In-Depth RV Lithium Install & Wiring Film - Mike Mas

[markopolo]

Originally Posted by RossWilliams

..........if your batteries only have a peukert rate of 1.1. and your AC and inverter take 1700 watts combined...................

The 1700 watts is the primary problem there. A more efficient A/C running off a good inverter would be around 1200 watts. The 13,500 BTU A/C in a Class A I had would take 90 to 100 amps when running off the inverter whenever I tested it. I had a not very efficient 15,000 BTU A/C in a Travel Trailer that ran at 1600 watts - I soon forgot about running that off batteries.

Originally Posted by RossWilliams

..........So, for instance, an 800 ah agm with a peukert constant of 1.15 will give you 101.84 minutes at 8 amps to 80% depth of charge while the lithium 800ah will give you 80 minutes at 8 amps. So, absent the heavy draw of an AC, the AGM's actually provide more capacity at the same AH rating assuming both are drawn down to 80%.................

For lithium you'd probably expect:
800Ah capacity / 8A draw = 100 hours
800Ah x 80% = 640Ah /8A draw = 80 hours
Some lithium batteries are rated more conservatively than other though. The ones that promise X Ah at 100% DOD sometimes actually have an original capacity greater than X Ah.

For 800Ah AGM with Peukert 1.15, if I'd do the calculation on a per battery basis I get 90 hours runtime at 100% DOD and 72 hours runtime at 80% DOD.

I used this calculator: http://www.smartgauge.co.uk/calcs/peukert3.xls

No doubt you meant hours and not minutes but how did you come up with 101.84? What numbers and what calculator did you use?

[RossWilliams]

Originally Posted by markopolo

No doubt you meant hours and not minutes but how did you come up with 101.84? What numbers and what calculator did you use?

The spreadsheet formula is this:
N6*POWER(N3/(N6*N4);N2)

translated:
n6*(n3/(n6*n4))^N2

where
n6 = 20AH
n3 = 800 ah
n4= 8 amps
for the agm n2= 1.15
for the lithium n2= 1

edit: n6is actually 20 hours , the period of time used to determine n3 which is the battery capacity rating. N4 is the number of amps actually drawn and n2 is the peukert effect.

But frankly its irrelevant. You are right - if the lithium ah is based on its usable capacity being 800 ah and you compare it to an agm battery rated at 800 ah then you are comparing apples and oranges.

That does not change the essential point. The higher the draw, the greater the advantage for lithium batteries. The lower the draw, the more advantage there is for agm batteries. The scope of those differences changes depending on the capacities of the batteries and the size of the draws.

[markopolo]

Thanks for explaining it. I see that I used 8 x the current in my previous post.

For 800Ah AGM with Peukert 1.15, if I'd do the calculation on a 1A per battery basis I get the same 101 hours runtime at 80% DOD that you did.

[markopolo]

So for small loads you'd have to buy 25% more lithium compared to AGM to get the same runtime?

Is that right? Seems like a huge difference.

[booster]

Originally Posted by markopolo

So for small loads you'd have to buy 25% more lithium compared to AGM to get the same runtime?

Is that right? Seems like a huge difference.

And with lithium, you get what you buy, another AH usable gives and AH of use. With AGM as you increase capacity, you are also changing the "hour" capacity rating of the bank assuming you use at the same rate as before. So as you increase capacity, you also increase the capacity of the existing batteries because they are running at a higher hour capacity rating.

[RossWilliams]

It is a large difference, but remember this is at 8 amps and 800 ah batteries rated using 40 amps. That is a large difference in current and the peukert effect is exponential. If you compared 400AH batteries the difference would be 40 hours lithium versus 45 for the AGM. That is the same as when the batteries are at 800AH and the current is doubled to 16 amps.

I think it indicates that if you want to use low draws over days of boondocking, the AGM batteries may be a better fit. Or, more accurately, you may want to compare the batteries using AH ratings for periods longer than the standard 20 hour rating.

You also need to be sure that the lithium manufacturers are using the same numbers. Many (most?) lithium batteries have built in BMS that prevent the battery from being run down below 20% SOC. Whether they count that extra 20% when rating the battery may vary.

[booster]

We have talked about this many times in the past, but when using Peukert to calculate your usable capacity you need to understand that the lower number of AH you get at high discharge rates does not "lose" the energy compared to a low discharge rate. That energy is still in the battery, minus a very small amount that went to extra heat during discharge and will be there to use at a lower discharge rate. Here is the Lifeline capacity charge by hour rating discharge rate vs resulting capacity.


Of interest to note is the ending voltage for all the curves is 10.5v which is the arbitrary cutoff voltage for a discharged battery. What happens is that you get to 10.5v at a lower amount of AH and total watt hours earlier because of voltage drop, not lost energy. If you let the battery recover for a while and then use a lower discharge rate, it will not hit the 10.5v cutoff until the AH amount for that smaller discharge rate.


