# EV Display - Customer review thread



## jtgreeson (Aug 14, 2009)

Here's some photos of my installation progress:










This shows the display and sensor as received and the face of the instrument I wanted to install it into.














This shows my bus bar progress. Top bar was the original bar from TS. Center bar was made out of a 6 in length of 1/2 in copper tubing bent flat and folded over once. Heat from propane torch made it easy to form. Even though it did fit in the sensor hole I thought it didn't have enough cross section. The bottom bar was made the same way but I added another length of 3/8 tubing inside of it and made a "sandwich". Final dimensions were .55 in by .2 inch. If I figured it right, that comes to .11 sq in which is 71 sq mm. I wired the car with 2/0 cable which is 67.4 sq mm so I think it's good. As a reference 1/0 cable is 53.5 and 3/0 is 85 sq mm.













Final configuration, it just fit.

















Sensor sitting pretty on top of my 180 Ah TS bank in the front of the vehicle. I added a little heat shrink to minimize vibration.























Sensor mounted.jpg


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## JRP3 (Mar 7, 2008)

JT covered the install pretty well, don't have much to add to that. The display was pretty easy to calibrate and gives a lot of options. So far I've been mostly using amps in and out, and Ah remaining display. It's nice to be able to check the pack temperature as well. I did have some issues with weird values but it was just an improperly seated data cable, user error  Make sure the connection is tight, "clicks in", and stabilize it from vibration and strain. 
For all it does I'm not sure there is anything out there comparable for the price.


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## jtgreeson (Aug 14, 2009)

I finally got some time at home to complete my installation. I mounted the guts of the display into my original instrument by cutting a hole and using silicone caulk to fix it in place. Here's some photos:

I made a mask to cover the rough cuts:













Here's all the bits before assembly:














Installed and working:














Finished instrument panel:












I've got just 15 miles and one charge using the gauge so far. It works! I'll try to post some info after I finish my initial evaluation.


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## JRP3 (Mar 7, 2008)

Looks great, how did you make the mask?


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## dtbaker (Jan 5, 2008)

are you guys using voltage scaler, or just monitoring 4 cells?


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## dimitri (May 16, 2008)

Dan,

I replied to your Email and pointed to related thread that Jim started here http://www.diyelectriccar.com/forums/showthread.php/need-circuit-design-help-dc-dc-47928.html

At this point my recommendation is to power EV Display from 12V aux battery and setup voltage display to always show your nominal pack voltage. This way the Watt and WattHour reading will be most accurate, with only 5%-7% error margin. 

EV Display's primary function is to track SOC by counting AH, and it does this very well. The rest was just a bonus and lack of precise voltage tracking should not be viewed as a fault, since its not a primary function anyway.

Hope this helps


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## dtbaker (Jan 5, 2008)

great info.... thanks. Sounds simple to power the unit from the 12v side of the dc-dc, no voltage scaler required that way. The watt-hr readings are a lot less important then the ah counter for safety of the battery pack. Typical use for me is usually a full charge every night, so a simple reset of the ah counter will take care of the small error from that last part of the charge cycle (<3amps). Any mid-day charge I get a chance to do and not finish would be at 10+amps so the Hall Sensor would read it and probably be pretty accurate.

Let me ask a tech question about temp compensation.... your unit has it which doubtless makes it more accurate than without. I am wondering how far 'off' ah count would be as temp varies from the nominal 75 degf?

My batteries will be enclosed, but I don't have any actual data yet as to what the temp is going to stabilize at under normal conditions, and/or how much of a heating system I am going to need for the winter.


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## dimitri (May 16, 2008)

Dan,

no need to reset the counter every day, its already compensated in the software and works well.

Since I am in Florida and I haven't gone thru "winter" with EV Display yet, I don't have concrete data for temp compensation. That is why I made it adjustable, so each customer can set it to what's most appropriate for their climate and their specific battery box/insulation situation.

Since cold temp produces deeper voltage sag on LFP cells, it means higher current will be pulled to get the same power level, which means AH tracking will catch it. So, I suspect temp compensation will not be as important as some might think. I suspect that default setting of 10% should work pretty well.

