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deckofficer · 03-12-2013, 15:47

Quote:

Originally Posted by Opie91

It would be neat if someone took a new 100 ah lead battery and put it to the same test. I wonder how many cycles it would make. Ill pitch in $20.

Couldn't do this as a apples to apples comparison. A 100 a-hr group 27 or 31 LA battery at just a 15 amp load will only have a capacity of 72 a-hr. At the 94 amps that I'm pulling the capacity would further de-rate to about 30 a-hr.

Cycle life by itself doesn't have useful information without knowing how much work the battery is doing.

If the LiFePO4 cells cycle 2000 times, producing full a-hr rating at 1 C, then over these cycles stored and gave up 2000 X 100 a-hr.

On a LA battery, if it could do 300 cycles it would take in via charging 300 X 100 a-hr, yet deliver only 300 X 30 a-hr (Peukert @ 1 C).

Since charging sources are minimalistic on our boats, you would want to maximize usable stored energy vs input energy. If loads are higher than the 0.05 C that LA is rated at, then for every a-hr you put in, you only get a percentage out. That alone should convince cruisers to invest in a LiFePO4 bank, along with weight reduction, cycle life, no gassing, no voltage sag under load, and all the other perks.

Aikiguy · 03-12-2013, 15:54

Hey Bob where are you getting your cells, looks like they are working pretty well for you.

Guy
:-)

deckofficer · 03-12-2013, 16:12

Quote:

Originally Posted by Aikiguy

Hey Bob where are you getting your cells, looks like they are working pretty well for you.

Guy
:-)

I got mine from Balqon. They have a minor blemish to their reputation with sometimes slow delivery of cells and having some old stock. Mine were 3 years old before I got them and another customer that is active on this thread had a long wait for 400 a-hr cells so Balqon stepped up and sent him 700 a-hr cells for the price he paid for the 400's that weren't in stock. The real life "slow boat from China" scenario. They do have the best prices, and their clearance stock is really good prices like $560 for 700 a-hr cells.

Balqon Electric Vehicle Manufacturer

Maine Sail · 03-12-2013, 16:44

Quote:

Originally Posted by Opie91

It would be neat if someone took a new 100 ah lead battery and put it to the same test. I wonder how many cycles it would make. Ill pitch in $20.

Shooting from the hip I would say the vast majority of my new customers, who coastal cruise, get less than 125 cycles to approx 50% SOC (many are well below 100 cycles when their batts pack it in.....

In querying them on use, charging etc. I find their batts are cycled between 15 and 30 times per year, on average, and they last between 3-5 years, on average. A one week cruise and 12-15 overnights is a good year for many. This amounts to about 20-30 cycles per year for a fair majority of boats.

With better care LA's can last a lot longer but most people simply don't treat their batts well.

The old FLA batts I took of our boat are still going strong at year 8 but they have only about 350-375 cycles on them. However this was to an average DOD of just 70% SOC NOT to 50% SOC... I shallow cycled them, took advantage of the Peukert effect, and they lasted and are still going. That however is a LOT of "dead lead" to be slugging around for 30% usable capacity. I now have 80% usable capacity, the voltage never sags under house loads, and the bank weighs less than HALF what the old one did.....

diugo · 03-12-2013, 17:38

Bob, the resting voltage for LFPs is pretty meaningless because of the distinctive plateau feature of the capacity curves---which are all representative of a specific charge/discharge current. At rest (ie zero current) the curve essentially devolves to just the plateau.

This is why it's so hard to glean an accurate SoC from cell voltage.

Speaking of accuracy, how are you measuring the high discharge current drawn by the space heater?

deckofficer · 03-12-2013, 17:59

Quote:

Originally Posted by diugo

Speaking of accuracy, how are you measuring the high discharge current drawn by the space heater?

Unlike Maine Sail, I don't have an Amprobe. Just math, heater on lower setting is 1100 watts.

diugo · 03-12-2013, 18:37

Several problems with using just math: 1. No way of knowing if the heater is really producing the advertised 1100W. 2. Inverter efficiency is not being taken into account. 3. Assuming the inverter maintains constant AC voltage (as it should) then battery current cannot be constant, ie it must increase as battery voltage falls from 13.4V to 11.7V.

