EV Power Consumption

Technical discussion on converting internal combustion to electric
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Simon
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Post by Simon » Mon, 12 Jan 2009, 19:04

Hi Magneto
Using battery voltage to estimate your depth of discharge is not very accurate but with sealed lead acid you cant use a hydrometer.
I also have Optimas in my car. The Optima website doesnt have any information on depth of discharge that I could find.
But here is a site that gives some data.
Getting the most out of your Optima Yellow tops
Does anyone else have voltage/dod tables for Optima YT?

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Post by antiscab » Mon, 12 Jan 2009, 19:20

the most accurate way i have ever come across to measure SOC is to use an AH counter, such as a xantrex link 10.

with a voltmeter, you can approximate your SOC, however the range of error is fairly large (+-20%).

Matt
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2017 Renault zoe - 25'000km
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Johny
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Post by Johny » Mon, 12 Jan 2009, 19:26

Great article Simon - good solid info. on the exact batteries Magneto is using. It looks like 50% for the Yellow tops would be 12.35 V per battery or 148.2 Volts. It would be very interesting for Magneto to tell us how many kilometers that gave you in range - the writer gets about 26Km.
Note that he lets the batteries sit for a couple of hours before checking their voltage - this is the problem with using open battery voltage for SOC estimation - it's way better that no estimate at all though.

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Post by Magneto » Mon, 12 Jan 2009, 20:08

Matt

I am using the Link 10 on the EV so I will have look at it and try and work out how to use to to estimate discharge from AH.

Should the AH metre be under load before taking a reading?

Thanks everyone for the great info. We need to design a EV 101 (as the americans say) for novices like me.

Regards

Magneto
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Post by antiscab » Mon, 12 Jan 2009, 20:45

the AH reading is a cumulative measurement of A drawn from the pack.
it makes no difference whether the pack is under load or not.

the AH meter should be reset to 0 after every full charge.
for the 55AH optimas, i think it was 30AH is the safe limit (i forget).
so at 30AH, you can consider your pack to be dead (even though it could probably still move the vehicle normally).

as far as setting it up, as long as it already setup to take A measurements on the battery side, it should already be counting AH.

Matt
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2017 Renault zoe - 25'000km
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1998 prius - needs Batt
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Post by Magneto » Mon, 12 Jan 2009, 20:59

Matt

You explain it better than the Link 10 instruction book.
Magneto Man

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Post by acmotor » Tue, 13 Jan 2009, 07:05

Just a comment on batteries as they age....

Ah metering (by say link 10) is one of the best methods of determining SOC, however it does require a good estimate of perkeut number, actual battery capacity and monitoring of temperature.
The perkeut numbers given in the link 10 handbook are approximations and can result in considerable errors on lead acid batteries as you approach even 80% DOD. (I have a link 10).
At 50% the SOC indication from link 10 is better.

What I am leading to is.... voltage droop (terminal voltage under load) is, I find, one of the best indications of SOC during deep discharge rather than no load voltage.
This is of course really needs to be read at each battery, however pack voltage is a good indication.

The other factor to look out for is the behaviour of the batteries as they age. Particularly if one battery has a problem.
% of Ah alone does not predict this, voltage must be considered as well.

The link 10 is good when everything is working fine.
iMiEV MY12     105,131km in pure Electric and loving it !

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Post by a4x4kiwi » Tue, 13 Jan 2009, 07:37

This gauge accounts for battery age and condition.
http://www.qsl.net/k5lxp/ev/evgauge/evgauge.html

I appears to to show the internal resistance of the pack.

quite simple and elegant. You might not want to have the whole pack voltage on the gauge, but you could sample 2 batteries.
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Post by Nevilleh » Thu, 15 Jan 2009, 22:53

Magneto, are your batteries "deep cycle" ? (I'm not familiar with the brand you quote). We use 12v x 50 AHr PbA deep cycle batteries in electric scooters and the specs for battery life are:
360 cycles at 80% DOD.
1000 cycles at 50% DOD.
So you can see you shorten their life considerably if you take them down to 80% DOD. Mind you, a scooter will go 60 kms to 80% DOD and about 33 kms to 50% DOD, so that's 21,600 kms compared to 33,000kms!
A fully charged 12v battery will show 13.2v after it has been disconnected from the charger for a short time. The voltage will drop to about 12.6v quite quickly under load and stay there until about 50% of it's capacity is used after which it will fall slowly and an 80% DOD is down to 10.5v. 50% DOD is about 11.0v. So you should monitor the voltage of your battery pack and if you work on those figures on a per battery basis, you will get about the best you can.
Note that the 50 AHr battery WON'T deliver 50 amps for an hour! If you suck 50 A out if it, you get about 25 minutes! It will deliver 2.5A for 20 hours though. (The beauty of a 40 AHr LiFePO4 cell is that it WILL deliver 40A for an hour!) So the slower you drive, the further you will go and if you use "gentle" acceleration so as no to suck 100's of amps - even for a short time - you will go even further.
Just as a comparison, I've ridden a scooter until the controller cuts out (10.5 v per battery) and then rested it for 10 minutes. It re-starts and will go a further 5 or 6 kms if you gently open the throttle and keep it down to about 25 kph.
A 12v charger puts out 14.4v when in "boost" mode and drops to about 13.6v when in "float" mode, so you can multiply those figures up to see what to expect from your charger.

