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Old 12-25-2016, 01:45 PM   #1
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Default Solar Class B

Who says Class B's have to run on fuel.

This 'zero fuel' electric VW bus conversion features its own rooftop solar array : TreeHugger
Phase Two
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Old 12-25-2016, 02:56 PM   #2
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His solar charging rate numbers don't add up, and neither do his shore charger claims. He can't charge the batteries in anywhere close to the times he claims, especially with them as wet cell.

1800AH @ 12v (doesn't say operating volts so all calc are at 12v equivalent). 1020# of batteries. What is the load capacity of a VW bus?

1220watts of solar will give about 420AH per day based on optimistic 35AH per day per 100 watts. Not even close to recharging in just over a day, even if he gets double that much by some magic.

2.3 hours of shore charging with a 40 amps of shore charger would give 92AH at 12v charging voltage, 184AH of 12v at 24volt charging voltage, 368AH at 36v charging voltage, 736AH at 72v charging, 1472AH at 144v charging (still 12v equivalent). The 1472 12v AH would get them from 20% to 100% full if the acceptance was there, but it is not. They are going to need at 4-6 hours longer than the 2.3 hours to get full, even with 40 amps of 144v charging, from 20% SOC. It would also be at about 30% of capacity charging on wet cells, which will kill them quickly due to heat. 1472AH at 12v in 2.3 hours needs 640 amps, 7680 watts, which takes 66.8 amps of 115v AC at 100% efficiency, so no shore power is big enough, unless he is running 50 amp 220v input.

I think maybe he is the guy from Roadtrek that did the original etrek charging and AC running specs, as they seem to be exaggerated by the same amounts

As always, calc checking is welcomed, as I blew through it pretty quickly.
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Old 12-25-2016, 03:39 PM   #3
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Old 12-25-2016, 04:56 PM   #4
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A couple of considerations:


1. Possibly the 40 amp chargers are input value which would give closer to 400 amps X Efficiency at 12 volts. 2 would give 800 amps X efficiency. (80% would give 640 amps) They could be powered from 2 sides of a 50 amp 220VAC RV Park connection (Provided, of course, that the park would permit it!, and the batteries could take it without blowing up)

2. Other electric cars (Tesla, Chev Bolt and golf carts and fork lifts) can certainly charge overnight, although they might use different battery chemistries.


3. A 144 volt connection is the most likely because there are motors and controllers commercially available for these voltage levels.

4. I would agree that the solar is probably not a major player in this scenario, but it could provide an assist during driving on sunny days and probably increase the range.

5. He has probably removed the engine, gas tank and transmission to drop weight.

My thoughts anyway. FWIW.

John
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Old 12-26-2016, 01:22 AM   #5
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A couple of considerations:


1. Possibly the 40 amp chargers are input value which would give closer to 400 amps X Efficiency at 12 volts. 2 would give 800 amps X efficiency. (80% would give 640 amps) They could be powered from 2 sides of a 50 amp 220VAC RV Park connection (Provided, of course, that the park would permit it!, and the batteries could take it without blowing up)

2. Other electric cars (Tesla, Chev Bolt and golf carts and fork lifts) can certainly charge overnight, although they might use different battery chemistries.


3. A 144 volt connection is the most likely because there are motors and controllers commercially available for these voltage levels.

4. I would agree that the solar is probably not a major player in this scenario, but it could provide an assist during driving on sunny days and probably increase the range.

5. He has probably removed the engine, gas tank and transmission to drop weight.

My thoughts anyway. FWIW.

John
It wasn't stated as two 40 amp chargers, it was stated as two 20 amp chargers., and having the charging at 144v, as in my last example would give more charging power than the same amps at 115v input, so they would have to at 220v input to be higher than that.

Yep Tesla can charge overnight with high acceptance batteries that don't taper and need many hours to finish charging. The link stated 2.3 hour to fully charge, which is virtually impossible from and state of charge lower than like 95% with wet cells, no matter how big your charger is. 40 amps of 220v is available in some campsites, but very few homes or other sources, and often not in less than fancy campgrounds that cater to big class A's. And, as stated, even at 40 amps of 220v, he can't fully charge in 2.3 hours.

Removing weight is not going to speed up charging, only range, and my calculations addressed exaggerated charging and recovery times, not range. It could help offset the very large amount of battery weight, though.

My intent is point out the exaggerations so folks don't get the idea that those kinds of results are typical, or even possible. We saw lots of confusion when Roadtrek did the same type of thing, spreading lots of bad information about big battery, off grid, capabilities. It also points out that the linked site person did not actually test any of the system to confirm his calculations, and is merely reporting what he thinks he should be getting.

I think it is great to see people pushing the envelope with stuff like this, as it helps all the tech move ahead. But, along with the doing it, I think it is equally important to try to give accurate data on how it all turns out, like Technomadia does, to keep others from doing the same things and getting unexpectedly bad results compared to what was published.

I hope the linked poster does follow up with results and conclusions, after more use. I think it could be very educational for a lot of folks.
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Old 12-26-2016, 01:36 AM   #6
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I agree. Faulty or exaggerated data does no one any service. Any claims must be backed up by solid data takes by properly calibrated instrumentation. Anything less is just hot air and leaves one open to all kinds of guessing and conjecture.

