I've been impressed with the depth of knowledge and thoughtful conversation on the Forum - so thought I would throw out my idea for an 'all electric' camper van build that I had been thinking of building.
The Idea
I'd use diesel or gasoline for cabin heat (Espar or Webasto type) with the goal being a 'single fuel' vehicle (no propane). Water heating, cooking (inductive cook top, microwave, and toaster oven), cooling (optional A/C), fridge, and all kinds of other accessories would be powered good old 110V AC. This would be enabled by a 2.5KW or possibly 3.5KW 48V DC power inverter with a bank of 14 Serial 5 Parallel (14S5P) NCA (Li-aluminum) 18650 batteries - 52V nominal voltage with a charge voltage of 58V. The battery banks will all be inside the heated part of the van and each group of cells will be protected with a BMC (battery management controller). There would still be a smallish AGM 12V cabin battery to handle the things that are not big power drains - this would be charged by the engine's alternator and (optionally) a solar system.
Advantages of this approach
* Simple design: Using mostly 'off the shelf' 110V appliances would save hundreds of $$ which could be used to fund the slightly more expensive battery bank. Appliances would be easily installed using common household wiring within the van. Much easier than routing propane, fitting tanks, and dealing with hazards like open flames. Plus, everything switches over to shore power easily. Lithium batteries are much smaller and lighter in terms of energy density than lead acid, so they can easily be placed into nooks and crannies on the interior of the van rather than locating a large bank of lead acid batteries inside or under the van.
* Lower Cost: Many people seem to think lithium is expensive. Many the current offerings offered by new high end RV makers are expensive, but I think a lot of those costs are due to an in-efficient design rather than inherent costs of lithium. I'll break down some cost estimates below, but my estimates show a very capable system for much less cost.
* Better Reliability: RV appliances are complex, usually because they are designed to operate with various types of power (110V, 12V, and sometimes propane). Standard 110V appliances are very common and easy to service.
*Peace and tranquility!: No annoying generators to deal with. Silent appliances. Fewer systems to manage.
Cost Estimates
First I'd bring up the subject of 'usable power'. Lithium has a big advantage over lead-acid in that you can reliably use at least 80% (or more!) of it's capacity. For longevity reasons, I only run my lead-acid batteries to 50% state of charge. So for argument sake, if I have 200ah of AGM installed; I would call that 1.2KWh of 'usable power' (200Ah * 12V *.5 = 1,200Wh). By comparison, my 14 Series 5 Parallel (14S5P) Lithium bicycle battery would have approx 696Wh of 'usable power' (50.4V * 17.25Ah *.8 = 695.5Wh).
So if my minimal system would require the equivalent of about 400Ah of conventional lead acid house batteries; I could build that with four of my bicycle batteries.
* 400Ah of Lead Acid usable power ~= 2.4KWh usable
* Four of my 14S5P Lithium batteries ~= 2.78KWh usable
My bicycle battery is built with 70 Panasonic 18650 GA cells. These are great cells, that have good capacity and provide lots of current per cell (10A / cell).
For the campervan application I would use the LG F1L 18650 cell or a similar NCR style battery since it's lower cost and has great capacity. It just doesn't support high drain applications (only about 5A / cell), but should be fine for this.
The 2.8KWh battery would require 280 cells total (4 batteries of 70 cells each), 4 bms boards, various nickel weld strips and battery holders, and several hours of labor.
280 cells = 280 * $3.78/cell = $1,059
4 bms boards @ $27 each = $108
Nickles stips, battery holders, shrink wrap, solder, etc. $25
So the Lithium battery would be about $1,200.
Four Group 31 AGM batteries; Trojan 31-AGM's (100aH) are listed at $270 ecah online.
4 100aH batteries = 4 * $270 = $ 1,080
This Lithium battery would only be 11% more expensive than the AGM equivalent (assuming your labor was free). However the Lithium battery is expected to last many more cycles than the AGM battery. When you factor in the lighter weight and smaller size; the lithium battery looks really good.
Here is where the idea really shines. Say all of these appliance require much more power. You could double the 'usable power' for another $1,200 or even triple it for an additional $2,400 and still manage to find places for all 12 of these batteries inside. Locating 12 of the heavy AGM batteries in the van would be hard and really weigh it down.