I'd be interested to get some feedback from people using the display up north thru the winter.


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## jtgreeson (Aug 14, 2009)

JRP: I made the mask on the computer using Adobe Illustrator. (any old graphics/paint program should work). I tried a couple of different papers to get the look I wanted. Settled on plain glossy photo paper. I think it came out good and not to amateurish. (I couldn't resist the "star wars" lingo though...too much fun)

dtbaker: I'm went with Dimitri's recommendation and powering it from the 12volt aux battery. I was gone a week from home and returned to a dead battery. The 2 amp fuse blew going to the contactor for the DC-DC so had no charge for the 12v aux. I'm still looking for the cause. The EV Display lost the SOC reading but retained the other battery parameters I had selected.


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## JRP3 (Mar 7, 2008)

I power mine from my 12 volt battery which is charged by my DC-DC. By the way, Dilithium is a Star Trek term, not Star Wars, for true nerd accuracy


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## jtgreeson (Aug 14, 2009)

Yep, just using star wars as a generic term. Since the motor is a WarP 9 I started labeling lots of stuff from Star Wars, Star Trek, Back to the Future, etc. About a dozen all over the guts of the car. It's real funny when someone asks "2 Gigawatts???" "Warp drive??". I'm having too much fun. Scotty, I need more power!


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## jtgreeson (Aug 14, 2009)

As of this date I've gone through about 5 charge/discharge cycles. The EV Display has worked well. Several observations:

1.) The lowest Amp it reads is 5. The operator's manual states that the sensor doesn't read low amps. When mine is right on the edge of 5 - 4 amps it just cycles between 5 and 0. (I don't know if that 5 amps is the lower limit or that's just the minimum the display shows)

2.) If you want to tweak your initial setting you have to depower the sensor. In an email to me Dimitri stated that is the only way. The SOC will reset to zero at that instant but will be accurate again the next time you fully charge the pack. (the "press both buttons" procedure only redoes the calibration) 

3.) I'm using 20% for my "min SOC" level and 5% for the "RelayLvl". That gives me a big red light on the dash (my "Energy Critical" light) at 25% SOC. That works out great for me and the family as a "time to be home" warning. Nice Work Dimitri for adding that.

4.) At 30amps charge rate the SOC gets back to 100% SOC about 30 minutes before the back is fully recharged. That's after 4 hours of charging. I'm assuming that's the 11% loss of efficiency due to charging losses.

5.) I've got my EV Display powered from the Aux bat. It's working well. The "xxxV Pack" display (Pack Voltage) is giving me a way to monitor my Aux Battery voltage. I just divide the indication of pack voltage by 12 and that's my aux bat voltage. (I have 48 cells) (example: "144v Pk" would indicate 12 volts)

I really like the display so far. Any comments from other users?


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## JRP3 (Mar 7, 2008)

jtgreeson said:


> 4.) At 30amps charge rate the SOC gets back to 100% SOC about 30 minutes before the back is fully recharged. That's after 4 hours of charging. I'm assuming that's the 11% loss of efficiency due to charging losses.


I found my EV Display was showing a bit more current going into the pack than my other meters were showing and also showed "full" long before the pack was full. I used the current compensation feature set to -10% and it's much more accurate. I've noticed that my clamp on meter tends to show more current if I clamp it on in the negative direction than the positive so it may be an inherent issue with hall effect sensing.


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## jtgreeson (Aug 14, 2009)

OK, That's interesting. So at 10% correction do you think it is more accurate reading during charging or discharging? How many amps was it off? I'll have to check mine. I don't have a clamp on meter so I'll have to hook up temporarily one that I have that reads up to 10 amps.


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## JRP3 (Mar 7, 2008)

I don't have a good way to measure amps out of the pack other than the EV Display, (the Curtis 840 display jumps around a lot), so it is possible that the -10% offset is under reporting amps out, though I have not run out earlier than expected yet. I'd have to do a deep discharge to check the amount of ah's used verses ah's reported. I'll have to do some full charges and discharges, see what sort of range I get, and see how much charge goes into the pack after the display shows full to know for sure.


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## JRP3 (Mar 7, 2008)

jtgreeson said:


> OK, That's interesting. So at 10% correction do you think it is more accurate reading during charging or discharging? How many amps was it off?


More accurate during charging and regen now, I felt it was reading around 10% high before.


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## dtbaker (Jan 5, 2008)

hhhmm, well the Hall Effect measurement is gonna miss low low amps either way, right? more likely to have low amps for the last part of charge cycle than discharge which is usually pretty high.....

the CycleAnalyst uses a shunt, but has other 'issues' and a not so spiffy display, but is an option I guess. Perhaps for pure amps in/out accuracy we need to ask someone to develop a SIMPLE 2" round amp-in/amp-out meter that is shunt based w/ temp correction and some calibration?


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## dimitri (May 16, 2008)

The problem is not the shunt vs. hall effect, the problem is to cover wide range of current given limited A/D resolution and limited precision of voltage reference components. This was a major design hurdle and I spent considerable effort to make it acceptable, yet keep it simple/affordable.

I specifically picked 600Amp sensor to cover medium/large EV conversions, but since the sensor is a 2 way device, its full range is 1200Amps. Even with 99% precision, that's +/- 12Amp error margin. I use Atmel processor which has 10 bit A/D conversion, which means 1024 possible values across the range, which means 1.2Amp resolution. When all these things add up it gets near impossible to accurately read the zero point, so you have to compromise and improvise. Zero point is absolutely critical in this device, so I have to drop the reading of small values, since those can't be trusted. Then I have to compensate on the charging side, that's why charging current reads 1-2Amps more than actual.

In reality, the end result is actually pretty damn accurate. I have collected ton of data during the design/testing to make sure the output is valid.

When you say it shows full 30 min prior to full charge, that's by design, to compensate for inaccuracy and inefficiency of the measurements. However, I don't think you counted efficiency correctly, since your charger doesn't go at 30 amps entire end of the charge, it likely drops at the last 15-20 minutes during CV phase, so actual inefficiency is less than you think.

Shunt based devices can be even less accurate, since they have to read 50mV range, probably need to amplify it before A/D conversion, which reduces precision even more. Try to read 2 Amp on your 500Amp ammeter.


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## JRP3 (Mar 7, 2008)

I never considered the possible effects of reduced resolution at low amperage. Dimitri, by using -10% compensation might I be under representing the amps out of the pack in my attempt to get more accuracy when charging?


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## jtgreeson (Aug 14, 2009)

> In reality, the end result is actually pretty damn accurate. I have collected ton of data during the design/testing to make sure the output is valid.


Thanks, Dimitri, for the detailed explanation and your previous hard work. 

Knowing that, I'm not going to touch a thing!


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## dimitri (May 16, 2008)

JRP3 said:


> I never considered the possible effects of reduced resolution at low amperage. Dimitri, by using -10% compensation might I be under representing the amps out of the pack in my attempt to get more accuracy when charging?


That is correct. By design, charging current shows 1-2 Amps more than actual. This is done to compensate for low resolution at low amps and inefficiency, to make sure display always gets to 100% full at the end of charge. This compensation is too small to be noticeable for regen, so I think you'd be better off without additional compensation. 

Most critical aspect of this device is correct zero point calibration. It must always show zero amps when the car is not running. It might take a few calibrations before you get it in the sweet spot, but once its there, it will work real well.


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## JRP3 (Mar 7, 2008)

That was part of the reason I used the negative current offset, I was getting current values when parked and would come back to a "full" pack overnight. -10% is probably more than I needed, I'll dial it back.


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## dimitri (May 16, 2008)

JRP3 said:


> That was part of the reason I used the negative current offset, I was getting current values when parked and would come back to a "full" pack overnight. -10% is probably more than I needed, I'll dial it back.


Sounds like you need better zero point calibration, rather than change in scaling. Note, its not an offset, its scaling, i.e. it does not change the zero point. Only calibration can adjust the zero point.

When you see the non-zero current with the car turned off, do a calibration right then and there, by holding both buttons for 5 sec.