In the chart above if you use the 4 hr rate which about what you would get from a 440AH bank of batteries running the AC, you would get about 81% of the 20 hour rating before 10.5v cutoff. If you then switched to the 120 hour rate, you would get another 33% of capacity until you hit the 10.5v again. That is about a 40% increase in what you think you had just using Peukert for checking actual energy in the bank.


This could be very important to note for the way some people use their vans. Say you drive on a hot day and then park in a no shore power site with a hot van, hot engine and the sun still shining. You could run the AC on batteries to shutoff, 4 hours in our example, and then shut off the AC and use at the 120 hour rate and you would be able run for another 40% of capacity approximately because the energy is still there.


The AC use is an extreme example, but microwave use or other high amp draw things will only use the AH they use, not more based on the high amps. Once you go back to normal loads, you have not lessened what you have left compared to the same AH used at low draw.



I know there are those that don't believe this, but I would suggest they actually test it to find out, as I have done that test several different times and it is always exactly how it works. A quick and dirty test would to run the AC until you it cutoff at 10.5v and shut everything off until the battery voltage stabilizes. It will be above the 10.5v for sure. The listed state of charge from a chart for your battery style will indicate what the state of charge actually in in the battery based on the 20 hour rate and that power is usable at the lower amp draws than the AC. Peukert would indicate that battery to be totally discharged as it hit 10.5v cutoff, but it isn't.

[avanti]

Originally Posted by booster

I know there are those that don't believe this

No one who learned about the conservation of energy in high school physics.
How could it be otherwise?

[JonK]

Oh, I'm a believer and I'm still trying to convince my battery to be one, or at least produce the evidence that it does.

I have a 10.1Kwh battery with 90% of that usable or about 9.1 usable. When I ran a test at 1.8 amp load, two different ways the calculated capacity is around 6Kwh. Calculating the capacity in watts requires tracking the voltage over a 60 hour period in this case - let's just say I like my sleep and did some extrapolation to get the results above.

I then ran a test running the A/C with the doors open and the battery reached its shutdown in 4+ hours having consumed a calculated 7KWH. Readings were taken every half hour in this case. I just put the charger on it after this test - silly me I really would have benefited from evaluating the recovery.

I need to run more tests since these results make to sense in relation to each other: a smaller load producing less capacity to shut down point than a high load. I suspect a methodology error though I don't know what it is yet.

I have no disagreement with anything posted in the previous postings; I really admire the quality of this discussion. For me, and no this isn't really a "but", boondocking time is only half the equation, charging time is frequently important as well. I'm wondering if at time an AGM would perform better on discharge and a lithium better on recharge, or even the opposite at times. If I'm understanding this all correctly (yeah right, duh) the selection of the battery requires an in-depth look at projected usage pattern and then calculations that I forgot how to do decades ago. Whatever our choice, it is a bet on a future that probably won't match the actuality. I love this stuff, but not in a directly usable linear rationale way. Rather it's feeding me a broad perspective and supporting better intuition as to my choices. Geez, I hope this makes sense, it sort of does to me.

[booster]

Originally Posted by JonK

Oh, I'm a believer and I'm still trying to convince my battery to be one, or at least produce the evidence that it does.

I have a 10.1Kwh battery with 90% of that usable or about 9.1 usable. When I ran a test at 1.8 amp load, two different ways the calculated capacity is around 6Kwh. Calculating the capacity in watts requires tracking the voltage over a 60 hour period in this case - let's just say I like my sleep and did some extrapolation to get the results above.

I then ran a test running the A/C with the doors open and the battery reached its shutdown in 4+ hours having consumed a calculated 7KWH. Readings were taken every half hour in this case. I just put the charger on it after this test - silly me I really would have benefited from evaluating the recovery.

I need to run more tests since these results make to sense in relation to each other: a smaller load producing less capacity to shut down point than a high load. I suspect a methodology error though I don't know what it is yet.

I have no disagreement with anything posted in the previous postings; I really admire the quality of this discussion. For me, and no this isn't really a "but", boondocking time is only half the equation, charging time is frequently important as well. I'm wondering if at time an AGM would perform better on discharge and a lithium better on recharge, or even the opposite at times. If I'm understanding this all correctly (yeah right, duh) the selection of the battery requires an in-depth look at projected usage pattern and then calculations that I forgot how to do decades ago. Whatever our choice, it is a bet on a future that probably won't match the actuality. I love this stuff, but not in a directly usable linear rationale way. Rather it's feeding me a broad perspective and supporting better intuition as to my choices. Geez, I hope this makes sense, it sort of does to me.

At 10.1KWH you must have lithium batteries, which would have a Peukert of effectively 1.0 so there is not a real change in AH recovered at various load rates. This would be for AGM which was mentioned a bit earlier in a post about lowering the draw also increases the usable AH in AGM batteries.