Inverter: I'd consider the COTEK 3500 Watt 48V PSW Inverter with Transfer Switch for $1,100. Having the x-fer switch for shore power integrated makes a lot of sense. This inverter would probably do the job for the loads mentioned above plus occasional A/C when used carefully (not at the same time as other heavy loads).
https://invertersrus.com/product/cotek-sd3500-148/
I think this inverter would only be $2-300 more than a good 2,000 Watt inverter that you would probably buy anyway for a campervan.
Other cost factors:
*
Inductive cooktop: ~$75 vs ~$150 and up for propane cook top
(Then think of all of the cost and complexity of adding propane)
OR: a diesel or gasoline cook top - but that will add around $1K
*
Water heater: $160 for a Bosh 1400W 4 gallon electric vs $430 (and up!) for an Atwood 6 gallon propane (with electronic ignition)
*
Fridge: Small residential fridge ~$150 vs ~$800 for a 12V/110V compressor fridge.
Charging:
This is more complicated. Ideally, you would like to be able to charge the big house battery quickly. But that is not that easy, especially when boondocking.
I've been thinking of two solutions for this, both have their tradeoffs;
1. Easiest: Get the truck with the biggest alternator you can. My Promaster has a 220A alternator and I think you can get similar ones for the Sprinter and the Ford Transit. Then connect a basic high wattage inverter to heavy cables like this one;
Aims 3,000W inverter $280
https://invertersrus.com/product/aims-pwrinv300012120w/
From that you can run standard 110V battery chargers for the Lithium batteries. So for my example, I would need 4 14S Lithium battery chargers ($100 each). The charger below would charge this battery off the OEM alternator in just over 3 hours. Not great, but probably workable.. Because these batteries scale, if I had twice as much battery; I would just need 8 of these chargers rather than 4 and it would still take about 3.5 hours to charge.
https://lunacycle.com/batteries/char...ebike-charger/
So this 'easy' solution would cost me about $680 to $1,080 depending on the size of the battery.
2. Harder ( but cooler!) solution: Add a second alternator that was just for charging the big Lithium battery - like the Hymer underhood generator. But unlike Hymer, go the route that Advanced RV did and run it at a higher voltage. There are two challenges here. First getting a bracket for the 2nd alternator and fitting it. Hard, but not too hard. Second, sourcing a high DC voltage alternator. These are not common. I think the voltage regulator could be be modified on a good quality 'commodity alternator to create a 58V DC output. This is a topic I have looked into for a while and think it's worthy of a whole separate thread. But if you think about it, a 100A alternator would be producing 5.8KW! That's a lot of juice! You could charge your battery quickly and still have power to run your inverter. It's spec'd to handle over 60V.
Price for this solution is TBD. But it shouldn't be much more than the simple solution above. Bracket, commodity alternator, and the hard part - custom voltage regulator.
Battery Chemistry
Almost every Lithium RV example I've seen to date is using Lithium Phosphate LiFEPO4. I understand why they do this; they are trying to mimic the traditional 12V Lead Acid battery. The primary advantage is to solve the charging issue. But as I demonstrated above, you can still address the charging issue with an inverter and 110V charger (not pretty, but it works). Many go with the 2nd alternator anyway, and there I think it makes more sense to go with a higher voltage. Once you make that decision, the cell voltage no longer matters.
NCR batteries are superior to IFR batteries in so many ways I just don't see why you would choose them.
Safety
One of the topics that always comes up with new ideas is safety, and for good reason. We've all heard stories of exploding Lithium batteries. What could be worse for an RV application? What about exploding propane tanks? Or the silent killer, Carbon Monoxide? While it's true that the Lithium cells can be volatile; it's almost always due to over or under charging. This is what the BMS addresses. Therefore, I think it's better to have a NCR battery protected with a BMS than an unprotected IFR battery (and I've seen this).
The other issue is a pierced or ruptured battery. Though this can happen, the only videos of really violent explosions that I've seen usually involve overcharging the battery way above it's limit (and modern ones don't explode when this happens by the way), then piercing it with a shop press. Piercing a battery with a standard charge doesn't result in much of a show. Given the way that I would place the batteries in the coach, I wouldn't expect them to be pierced any more than I would expect a propane tank to be ruptured.
I can't think of a single electric car that is using IFR batteries. These cars are moving around *much* bigger batteries that are far more exposed than the proposed RV battery. If collisions were such a threat for battery explosions, you would hear a lot more about this.
I've been riding my e-bikes off road in very harsh conditions and then charging them back up in my camper van. The batteries have been in very rough conditions and all kinds of weather and have held up remarkably well.
I think the lithium battery would make an awesome camper van. What are your thoughts?
A unique Li-ion Campervan Build..
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