doubled ev range less then $2500 no car modifications

doesn't it cost the same to rack a 70w panel as a 270w panel ?

 

so if racking a 270W panel costs 15 cents a watt, $40, racking a 70w panel at $40 costs 58 cents a watt. The racking costs more than the panel.

 

I think you've got the right idea John. $/watt is not a very good way to estimate racking cost, particularly when comparing laminate/thin film and crystalline. Racking cost is dominated by # of clamps, # of attachments and linear footage of beam required. I recently bought a palette of Canadian Solar CS6P-230Ps from the same vendor to build a 5.52kW gridtie system at home. These panels put out 230W for 982mm of width. The 70W laminates use 600 mm of width. So you'll need (230/982) / (70/600) = 2.0 times as much linear footage of beaming. Number of attachment points scales roughly with linear footage, so 2X the number of standoffs/attachments. You'll also need >3X the number of panels for a given capacity, so ~6X the number of clamps.

At $1/W I was basically even after racking costs going with the Canadian Solar even using Unistrut, which was less than half the best price I could find on Al racking. Was glad to discover that, as I didn't have the sq footage for the laminates anyway. Think laminates were still more like $0.79/W when I bought though.

Rob

 

I certainly wish you luck with that. Gels can last longer than AGM, but tend to be twice as finicky.

Rob

 

Hm, if I look at the buying just the components from Enginer that provide a comparable system to the AGM solution, the prices are comparable:
$1800 (2x 2kWh Li-ion batteries)
$200 (48V 15A battery charger)
$500 (AC inverter)
$2500 Total

Compared to the Portable Power Station, this excludes the case, extinguisher, BMS, and assembly (if I haven't missed anything).

There doesn't seem to be a BMS in the AGM solution; is it not necessary? Is the BMS necessary with the Enginer batteries?

 

No, for 3 12V AGMs (OP is using Gel Cells Technically) tied in parallel there is no need for BMS/balancing.

With the 48V Li pack from Enginer a BMS is advised to protect lifespan. Even with the additional $400 cost, the result is a much smaller, lighter solution that should last at least twice as long in terms of # of cycles based on >2000 cycles at 80% DOD. Need to be sure they are up to the current draw though. OP stated a max observed battery current of 360A. That would probably toast these batteries, which are rated for ~100A ea, or 200A total. However he shows a typical current of 12A AC, which would probably only be about 150A DC, or 75A per battery.

This 36V GBS 3.8kWh pack might hold up better, as its rated for 300A continuous, 1000A peak. It includes BMS, charger, and SOC readout, and costs about $2400. You'd have to find a 36V inverter though. Didn't see any after doing a quick search, other than a bunch of Chinese ones. Possible Enginer could source one or possible the existing one can be set up for 36V.
http://elitepowersolutions.com/products/product_info.php?cPath=27_36&products_id=200

 

I think novasolar was referring to energy, not current.

At 12V, that's 4.35kWh and assuming it's 3.3kWh to charge the battery, that's ~75% efficiency for the AC inverter which is a bit less than the >80% spec.

 

What about taking a high voltage battery like the PIS, adding a 16A current limiter, then attaching it to the OEM battery like the way Enginer does? I'm not sure how much the current limiter would cost, but it probably costs less than $1500 controller board. The system would be relatively small, consisting of just a Li-ion battery pack (w/ BMS) and a current limiter. It would provide some additional power during driving, like Enginer and allow recharging of the OEM battery pack if parked and left on.

 

Its certainly doable, but I'm not sure it would have any advantage over the existing Enginer kit. The dc:dc converter does two main things. Throttles current, and converts battery voltage to the system voltage. Once you have a dc:dc converter, to the first order it doesn't really matter what the battery voltage is.

Rob

 

You are quite right, that's where I was getting confused. I saw 360A not 360Ah. If thats measured out of the 12V battery, then the 75% is the combined efficiency of the AC inverter and the Prius charger.