You really do need some way of truly measuring battery current. No overpriced clamp probe is necessary---you can get a current sensor module like this one 50A 100A 150A 200A Bi Uni AC DC Current Sensor Module Arduino Compatible | eBay on eBay for under $20 or one of these cool babies "Watt's Up" RC Watt Meter Power Analyzer WU100 Ver 2 | eBay for under $50 delivered.

deckofficer · 03-12-2013, 20:08

Doug,

I'm not going to run all these cycles on assumed amp draw. Since the China made clamp on amp AC/DC meters are only $50 I ordered one from Sears.

diugo · 03-12-2013, 20:17

Great! With accurate current (and time) measurement you'll be able to calculate your cells' Peukert as well.

careka · 04-12-2013, 12:41

Here is more info.
My E-Life Now !: LiFePO4 Battery Charging Method - Don't Ruin your Expensive Cells !

boatpoker · 04-12-2013, 13:59

I know very little about Li batteries and have never even seen any on a boat until a couple of weeks ago. Then two more last week. I am reading furiously trying to get caught up and am fortunate to have access to a brilliant electrical engineer who is up on these things (no, he does not work for Boeing

This link is to photos of the first installation I saw. These batteries have absolutely no markings on them and no monitor other than a cheap LED voltage indicator.

I'd appreciate it if anyone can identify these batteries as I'd like to learn more about them.

Thanks

Maine Sail · 04-12-2013, 14:15

Quote:

Originally Posted by careka

Here is more info.
My E-Life Now !: LiFePO4 Battery Charging Method - Don't Ruin your Expensive Cells !

Bottom balance is good for EV & scooter or electric bike guys who regularly use all the capacity. On boats we are running light loads and only discharging to 80% DOD. If you have a cell hit the LV threshold at 80% DOD you have MUCH bigger issues to resolve...

The problem we have on boats is MULTIPLE charge sources, EV guys usually have one source. Preventing over charge is more critical on a boat due to the nature of use.

A single top balance may be all you ever need. I am over 200 cycles most to 80% DOD and my cells are still in balance out to .002v - .005V. All I did was wire them in parallel and let them sit for a day. I then charged the parallel wired pack to 3.8V in parallel and it was done.... In use all my charge sources are set to 13.8V and charging is terminated at 5A +/-.... My bank is NEVER allowed to get to shunting voltage levels and my BMS is only there as an insurance policy.

deckofficer · 04-12-2013, 14:15

careka, good link, thanks. I agree with Jack Rickard about not using a BMS and that the use of a BMS has probably killed more cells than they have saved. I would have liked to bottom balance the way he suggested, bringing each cell to 2.8 volts on the money then hooking all the cells into the series string that will be the EV voltage and charging to full. For me this would have been so much faster and easier than hooking all the cells in parallel and charging with a 30 amp PS. He is completely against shunt balancing systems found in BMS and I agree.

Today my cells have the easy task of powering a 32 inch LCD TV instead of the space heater. Been running the TV for 4 hours 15 minutes so far, voltage under this load and time frame is 13.02 volts.

A side note, this inverter is a Aims bargain basement 2000 watt modified sine wave at a cost of $190. Consumes 12 watts just to be on without load. I was concerned that my HDTV wouldn't like anything other than a clean full sine wave power but other than a very low buzz that can't even be heard unless you turn down the audio, no problems. Does anyone know what items will not tolerate the cheap mod sine wave inverters? Probably a laser printer.

deckofficer · 04-12-2013, 14:19

Quote:

Originally Posted by boatpoker

I know very little about Li batteries and have never even seen any on a boat until a couple of weeks ago. Then two more last week. I am reading furiously trying to get caught up and am fortunate to have access to a brilliant electrical engineer who is up on these things (no, he does not work for Boeing

This link is to photos of the first installation I saw. These batteries have absolutely no markings on them and no monitor other than a cheap LED voltage indicator.

I'd appreciate it if anyone can identify these batteries as I'd like to learn more about them.

Thanks

Your picture link showed what looked like a Optima AGM battery which is a lead acid battery, not LiFePO4.