseyer
Sent: 28 March 2022 11:01
To: main@AmelYachtOwners.groups.io
Subject: Re: [AmelYachtOwners] Firefly Battery Update.

 

Hi to all,
what is your recommendation / best practice to discharge the Firefly batteries to the 10.5V the manufacturer is recommending? I understand, most electrical devices would run into a problem and run very hot on low voltage.
Best, Alex
sv NO STRESS
AMEL54#15


--
Cheers
Paul
Ya Fohi - Amel 54 #98


Bill Kinney
 

Alex,

Just to be 100% clear, the 10.5V discharge is for the individual 12V batteries, that translates to a discharge down to 21V in a 24V system.  I know of nothing that would be damaged running at this voltage.  We take no special precautions during one of these discharge procedures, and have no problems.

Now that we are further south, and past the darkest time of the year, we are in a pretty consistent usage pattern.  We run from 100% in the afternoon of Day 1, down to 78% on the morning of Day 2, up to about 92% on the afternoon of Day 2, down to about 69% on the morning of Day 3.  The generator runs for 90 minutes to charge to 93%, and the solar panels bring it up to full charge by the end of the solar day. If it’s very sunny and we are a bit careful, we go an extra day without generator, if it’s cloudy, we’ll probably need the generator on each day. With our new genset, that takes about 11 liters of fuel a week.

We would love to double our solar panel (from 630W) output, but just can not come up with an installation design we like.  Even with the current fuel prices, it is very hard to justify on a cash flow basis.

Overall, our system works very well supplying our power needs.  The key is that it was designed as an integrated system, with the maximum charging rates and discharge rates of the batteries, total daily power needs, routine state of charge usage, and generator and solar capacity all considered.

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas


Paul Dowd and Sharon Brown
 

Hi Bill,

 

That sounds very encouraging. Do I assume correctly that your bank is 8 batteries?

 

Cheers,

Paul

 

Paul Dowd & Sharon Brown

S/Y Ya Fohi, Amel 54 #98
tel: +44 (0)7710 466619

skype: pauldowd
web:
https://my.yb.tl/yafohi

 

From: main@AmelYachtOwners.groups.io <main@AmelYachtOwners.groups.io> On Behalf Of Bill Kinney
Sent: 28 March 2022 12:44
To: main@AmelYachtOwners.groups.io
Subject: Re: [AmelYachtOwners] Firefly Battery Update.

 

Alex,

Just to be 100% clear, the 10.5V discharge is for the individual 12V batteries, that translates to a discharge down to 21V in a 24V system.  I know of nothing that would be damaged running at this voltage.  We take no special precautions during one of these discharge procedures, and have no problems.

Now that we are further south, and past the darkest time of the year, we are in a pretty consistent usage pattern.  We run from 100% in the afternoon of Day 1, down to 78% on the morning of Day 2, up to about 92% on the afternoon of Day 2, down to about 69% on the morning of Day 3.  The generator runs for 90 minutes to charge to 93%, and the solar panels bring it up to full charge by the end of the solar day. If it’s very sunny and we are a bit careful, we go an extra day without generator, if it’s cloudy, we’ll probably need the generator on each day. With our new genset, that takes about 11 liters of fuel a week.

We would love to double our solar panel (from 630W) output, but just can not come up with an installation design we like.  Even with the current fuel prices, it is very hard to justify on a cash flow basis.

Overall, our system works very well supplying our power needs.  The key is that it was designed as an integrated system, with the maximum charging rates and discharge rates of the batteries, total daily power needs, routine state of charge usage, and generator and solar capacity all considered.

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas


--
Cheers
Paul
Ya Fohi - Amel 54 #98


Bill Kinney
 

Paul,

Our system is 8 batteries, we have an older SM and that is all that fits in our box.

The biggest improvement we have had in our power system was actually rebuilding one of the chest freezers.  We dramatically improved the insulation compared to the OEM installation.  Today--for the first time ever--we have had our solar panels bring the batteries back to 100% for the second day in a row with no help from the generator.  Pretty good for a 630W solar bank.  It is always cheaper to NOT need it than to find another way to make it!

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas


Paul Dowd and Sharon Brown
 

Hi Bill,

 

Sounds very encouraging. I am convinced that our power hungry A54 with 8 FireFlys and 1KW solar will require significantly less generator time than it currently needs.

 

A couple of questions relating to your experiences:

 

What is the lowest % charge state you allow your batteries to fall to?

 

What is the maximum charge current they will draw and what does this fall to when they get to, say, 90%?

 

Cheers,

Paul

 

Paul Dowd & Sharon Brown

S/Y Ya Fohi, Amel 54 #98
tel: +44 (0)7710 466619

skype: pauldowd
web:
https://my.yb.tl/yafohi

 

From: main@AmelYachtOwners.groups.io <main@AmelYachtOwners.groups.io> On Behalf Of Bill Kinney
Sent: 28 March 2022 21:18
To: main@AmelYachtOwners.groups.io
Subject: Re: [AmelYachtOwners] Firefly Battery Update.

 

Paul,

Our system is 8 batteries, we have an older SM and that is all that fits in our box.

The biggest improvement we have had in our power system was actually rebuilding one of the chest freezers.  We dramatically improved the insulation compared to the OEM installation.  Today--for the first time ever--we have had our solar panels bring the batteries back to 100% for the second day in a row with no help from the generator.  Pretty good for a 630W solar bank.  It is always cheaper to NOT need it than to find another way to make it!

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas


--
Cheers
Paul
Ya Fohi - Amel 54 #98


Bill Kinney
 

Paul,

Our control system is set to run the generator if the batteries are less than 70% in the morning.  If the batteries are less than 58% the generator starts no matter the hour of the day.

The charge rate vs. SOC. Curve looks something like this:

170 Amps at 75% This is below absorption voltage, and is the maximum Amps I can generate.

115 Amps at 82%
 78 Amps at 87%
 47 Amps at 92%
 14 Amps at 97%

Firefly documentation considers the batteries fully charged when the charge current drops to 2 Amps for an 8 battery, 24 Volt bank. We routinely see this at the end of a “solar charging day”

The specifications from Firefly suggest that maximum charge rate should not exceed 0.5C, or 240Amps for an 8 battery, 24 Volt bank.  I can not generate this much 24 Volt power, so can’t really tell where it begins to taper off from that.  I am not sure that investing in anything over about 130A of charging capacity for a bank of this size is worth it.  The amount of time it would cut off the normal charging time would be small.

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas