FireFly Battery Notes II

[OceanPlanet]

Originally Posted by rgleason

Is charging at 0.5C on a regular basis acceptable?

Sure! Btw, it's a good idea to have voltage temperature compensation from ambient temps near the batteries. So that in warmer ambient temps the voltage is cut back some. Firefly says it's ok for the batteries to warm up themselves some while charging, which is apparently why using ambient near them for temp. comp. is good.

The recommended temp. comp. is 24mv/C, or 13mv/F, from the base temp of 25C/77F (reduce voltage if >25C, raise voltage if <25C)

[rgleason]

After learning about LFP and considering the resultant systems, and this small boat, I think that a Firefly installation would be simpler and more robust. While the Firefly may be a bit heavier and bigger than LFP, the batteries can remain in the port cockpit locker where they are now and they will charge faster (0.5C for Firefly vs 0.35C max for LFP). I assume that as they get above 80% the resistance will go up and they won't charge as fast, but it is not necessary to be as concerned about sulfation. I now realize, as a result, that the effective battery capacity will not be nearly as much as LFP (.7x200ah=140a for LFP vs .4 x 200ah= 40ah). That is a significant difference, so I would probably need a 3rd battery and there is no room for that. Humm... Any thoughts?

Below was written earlier...

With ARS-5 or Al Thomson's VSR Alternator Regulator Gen3 (precursor to Wakespeed WS500) I will have alternator temp at the alternator and battery temp at the battery.

Thank you very much, I will use those settings. Since it is on a mooring and I don't plan to run the alternator for hours, every week or couple of weeks, what size (watts) is appropriate to recharge 200ah of (2) 12vdc Firefly Odysey back to full charge from say 80% or 90% over (5-7 days) in RI in the summer? 100watts or 200watts?

It looks to me like cruising with alternator charging in the morning while going in and out of harbors (1.5-2hours per day) at 100a (which is .5C x 200ah) is going to be completely possible with a daily total load of 80-90ah. At sea with 135-140ah daily load some additional solar over the helm as shade, will help a lot.

[rgleason]

Correction
.7x200ah=140a for LFP vs .4 x 200ah= 80ah for Firefly

It looks like a 3rd battery would not be needed!

[crayiii]

Originally Posted by rgleason

Correction
.7x200ah=140a for LFP vs .4 x 200ah= 80ah for Firefly

It looks like a 3rd battery would not be needed!

Keep voltage drop in mind. My understanding is LFP doesn’t have the same voltage drop issues so while you may be able to run the firefly batteries down to a low SOC without sulfation issues, you may run into voltage that is lower than some equipment requires.

[MerMike]

40% depth of discharge is pretty conservative. From the Firefly datasheet:
50% DOD
~3600 cycles

80% DOD ~1000 cycles

A third battery may not be needed depending on your use.

Originally Posted by rgleason

Correction
.7x200ah=140a for LFP vs .4 x 200ah= 80ah for Firefly

It looks like a 3rd battery would not be needed!

[sailorboy1]

this isn't really about FireFly batteries

But when is doubt/question it is better to have more battery than less. IF the no sulfacition is true the lower discharge and resulting longer life may be less expensive or the same of the lifetime of the batteries. But then again the lifetime is projected to be so long than it will probably never be seen by the original buyer.

[rgleason]

Originally Posted by MerMike

40% depth of discharge is pretty conservative. From the Firefly datasheet:
50% DOD ~3600 cycles
80% DOD ~1000 cycles
A third battery may not be needed depending on your use.

Thanks MerMike, for pointing that out, I had not studied that aspect in detail. Also earlier I was not clear about my assumptions.

I assume that normally 50% DOD is from 100%- 50%SoC and
80%DOD is from 100%-20%Soc

I don't want to deal with or face the daily uphill engine-alternator charging of the Firefly Odyssey batteries from 80% - 100% SoC which is far less efficient and requires many hours of engine time. I would like to have enough solar watts on board to have the batteries reach 100% SoC while on the mooring, over a 5-6 day period. We normally cruise for 2-2.5 weeks a number of times during the season (fall-spring). I don't yet know what size PV will be needed.

