No big battery chargers?

[jr_spyder]

My fridge and freezer are keel cooled models with evaporation plates, not cold plates. When running, each one draws about 4 amps. Of course they cycle on/off 24/7 so I don't really know their daily consumption. But when the genset is running the max load it could be feeding to refrigeration is 8 amps. I only run my watermaker every few days and only when the genset is running. Like yours it's 12 vdc. It draws about 18 amps (to make 16 gal/hr). An interesting idea here would be to only turn on the water maker after the bank goes into absorption phase. The charger should have extra capacity then and there would be no decrease in absorption charging time. That might mean running the water maker more frequently but for less time, which might be a good thing.

[Stu Jackson]

Originally Posted by jr_spyder

My fridge and freezer are keel cooled models with evaporation plates, not cold plates. When running, each one draws about 4 amps. Of course they cycle on/off 24/7 so I don't really know their daily consumption. >>>>>>>>>>>

Then let's help you out here. You say when running they consume about 4 A each. Many folks round it up to 5A, mine runs 4.1 to 4.5 on my Link 2000. That is the typical load for a 12V DC fridge system. For about oh the last two or three decades, studies, lab tests and real time users have confirmed that daily energy use for EACH of these units approximates 60ah per day, calculated like this: 5A x 24 hours per day x 50% duty cycle. Keel cooling, IIRC, may not decrease it much. Better box insulation certainly does.


Now you know.

[a64pilot]

I used to think it was just me, but talking to others, especially if your in the tropics and there is a freezer and not just a fridge, 50% is very, very optimistic. I’d guess mine is closer to 90%, and talking to others it seems many of theirs rarely if ever shut off.

[a64pilot]

Most of us that use a generator to charge, do so with only enough other loads so that the charger can be maxed out and add other loads later like clothes washing, making water etc. when the charger has decreased it’s load enough to be able to do so.
Most of my bigger loads are AC, water maker etc. but the concept is the same, one you have to stay within Generator limits, the other within Charger limits

[jr_spyder]

As for refrigeration I would agree that my refrigerator runs 75-80% of the time and my freezer 95% while now in the tropics. They are much better back in New England cool waters. Certainly more insulation and smaller boxes is the answer, but it ain't broke...

As for running the generator, just for clarity, keep other DC loads low so the maximum amps are going into the bulk charge. I can load up more AC loads, like water heater or aircon units, microwave, with no impact on charger performance. My generator will do 63 amps AC, but the master AC breaker is 50 amps. I've never blown it. If I remember right my charger pulls ~15 amps AC when it starts up. So my big-ish generator is way underutilized. The boat originally had 120vac refrigeration and water maker, hence the now over sized genset. But it should last forever.

[jr_spyder]

Just as a mental exercise I've been doing some math to understand the economics of battery life vs charging with a diesel generator. I'm happy for anyone to tear apart my assumptions and methodology so as to get to a realistic understanding of the economics.

a. My Westerbeke 8kw generator burns 0.9 gph per spec
b. Assume diesel at $4/gal
c. My 750AH house bank cost $2,100 in the US
d. Spec lifetime of my batteries at 50% discharge is 1300 cycles
e. Assume 2 hours charging time to go from 50-80% SOC. This is $7.20 in fuel
f. Assume 4 more hours charging time for go from 80-100 SOC. This is $14.40 in fuel
g. Assume battery lifetime is reduced by 30% when short-cycling, or down to 910 cycles (lost 390 cycles). (Note the tech guy at my battery company guessed life would be reduced by 20-25% when short cycling - this is the only info I have to go by - might be better data out there)

1. To maximize battery life by always doing the extra 4 hours charging to 100% means 1,300 x $14.40 = $18,720 in fuel (not to mention 5,200 additional hours on my genset, and 52 more oil changes!). Realistically charging to 100% means 40% fewer cycles (diff between consuming 30% of the capacity or 50% per cycle), so the 1300 cycles stretch out over a longer period of time (if other things don't kill the bank sooner). So let's say $18,720 - 40% = $11,232 is a closer realistic cost differential to get equal capacity and maximum life. Compare this to replacement batteries at $2,100 and it looks obvious that short cycling and shorter life is economically better that full recharging every cycle with a generator.

2. Another layer of math should be done here to look at charging to 100% every few cycles. I'll make two somewhat random (and potentially very wrong) assumptions: Do a full charge every 5 cycles, and assume battery life is only reduced by 15%. So we'll get 1,105 cycles, and charge to 100% 221 times which equals an additional $3,182 in fuel. Better, but still not attractive economics.

3. Change these assumptions in any conservative/generous way possible and it will still be hard to justify the cost of max life over short cycling.

4. This really says add solar/wind and get it right at any reasonable price.

5. It also is a very good argument for LFP batteries at much higher initial cost but far less charging time, more available capacity each cycle, and more cycles in their lifetime.

6. This same analysis could be done for different levels of discharge/recharge, with different outcomes.

7. Don't shoot me. I'm completely ignoring real life that sometimes you motor, and sometimes you plug in. Those charging cycles improve the economics. Your genset fuel consumption might be much lower than mine (I hope so!) Batteries and fuel cost are very different in different parts of the world. This is a framework, not a PhD analysis. Truth is most of these numbers seem too big to be true. What did I miss?

Very happy to debate and learn.

JR

[Exile]

I don't think you're missing anything. I haven't crunched the numbers for myself, but it seems the general consensus I've been reading for years is that using a generator or engine solely to get batts. from 80/85 to 100% is not economical. The variables can change when you're also running your engine for propulsion obviously, or using the genset to make water, run 110v appliances, etc. The economies may also change if you have an expensive AGM bank which is less tolerant of not getting fully recharged.

Fwiw, my WB 8kw burns closer to 0.5gph.

[a64pilot]

Well to begin with it’s my opinion that 20% reduction in life for an AGM bank is extremely optimistic, I’d say if your going 50 to 85% it’s more like 50%, especially if you can’t or don’t equalize, equalizing if your batteries are capable, would help a lot.
My opinion is you need to do one of three things.
1. Get Solar and use it to finish charging the bank to 100%, still likely need a morning generator run, but likely much less than you do now.
2. Get a Honda, fill it up with .9 gals of gas (full tank I believe) and run it until the batteries are full, likely take 6 hours, which will be most of that .9 gals of gas, but oil changes are easy and it holds almost no oil and the generator costs $1,000 and will it appears will last several thousand hours, how many I don’t know, but it’s cheap to buy and run is the point.
3. Your next bank should not be under any circumstances be an expensive AGM bank, golf cart batteries are I believe about $1 per AH, so $750, and will likely last almost twice as long as your AGM bank being charged from 50% to 85%. The downside for it being 1/4 the cost when amortized out is you have to add water every now and then, AGM’s you don’t.

AGM’s have their use of course, everything does, just unfortunately what your doing with them makes them the most expensive battery to use.

Your charging the “old” way, back when Solar was major $$$ and so was wind so most charged with their alternator and just bought a new bank every couple of years, but banks then were tiny cause average boat only had a few lights to run, refrigeration was for the big buck yachts, so tiny banks weren’t expensive to replace.

Now don’t think I’m beating on your for buying AGM batteries, I have AGM batteries, so if you screwed up, so did I.

On edit, a Honda 2000 will run a charger at 100 amps, and of course as they begin to charge up it will slow down in RPM and burn less fuel, so it’s that low load time that it makes more sense money wise to run a suitcase generator as opposed to your big boy, save it for when you need a man to pull a load the Honda can’t.

A little Honda changes the economics quite a bit, figure about 8 hours average per gl of gas. I believe the numbers are actually 6 hours under heavy load and 9 hour under light load, but look it up. I’m not sure, but of course you have to amortize the replacement cost of a generator to get the true cost of running one, and once you add that number in, you can see how expensive it really is to run one.
For my little 3.5 kw generator I figure $1 a hour for replacement costs, a Honda is more like .25c an hour, maybe a little more.
I only have a guess on how long one will last and I get that from Alaska forums it seems the little Honda’s are and have been used there for a long time

[Exile]

Originally Posted by a64pilot

Now don’t think I’m beating on your for buying AGM batteries, I have AGM batteries, so if you screwed up, so did I.

On edit, a Honda 2000 will run a charger at 100 amps, and of course as they begin to charge up it will slow down in RPM and burn less fuel, so it’s that low load time that it makes more sense money wise to run a suitcase generator as opposed to your big boy, save it for when you need a man to pull a load the Honda can’t.

I go with AGMs mainly because all my batteries (3 8Ds & 1 G24) are located under my bunk. Kinda concerned about that amount of FLAs gassing off, but maybe for naught. But I also buy Lifeline's since they can be conditioned.

As far as suitcase generators go, would it be safe to assume that a 1K unit would suffice to run a 50A charger once the banks have finished their bulk stage? I would think so. The downsides, I suppose, are the extra gas plus stowage.

[a64pilot]

Mine are Lifeline too, but that because my battery box is too short to fit GC2’s.
I think my next bank will be Gel.
Anyway my Honda 2000 will run my Magnum charger at 80% which gives a 100 amp charge, 50 amps is easy and would have it purring.
A 1000W generator ought to run a 50 amp. If a 2000 can do 100.
However why buy a 1000? The 2000/2200 is pretty much the accepted standard, and of you ever wanted to sell it, it’s my understanding that they sell very quickly.
Of course I’m not sure the 2000 is even made anymore and unless you can get a real deal on one, I’d buy the 2200, which may run my Magnum at 100% or 125 amps, it might, maybe as it’s a 10% more powerful generator than a 2000.

I’d buy the 2200 even to run a 50 amp charger, because the 1000W one would do it, but it’s working hard and making lots of noise, where a 2200 is loafing at low RPM and is sipping fuel and is quiet.

What would be interesting to know is what is the fuel burn difference between a 1000W generator making 1000W or a 2200W generator making 1000W.
I bet it’s not much different.

[Exile]

I already own an older but lightly used Yamaha 1000w which still runs well. Not sure I want to carry it onboard but I do understand their utility. Thanks for the explanations & info. Most helpful.

[jr_spyder]

Originally Posted by Exile

The economies may also change if you have an expensive AGM bank which is less tolerant of not getting fully recharged.

I do have an expensive AGM bank and my math was based on its specs including cost.

Originally Posted by Exile

Fwiw, my WB 8kw burns closer to 0.5gph.

That's good to hear. I believe mine runs less than the .9 gph in the spec but my testing has been imperfect. I'd really like to know the truth and will do a much more scientific test at some time. Should be interesting. This factor - fuel usage - and the price of fuel have the biggest impacts on the equations.
a64's clever solution with a suitcase generator seems to optimize these two factors.

[jr_spyder]

Originally Posted by a64pilot

Well to begin with it’s my opinion that 20% reduction in life for an AGM bank is extremely optimistic, I’d say if your going 50 to 85% it’s more like 50%

Well I used 30% in my calcs, but I can believe it could be 50% reduction in life. Even then the economics stay better to murder the batteries through short cycling than recharging to 100% in my situation. Very sad but true. All the rest of your advice is valuable and has me thinking about changes I'll make when this bank dies (or for the next boat...). But it's what I've got for now and I just want to optimize for what I've got.

I've learned a ton from this thread and have enjoyed doing so. Thanks everyone.

[Stu Jackson]

It has been interesting, and you probably understand that you're reinventing the wheel.

4. This really says add solar/wind and get it right at any reasonable price.

5. It also is a very good argument for LFP batteries at much higher initial cost but far less charging time, more available capacity each cycle, and more cycles in their lifetime.

4. Of course, folks have been saying this for decades now.


5. Another fine choice is wet cells, lots less expensive and more tolerant of PSOC. Before solar, folks ran their banks between 50 and 85% because they understood battery acceptance and how long it takes to get that last 15% in. Now folks go buy much more expensive batteries that, up front, warn about PSOC and simply choose not to heed advice and have inadequate charging systems to SUPPORT the very technology that they chose to purchase.


How come?



Good luck.

[Kenomac]

Wow, lots of wrong info on this thread. Little Harbor 46, Nice Boat!

BIGGER is BETTER when it comes to charging. We increased our 50am charger to 125amps by adding a second Mastervolt unit, the batteries now charge up much faster.