John
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Old 12-26-2016, 02:48 PM   #7
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There is a lot more technical information here:
About Us
It should answer part of your questions.
William
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Old 12-26-2016, 04:24 PM   #8
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More information there, for sure, but he is still not really doing what he thinks, and says, he is.

His 5000 watts of chargers is equivalent to 416 amps at 12v, so in 2.3 hours he could put in 956ah at 100% efficiency, or 860 at 90% which is more realistic.

At 10 amps of 110v charging input, 1100 watts, would give 92 amps at 12v. He would get 920ah in the 10 hours stated at 100%. 828ah at 90%.

He says he is getting about 80ah per battery out of 150ah batteries due to his heavy loads (.3 up to 2C) and Peukert, going to 20% SOC. He doesn't define how he is determining the SOC, which is the critical thing here. If he is using voltage, it will need to be different at different loads, so he would have to chart relating the loads vs SOC (determined by checking the specific gravity). If he is checking the specific gravity, he will know what his SOC is, and is really the only way he has to know anywhere near accurately, I think.

We have learned on other Peukert threads on this forum, that batteries don't have less energy to give up if discharged at higher rates. They just get to the arbitrary "empty" cutoff voltage of 10.5v(?) at less ah taken out of the battery. If you check the specific gravity after a bit of rest, the battery will show it is at a higher state of charge than Peukert would say. If he is cutting off at 20% SOC based on Peukert adjusted voltage, he is actually at a substantially higher SOC than the 20% if the loads were fairly high.

Here is where things start to come apart on his numbers. He says he gets about 80ah per battery out to get to 20% SOC, which is 960ah or 53% of the commonly used 20 hour rating he quotes for his batteries. So if his batteries are truly full when he starts, his actual SOC is 47% based on the 20 hour rating. He just is using actual SOC terminology instead of usable power available before cutting off with 20% usable left. For his power use, this is just fine, as it is what matters, and I have no issue with this at all. What is the problem is that if his batteries were truly full, and pulled down to 47% actual SOC, he would need to put his 960ah plus charge efficiency back into them to get full. His chargers are capable about .233C charge rate, or about 35 amps per battery. This would get him to 70% SOC in about 1 hour and at that point the batteries are going to start tapering acceptance very quickly and in the next 1.3 hours probably get to no more than about 85%. If you look at his 2.3 hours to fully charge claim, it comes right out at 35 amps from the charger for 2.3 hours equals the 80ah per battery he used. This means 100% charger and charge efficiency (impossible for both) and no tapering of acceptance, (meaning all the charging was done at full acceptance and that would mean the batteries never got over about 70% actual SOC. He doesn't say if he measures the ah back in or not, but I assume he does.

The ONLY conclusion that can be made for his numbers to work at all, is that his 20% SOC probably is correct and is what the specific gravity would say it is (based on 20 hour rate). When he uses 80ah, he is using 53% of the actual capacity ah, so that is likely correct. To be able to get those 80ah back in 2.3 hours, the charger would have to at full output and the batteries at full acceptance, so under 70% all the 2.3 hours.

All this really means is that he is cycling his batteries between 20% and 70% state of charge, and he doesn't understand how Peukert works in cases like this. At the high discharge rates he is using, and with the batteries rarely if ever getting totally full on regular basis, he will likely have quite short battery life, compared to what he could have if they were fully charged regularly.

Of interest is that when he charges at 92 amps for 10 hours, he recovers less total ah than the fast charger does, but says he gets more travel distance from them. This would point out that the big charger is tapering some due to battery acceptance, even on a deep discharge to 20% and he is not getting his full 35 amps the whole time. The 10 hours allows him to recover more because of the hold time during tapering of charge amps due to battery acceptance rates.

This also means that neither charging source is even replacing what he used, 960ah, as the sources provide 960 or 920ah respectively in the times he states, and efficiencies will drop those numbers by over 10%, most likely to 864 and 828ah, or lower.

He does stand a chance of truly getting his batteries full if he sits for a while, either longer on shore power or with the solar. The solar, he states will do a theoretical max of 8 amps at 150v so 1200 watts in perfect sun 100% efficiency. He would get 80ah per battery in 10 hours of perfect (high noon type) sun and 100% charge and controller efficiency. Not likely to get all he used in a 960ah drive use, but in two days or more of very good conditions might make it depending on other uses. Using the solar for a day after using one of the other charging sources would also be possible (this is what a lot of us do with our solar, using it to top off lead acid batteries after a short, very high rate, engine generator run to get to 80% SOC or so).

I certainly don't want to belittle his efforts, as I think it is a pretty cool thing he has done, and if he had used the lithium batteries that he thought about, a lot of the things he says would work out pretty closely because of their very low voltage drop and high acceptance rates during charging.

What is badly missing in his statements is the understanding of how Peukert actually works in applications like this, and how devastating the lead acid battery charging profile, and need to get totally full regularly, can be on a high load, high use, rapid recharge needing, battery system.

He used the very commonly done, in error, charge time calculation of amp hours needed to charge, divided by max charger output, to get his hours of charge time, which is only even close in very discharged batteries and only for a short time of charging. He also ignored charger and battery charge efficiencies, which throws it off even further and can quadruple charge times needed to get fully charged.
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Old 05-19-2017, 05:51 AM   #9
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Youtube video with explanation of his setup.
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Old 05-19-2017, 02:20 PM   #10
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50 mile range? That is hardly enough range to travel from the (Big Bend National Park) entrance to the campsites!
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