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rt66gv 03-04-2013 07:15 AM

Accurate way to estimate EV range?
I finally got all my new deep cycle, lead acid batteries (13, 12-volt, 156 volt system) for my Solectria Force.

I'm trying to get an idea on range once the batteries are broken in. Original specs on the car say 70 miles, and I'm pretty sure it didn't have 114 Amp Hour batteries (like it does now) when it was new.

However, online range estimators are only saying about 45 miles roughly. The car is very light and only uses 140 watt hours per mile at 35 MPH and 200 watt hours at 45 MPH.

Any thoughts? Does anyone know of a very accurate way to approximate range so I don't damage the new batteries? Just curious, it might be a trial and error thing til I figure it out.

MetroMPG 03-04-2013 08:15 AM

If your goal is avoiding damaging the new batteries, the best advice is to monitor them while driving, rather than estimate a range and "hope" it's correct.

You want to avoid drawing a 12v lead acid battery below 10.5 volts under load -- a.k.a. the battricide zone.

You should get a Pak Trackr or similar.

I use a DIY LED bar graph to keep an eye on (avoid murdering) my small 48v pack:

MetroMPG 03-04-2013 08:17 AM

PS - I've driven a Solectria Force sedan. Fun, slick EV!

hamsterpower 03-04-2013 09:43 AM

a rough estimate is :
volts(156) x amp hour(114) = total watts(17784)-50% safe usable range for lead=(8892)/ watt per mile(200) = range 44.46 miles @45mph.

Of course monitoring is better than estimating.

TheSGC 03-04-2013 10:03 AM

I've been working with Solectria's for the past few years and you are not going to get 70 miles on lead. The NiMH forces got 70-100 miles per charge, but the with lead acid you're lucky if you get past 50 miles, usually 40 miles was the norm.

rt66gv 03-04-2013 10:05 AM

Thanks MetroMPG for the input. I should have explained in more detail as I'm not exactly guessing. I've taken the 12.8 volts, which is a full charge per battery, and multiplied it by 13 batteries for 167 volts at full charge. I did the same for an 80% discharge (the max recommended) for roughly 160 volts. I then made up a digital fuel gauge to hang from my rear view mirror, so to speak, with voltages at full, 3/4, 1/2 and 1/4. I'm using my digital multimeter to determine state of charge when I'm stopped and all lights, accessories, etc. are turned off. This is the most accurate way I could think of to monitor battery capacity. I only wondered if there's a better way (that doesn't cost a small fortune) or if my method is pretty good.

TheSGC 03-04-2013 10:33 AM

The best way is use both voltage and AH counter. Just make sure that 10.5v (under load) is considered "dead" when using a volt meter.

I had a PakTrakr to monitor my lead acid pack and while it had a built in State of Charge meter, I usually used Voltage and made a cheat sheet of different SoC and their corresponding voltages.

Cobb 03-04-2013 12:30 PM

As a former electric wheelchair user, the answer is NO. Your best bet is to join AAA Plus for the towing so if you push your luck you can get towed home before you screw up your batteries. Just limit yoru trips in room temperature weather til you get a feel, plus it will take 12-15 cycle sof charge and use before the pack builds up.

Id suggest using it to just go to your local 711 to buy smokes, lottery tickets, etc, then after 2 weeks of doing this and plugging in try going further as you actively moniitor the charge/voltage. If it gets too low, dont wing it, park and have it towed. :eek:

Ryland 03-04-2013 07:05 PM

For longest battery life you don't want to draw the batteries down past 50% DOD so that leaves you with 30% buffer to draw them down to 80% DOD, so you will never be stranded!
I wouldn't bother trying to figure out your state of charge with your batteries at rest because while you are driving you are putting a higher load on them then they were really designed for so you really do want to know that voltage while under load and also watch how quickly that voltage bounces back up, but after you remove all loads it will keep climbing for an hour or more! but if you get your pack voltage to low while under load, that is where you do damage and it doesn't matter if your pack is fresh off the charger or if you are at the end of your trip.
As HampsterPower pointed out, at 45mph, under IDEAL conditions you have a 44 mile range, that is 80F battery pack, one person in the car, good new batteries, no strong winds, so making a trip that you can charge up as soon as you get there that is 40-45 miles on a nice summer day might be reasonable, but I would not do it every day if you want your pack to last more then a few years.

I average 10 to 15 miles of driving per day and charge at work and my pack will be 4 years old this summer and I seem to have a 30 mile range where 40 miles was what they said it was when my car was new, but people who drive cars like mine 30 miles per day are lucky to have their battery pack last 3 years.

rt66gv 03-05-2013 06:51 AM

Thanks for the answers, but I'm deleting the post. I'm going with my original idea I gave to GM back in the 90's that they told me wasn't feasible, yet they now sell the Volt for over $40K. I had the idea decades ago to have a small, onboard generator for unlimited range. Since my charger allows the car to be in motion while being charged, I'm getting a small, lightweight trailer hitch to mount my generator to. It only weighs 60 lbs. and runs 10 hours on a gallon of gas. So, at only 40 cents per hour if and when I need the generator, I'm still FAR better off than with my gas car.

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