With that number, it looks like neither the 2X Enginer battery or 36V GBS pack would have enough capacity to overcome the combined inefficiency of the inverter/charger. You'd probably have to step up to something like the 48V / 5.1kWh GBS pack here at ~$3100.
Elite Power Solutions

Its also worth noting that the OP is using a "true sine" inverter, whereas the 48V inverter from Enginer is a modified sine. That could cause problems for the PiP charger.

Here's an example of a 1500W continuous true sine 48V inverter for $529.
COTEK SK1500-148 1500 Watt 48 Volt Pure Sine Wave Inverter - High Surge

The combined inefficiency of the inverter and charger are definitely the downside to this approach. In that sense using something like the standard Enginer kit to recharge directly by dc while parked seems like a better option, particularly if someone can figure out how to do it without having to leave the car "running." It would seem like there must be some way to do this, as the PiP must have a "charge mode" that enables it to charge from the wall while powered off. I don't know that anyone knows enough about the mechanics of how this is done to speculate on a solution yet though.

IMHO figuring that out might make the Enginer kit much more attractive for the PiP, at least for those with an appropriate driving cycle.

Rob

 

While there's no advantage in terms of the power provided during driving, I think the system would be smaller making it easier to remove to regain all the cargo space and minimizing the reduction of cargo space when it is installed. In the Enginer kit, space breakdown is approximately:
1/2 battery
1/4 DC/DC converter
1/4 BMS + battery charger

The PIS kit has the BMS as part of the battery pack and this is about the size of the Enginer battery. With just the addition of the a current limiter, I think it would be 60-75% the size of the Enginer kit. The PIS battery pack + BMS cost ~$3000. Add in the cost of the current limiter and I think it's comparable in cost to the Enginer kit.

 

Yep, I was thinking that direct DC charging while off would be cool as well. But since it currently does not exist, I was trying to figure out a compact, light weight, affordable, easily removable, and simple method with what is currently readily available.

 

My initial calculations were based on incomplete info, and a mistaken reading of your initial report as a battery current of 360A rather than 360Ah. So now that we have a bit more info, I can repeat the calculations alittle more accurately.

The first big challenge in using lead acid batteries is whats referred to as the Puekert effect. Basically, the higher the current draw on a lead acid battery, the lower its effective capacity.

Peukert's law - Wikipedia, the free encyclopedia

The second challenge is that the data reported by manufacturers tends to under fairly idealized conditions, and vehicle applications tend to be a pretty non-ideal environment. The data given is often not sufficient to estimate real world performance, so certain assumptions have to be made.

I think it was a smart choice to go with 3 batteries in parallel, even though an ideal calculation would have indicated that two might have been enough. Spreading the current draw evenly over 3 batteries results in 122 / 3 = ~41 Amps per battery. The linked datasheet includes only a C/100 and C/20 capacity. C/100 is 250Ah/100hrs = 2.45A discharge, and C/20 is 245Ah / 20 hrs = 12.25A discharge current. Based on that info, we know the capacity will be less than 245Ah at 41A, but we can't really estimate what it will be. This info sheet on the MK AGM family gives perhaps a clearer picture:
http://www.civicsolar.com/sites/default/files/documents/8115mkagmlgv2r5-42916.pdf

The closest data point is the 230 minutes to discharge at 50A for the 8A8D "250Ah" battery. At this current, the effective capacity is 50A * 230 min / 60 min /hr = 191.67 Ah. So the bank of 3 batteries will have an effective capacity of 575Ah, rather than the expected 750Ah. Not terrible considering the high current draws in EVs often reduce the capacity by a full 50%!

So lets assume 122 Amps for 2hrs to begin with. That's 244Ah / 575Ah or 42% DOD. Depending on the taper current for the final half hour, the final result may be close to 50% DOD. If your earlier measured value of 360Ah total was accurate, 360Ah/575Ah = 63% DOD. Based on the chart on the datasheet, cycle life should be about 400-600 cycles at this DOD under ideal conditions.