Therefore I have assumed that daily use and engine alternator charging would occur between 80%-40%SoC (hoping to get 3000 cycles) which is .4C .

Hope that seems reasonable.


CrayIII thanks.

Does anyone know the expected voltage of these batteries at 40% SoC?

[MerMike]

Originally Posted by rgleason

Does anyone know the expected voltage of these batteries at 40% SoC?

It would be hard to measure in a working system, since it's a resting voltage. I've seen anywhere from 2 to 24 hours at rest before measuring.

I haven't seen a reference specific to the Firefly for either voltage=SOC or time at rest, but would like to know if someone finds it.

[sailorboy1]

So far I have found my FF batteries voltage to be the same as my old Trojan T105s under operation as the same SOC. Couldn't tell you want 40% was as I never let them get that low.

[rgleason]

Thanks, I looked up the Trojan User Guide

50% SoC Specific Gravity 1.172 Voltage 12.10

40% SoC Specific Gravity 1.148 Voltage 11.96


I think Nav equipment will work.

[crayiii]

Originally Posted by rgleason

Thanks, I looked up the Trojan User Guide

50% SoC Specific Gravity 1.172 Voltage 12.10

40% SoC Specific Gravity 1.148 Voltage 11.96


I think Nav equipment will work.

I have not been able to get anywhere near usable voltage out of AGM (haven't had the FF long enough to know) batteries to get down to 50% when a normal house load is on them.

If you're interested, here's a video that has pretty good test data about this.

https://youtu.be/iy3hga_P5YY

[rgleason]

Originally Posted by crayiii

I have not been able to get anywhere near usable voltage out of AGM (haven't had the FF long enough to know) batteries to get down to 50% when a normal house load is on them.

If you're interested, here's a video that has pretty good test data about this.

https://youtu.be/iy3hga_P5YY

Crayiii Sorry but I don't understand what you mean, "I have not been able to get anywhere near usable voltage out of AGM (haven't had the FF long enough to know) batteries to get down to 50% when a normal house load is on them."


I have seen this youtube from beginning to end, before. It is good. I didn't see any data about voltage vs soc specifically.

[crayiii]

Originally Posted by rgleason

Crayiii Sorry but I don't understand what you mean, "I have not been able to get anywhere near usable voltage out of AGM (haven't had the FF long enough to know) batteries to get down to 50% when a normal house load is on them."


I have seen this youtube from beginning to end, before. It is good. I didn't see any data about voltage vs soc specifically.

I meant to say AH. Voltage sag prevents truly getting the rated AH from the battery in a usable manner. When a battery brand says you can take their battery to 50% SOC that doesn't mean you can do that at 12v (in my experience). Maybe if you're only pulling 1 or 2 amps.

That's probably well known and just the common practice of rating batteries. It just doesn't line up with the way I think (I'm weird though).

[rgleason]

Yes, agreed, you bring up a good point about discharge rate. I think it would work for my instruments and nav instruments < .05C , but not 10a of autopilot in addition. Voltage.

[dfelsent]

Originally Posted by crayiii

I meant to say AH. Voltage sag prevents truly getting the rated AH from the battery in a usable manner. When a battery brand says you can take their battery to 50% SOC that doesn't mean you can do that at 12v (in my experience). Maybe if you're only pulling 1 or 2 amps.



That's probably well known and just the common practice of rating batteries. It just doesn't line up with the way I think (I'm weird though).

To me, that sounds like bad connections, or more likely dying (low capacity) or not fully charged batteries, or sulfated cells.
Or maybe an undersized bank for the load.

Or measurements done not directly on the battery posts combined with high resistance connections.

Also , remember 12v is a nominal number.
Not a voltage you can expect to actually see in real life. Often more, sometimes less.

If my 450AH bank at 50% nominal discharge and a ten amp load was below 12v I’d look for problems.