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## JRP3 (Mar 7, 2008)

I did both at the same time and I guess it worked since I haven't had the problem in a while. I just attributed the fix to the current compensation.


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## honn1002 (Nov 26, 2008)

Just finished installing a voltage scale for the EV Display.


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## jtgreeson (Aug 14, 2009)

Honn, If you have time please give more details on your scaler. Thanks!


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## honn1002 (Nov 26, 2008)

jtgreeson said:


> Honn, If you have time please give more details on your scaler. Thanks!


 JT: The voltage scaler I’m using is 10:1. My battery pack has 44 cells. I’m charging at 3.5V per cell, so the full charging pack voltage is 154V. 15.4V is the max voltage goes to the EV Display which is slightly below the 16V rated filter capacitor on the sender board. My charging pack voltage is at the maximum for the 10:1 scaler. 

I used a small separate DC-DC converter to power the scaler and from the scaler output to the EVD. 

I got a small DC-DC from digikey. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=285-1885-ND


I got the scaler from Belktronix. http://www.belktronix.com/


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## jtgreeson (Aug 14, 2009)

Honn, Thanks for the details and the links. 

Are you using the "link10series e-meter HV adapter" from Belktronix or another one? I believe he lists 3 on his website. That small AC-DC converter from Digi-key is nice, it's listed as 264VAC max in and 15VDC out.

See if I understand: The AC-Dc output is 15vdc and you hook it to the 10-1 scaler which then is connected to the EV Display power in? Is the Belktronix scaler just a voltage divider (using resistors) or is it something else? Does the output of your scaler proportionally follow the voltage of the pack? Is there some way I could make a scaler to work on my 48 cell pack.? (I need a 12 to 1 reduction) Did I ask to many questions?


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## honn1002 (Nov 26, 2008)

JT,
The 10:1 scaler I’m using is not listed on the website. The AC-DC output is 15vdc + or – 2.8vdc. It can be adjusted between 12.2 to 17.8vdc max. I adjusted mine to 16vdc for the scaler to properly work. The AC-DC output is connected to the EVD power in.

This scaler is not just a voltage divider using resistors, it has more components. The output of the scaler proportionally follows the voltage of the pack as the circuit is designed for. 

The scaler only does 10:1. 48 cell pack might be slightly high. What is your full charged pack voltage?


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## david85 (Nov 12, 2007)

Silly question, but what is the diameter of the gauge?


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## dimitri (May 16, 2008)

david85 said:


> Silly question, but what is the diameter of the gauge?


Its a standard 2" gauge casing , designed to fit into 2" gauge pods.


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## jtgreeson (Aug 14, 2009)

More detail: in front of the 2" case is a 2 1/4 inch diameter bezel which is about 3/8 in deep. If you slide it into a 2" diameter cutout that bezel would stick out 3/8" and cover up the hole edge nicely. I have an extra case that I will not be using.


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## david85 (Nov 12, 2007)

I don't know how but somehow I got it stuck in my head that it was closer to 3". 

2" is perfect! JRP3 has been telling me to look at this for a little while and I feel an "I told ya so" coming on

So this can read amp draw and battery SOC simultaneously? 

And is there any problem powering it from the DC/DC converter?
I couldn't quite understand from the discussion if there are any issues with this.


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## JRP3 (Mar 7, 2008)

david85 said:


> 2" is perfect! JRP3 has been telling me to look at this for a little while and I feel an "I told ya so" coming on


 


> So this can read amp draw and battery SOC simultaneously?


Yup. You can configure both the upper and lower lines of display to show any of the parameters.


> And is there any problem powering it from the DC/DC converter?
> I couldn't quite understand from the discussion if there are any issues with this.


That's how I power it. You don't get pack voltage that way of course.


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## jtgreeson (Aug 14, 2009)

I also power it from my 12v aux. It works great. An added plus (if I understand it correctly) is that the pack Voltage "xxxV Pk" is really a multiple of your EV Display's power supply, in my case the 12v battery voltage. Knowing this I can monitor the status of the Aux Battery. I have 48 cells so I just divide the "pack voltage" by 12 and I get my actual 12v aux battery voltage.