The next challenge is that these numbers are only really good for the laboratory conditions of 77F. The last page of the family info sheet shows the effect of temperature on capacity. Your case is similar to the middle curve, 4x I20 as 41A is closest to 4x12.25A, rather than 1x or 10x. The bottom of that middle curve range shows the effect of discharging and charging at the specified temperature, which I assume will be your case. The curve starts at ~85% of nominal capacity for this current. So at 0C/32F, capacity will be reduced to 70%, or 70/85 = 82% of effective capacity. At -10C/14F, capacity is reduced to 58%, or 58/85 = 68% of effective capacity. At -20C/-4F, its reduced to 43% or 43/85 = 51% of effective capacity.

So the effective capacity and DOD vs. temperature would look like:
0C: 0.82*575 Ah = 472 Ah, 244 to 360Ah / 472Ah = 52 - 76 % DOD
-10C: 0.68*575Ah = 391 Ah, 244-360Ah / 391Ah = 62 - 92 % DOD
-20C: 0.51*575Ah = 293 Ah, 244-360Ah / 293 h = 83 - 123% DOD

So winters will tend to be pretty hard on your battery, running it to deeper depths of discharge and shortening their cycle life further. If you can charge indoors, like in a heated garage after giving the batteries time to warm up you can get back ~5% of the battery capacity which helps a little. Also of concern in this realm is the variation of charging voltage requirements over temperature indicated in the bottom right graph on that same page. To effectively charge at different temperatures, the charge voltage used must be compensated pretty substantially. Some chargers do this automatically, but the profile needs to be programmed to match your batteries. I don't believe most cheaper chargers do this at all. If you are lucky they may let you adjust the output voltage so you can manually compensate. While the 20C nominal charge voltage is 14.4-14.5V, at 0C its 15.1-15.2, and at -10C 15.5-15.6 and at -20C about 15.8 to 16.0. If the charger is set to output a fixed 14.5V, it will substantially undercharge the battery at low temperatures which is very bad for the cycle life. Both because then you will effectively discharge the battery to an even lower DOD because you started at less than 100% SOC, but also because the top end of the charge cycles in a Pb battery is what tends to "refresh" the electrodes to maintain cycle life. If your charger isn't temperature compensated appropriately, that's probably another really good reason to try and charge at room temp if you can.

Lastly, capacity of Pb batteries tends to degrade over their life. In an EV this means less range. In an application like this it means you are always having to discharge the batteries a little deeper over time to get the same amount of power out. This effectively starts to accelerate the aging process the more cycles they've been through.

I'm not trying to give you a hard time, like I said earlier I think its a really creative solution to the problem. I've just seen a lot of people in the EV and PHEV communities over the years get tempted by the apparent lower cost of lead acid batteries only to be really disappointed.

Since they don't suffer from the Puekert effect, a Li battery pack could be sized smaller than the Pb pack. With a ~5kW pack, you'd probably still get 80% DOD and 2000+ cycles. So even though it might cost a bit more upfront, particularly if you factor in a BMS, over the long run they may actually cost you much less.

At 12V, you can probably get away without a BMS. So 4 of these 100Ah 12.8V GBS Li cells would probably do the job at ~$2480.
Elite Power Solutions

A 48V kit with 4 of the same 100Ah batteries plus a matched charger and BMS is ~$3100.
Elite Power Solutions

Rob

 

Here are a couple more pics novasolar wanted to post:

 

i don't know if there is a warranty on cycles.

 

No problem. I hope you don't take my comments as being critical. As I said I'm very impressed with what you put together. Its a very creative solution to the problem. I just know that lead packs have disappointed a lot of folks in the past.

Most of the Li packs you can buy won't have that kind of warranty. You'll only get that if you buy one as part of a car from a manufacturer, as they are required to warranty it that way because its considered part of the emissions control equipment. As a result they put a lot of work into testing and creating a control system to make the batteries last that long. Battery manufacturers are often hesitant to offer warranties as their life is so dependent on how you use them and treat them. Most lead acid manufacturers that have a warranty won't honor that warranty for EV type applications because its a harsh environment from what I've heard.

The GBS packs offer a 1 year limited warranty when you buy the batteries, bms and charger all together, not sure if you get than on just the cells alone. Enginer offers a two year warranty on their battery pack. The A123 pouches that some folks have been using are a great deal for the performance, but carry no warranty as they are basically "grey market." CALB cells are also popular, and seem to have a 1 year warranty.