I would not expect you to see any measurable difference in your lithium bank.


You mention the AGM possibly doing better on discharge and the lithium on charge, and that is very possible.


Several on here have done hybrid systems with both types in place at the same time. The smart way is to charge the lithium quickly and then use it to charge the AGM and it's long absorption time through a B to B charger. Perfect for periodic generator or big alternator charging runs so you don't have to run long hours to take care of the AGM batteries.

[JonK]

Booster: thanks for educating me. I thought all batteries had that characteristic. So my battery knew what it was doing and I was clueless as usual.

Do you know if all lithium batteries perform at 1.0 or does it depend on the particular chemistry. My lithium are LNMK (I believe or something to close to that)

Thanks again,
Jon

[booster]

Originally Posted by JonK

Booster: thanks for educating me. I thought all batteries had that characteristic. So my battery knew what it was doing and I was clueless as usual.

Do you know if all lithium batteries perform at 1.0 or does it depend on the particular chemistry. My lithium are LNMK (I believe or something to close to that)

Thanks again,
Jon

Others will probably know for sure, but I think essentially all the common lithium chemistries are very close 1.0.

[markopolo]

High discharge rates with LiFePo4 do result in less output to the voltage cut-off point but it's probably hardly noticeable on the large banks in RV's.

It's more easily observed with smaller capacity cells. Here's a test on a 6.5Ah LiFePo4 cell:

https://lygte-info.dk/review/batteri...ray)%20UK.html

[IdleUp]

Hey guys - We had another great “Off The Grid” trip in our Lithium RV over the Holidays on a ride to Cincinnati, Ohio to to pick up our new BMW i3. The trip was five days and we never plugged one time or stopped at a campground. The battery system operated flawlessly to provide plenty of heat at night as well as run the entertainment devices. The beauty of lithium RV conversions such as mine is they offer the ability to spend a night where you want to stay, rather than in a campground miles from your destination. For this trip we ended up staying two nights right on BMW dealers lot, surrounded by millions of dollars of new BMW’s as they prepped our new I3.




While on the subject of lithium, new technology in lithium chemistry is transforming electric cars and RV's. Using the same battery space my older I3, the new BMW i3 has almost tripled its electric mileage.

Our older 2014 I3 had a range of around 60 miles on battery and 58 miles on gas for an average good weather total of 120 miles. Thanks to this new lithium technology, the original 18 kWh battery has been replaced with a 42.2 kWh. / 120ah pack. The i3 can now travel 180 miles on electric and 85 miles gas for a total of 265 miles.

Should you run low on battery, the I3 RX version includes a gas powered range extender using a de-tuned BMW 650 motorcycle gas engine. So if you're going on a long trip you can either fuel up with gas or stop at a number of Walmart's new network of super chargers which can charge the i3 battery to 80% in 20-30 min.



Since we’ve been back the temperatures have been getting down to 25-35 degrees at night. Thanks to special venting I incorporated to circulate air from the trunk to the coaches interior, the 350 watt lithium heater in the rear trunk keeps the entire coach at around 45 degrees, eliminating a need for winterizing. In the image below you can see the open area on the firewall where it vents to the coach.

Regards - Mike

[InterBlog]

Originally Posted by hbn7hj

As you can tell we really aren't too interested in your system. No one here that I know of has chosen Lithionics. No one is interested in charging an 800AH bank with an Onan.......

This thread is like a big fish that launched itself into our forum canoe, thrashed around on the bottom of it for quite some time, then lay still, at which point we thought, "Whew, it's dead."

But then, like fish sometimes do, it began flopping anew, in an abrupt and startling way.

This image below was not cross-posted to this thread originally, and does not incorporate the responses posted after I created this image below. But the subsequent responses were much in this same vein.

Just to emphasize hbn7hj's point about HOW THOROUGHLY van owners are not interested in charging a lithium battery with an Onan, here are our system comparisons:

[IdleUp]

My apologies if the concept of my "Advanced Lithium RV" is too difficult for some to understand. The reason I've been successful in the aviation drone field is because I always strive to stay ahead of current technology, this is the reason my lithium RV is unlike any other and works on advanced principals.

I've since been out on a dozen "off the grid" trips and the system works as planned, my last post of my trip to Ohio is testimonial of that!

In any case, there has been well over 4000 who viewed the production on youtube and my server and other sites, I've received hundreds of text and emails not only from RV owners but from many corporations thanking me for taking the time to document the installation. In summery, I feel great the film has provided needed information to other RV owners.

Mission Accomplished!

Regards - Mike

P.S Onan? Did you watch the video - I haven't started my generator in 6 months!


[/SIZE]

[booster]

You know some will never let this rest as thhe always needs to be "right and best"!



Better to just let the trolls crawl back under the bridge than to feed it, I fear.