If away from the car for a week or so I turn on my DC-DC to keep the 12v aux battery charged.

600 miles so far and the EV Display works super.


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## david85 (Nov 12, 2007)

I could run a separate volt meter for the pack voltage on the other side of the cluster. Volt meters generally don't cost that much and compared to other dedicated EV amp meters this isn't out of line. Besides, I have to put something on that side anyway since fuel and coolant temp are useless now

I was mainly wondering if running the DC/DC converter would affect accuracy at all.

So this does need to be powered at all times then. I can work with that.

Thanks guys, I think thats just about all I need to know.


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## david85 (Nov 12, 2007)

Sorry, one more question.

I'm wondering if its worth getting the voltage scaler. I'm reading through the manual and there is mention that its optional but it's not listed on the webstore nor is any price shown anywhere.

This should in theory give me a more accurate setup and eliminate possible balancing issues or the need to rig up a separate, always on ~12V power supply. Sounds like it would simplify the setup.


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## JRP3 (Mar 7, 2008)

Probably makes sense if you don't have an always on DC/DC or 12V battery.


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## dimitri (May 16, 2008)

david85 said:


> This should in theory give me a more accurate setup and eliminate possible balancing issues or the need to rig up a separate, always on ~12V power supply. Sounds like it would simplify the setup.


How is reading the pack voltage helping with balancing issues? You can't judge balancing based on a pack voltage, plus its not precise enough to show fractions of volts differences. 

Isn't there already a 12V battery in the car? What's there to rig up?

Voltage scaler is not really a simple setup, if it was, I would be offering it as I originally planned. What Honn has done is the only technically acceptable solution , but its difficult to offer as a packaged product since everyone has different voltage ranges and it needs a bulky DC-DC with appropriate input range.

As I said before, IMHO, its just not worth the trouble. But if you are skilled enough to rig up what Honn did, it should work well.


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## JRP3 (Mar 7, 2008)

I assume by balancing issues he means powering the display from 4 pack cells.


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## dimitri (May 16, 2008)

JRP3 said:


> I assume by balancing issues he means powering the display from 4 pack cells.


Doh, clearly I need more coffee this morning


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## david85 (Nov 12, 2007)

Ok, I understand now. When the term "optional" is used in a manual I assume it was something that can be purchased from the same vendor separately. Never mind then, I'll just get the display by iteself then.

I am not currently running a 12v battery, just strait power direct from the DC/DC converter and that isn't powered on normally so when I shut the car off, everything goes dead. I could probably rig up a small nickel battery since we have extra cells lying around.


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## JRP3 (Mar 7, 2008)

I'm having some odd behavior now that temps are dropping. Last night it got down to 40 for most of the night and this morning the display was showing a full pack even though I had 20 miles on it. So it's counting AHs when the car is off. Should I change the temperature compensation, the current compensation, or do another reset?


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## dimitri (May 16, 2008)

JRP3 said:


> I'm having some odd behavior now that temps are dropping. Last night it got down to 40 for most of the night and this morning the display was showing a full pack even though I had 20 miles on it. So it's counting AHs when the car is off. Should I change the temperature compensation, the current compensation, or do another reset?


Don't change any compensations, its not related, at least not based on what you describe. It sounds like it was counting Amps IN while the car was not charging, so the issue is with zero point calibration or poor cable connection , similar to what you had before.

When you looked at the display in the morning, was it showing non-zero Amps IN instead of zero amps OUT?

Another possibility is that display lost power during the night and got reset back to full pack when power got restored, which could also be due to poor cable connection.


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## JRP3 (Mar 7, 2008)

It wasn't showing any amps going in at rest this morning, just zero amps out. I suppose the cold could have made a weak connection worse, I'll have to take a close look at the individual contacts in the plugs as everything feels tight.


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## JRP3 (Mar 7, 2008)

Saw it showing 4 amps in on a 35 degree morning with everything off so I did a zero point reset, it's been fine ever since, down to 26F so far.


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