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Post by Magneto » Thu, 15 Jan 2009, 23:15

Nevilleh

My batteries sound similar to yours. Mine are 12V 55 Ah batteries..

Thanks or all the good info.

Magneto.
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Post by antiscab » Fri, 16 Jan 2009, 07:53

Hi Nevilleh,

are those 12x 50AH, 6 cell batteries? or cells?
a scooter that takes 144v of 50AH must be a sight to see.
do you have a link?
have you actually achieved more than 10000km on any of your scooters?

on my scooter, my lead batteries never got past 4000km before failing (inititial range being 35km@80%).
my rides were all around 15km.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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Post by Nevilleh » Sat, 17 Jan 2009, 18:48

Hi Antiscab
No, they are standard 12v (6 cell) batteries, Yuasa "Portalac" made specially for electric scooters. We import into NZ the Taiwanese "EVT" scooters and have found them to be by far the best performers of the vast numbers of such machines being produced now. We keep well clear of Chinese made ones!
I've been running one of these for about 2 1/2 years, done 11,600 kms on it and the batteries which started out giving me about 60 kms down to 10.5 v are now giving about 50 kms to that voltage, so they are showing signs of wear and tear. I do a round trip of 46 kms when I use it for commuting and it copes with that quite easily. I charge it after every trip and usually leave it on overnight. It has need the brush dust cleaning out of the motor twice now and is due again and last time I did it I noticed the brushes were about 2/3 worn. Lot to be said for brushless motors! If they could only produce the same torque.
Anyway, if you were in NZ I could sell you one!
www.evtnewzealand.co.nz
We've sold heaps of these things and supplied new batteries to a few other people, but have had only a single customer whose batteries failed within a year. Probably because he crashed the thing and it was in the repair shop for 4 months with flat batteries. My experience of PbA indicates that you can completely stuff them in 4 weeks if you leave them completely discharged for that long.
I have a machine here with 16 TS LFP40's in it that we are testing and boy, do they transform the thing. I've re-programmed the micro to give full power at full throttle (normally they only do just over 50 kph) and it will do 70 kph when the batteries are first charged - it will travel about 80 kms on a charge if you keep it down to 55 kph and it is nicer to ride being 35 kg lighter.
My next project is going to be an electric car conversion!

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Post by antiscab » Sat, 17 Jan 2009, 20:18

hi Nevilleh,

brushless motors are actually considerably more torque and power dense than brushed ones (if you are prepared to push them to their limits).

i run the "1500w" motor in my emax at saturation up until 15kmh which gets a me a power plateu of 6000w from 15kmh to 45kmh.

your motor must have a lower volt/rpm coefficient than mine.
i need 19cells to achieve 70kmh (and in truth i would prefer to have 20).
i gotta say, speed really kills range. on my setup i get more like 40-50km range at 70kmh Image
i think after my car project, ill build a "real" motorbike with this hub motor:
http://endless-sphere.com/forums/viewto ... ffbf5c33f9

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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Post by antiscab » Wed, 21 Jan 2009, 05:47

acmotor wrote:
It would require the 3 phases to be at 120 degrees or it will get the power reading wrong. So connecting the inputs together to a single phase would not work. This is from basic theory, I must admit to never actually trying what seems unlikely ! If anyone has a spare 3 phase meter it would be interesting to put theory to test.


well Rob and I performed this experiment today.
i made the lives common on all three phases common, on both input and output, on this meter:
http://cgi.ebay.com.au/THREEPHASE-WATTM ... .m20.l1116

from circuit theory we know that the current flows each path proportionally to its conductance (1/resistance). so current was indeed flowing through each phase within the meter.

i then wired it inline with a standard single phase energy meter.

hooked this up to the charger for Robs BMW 318i (after I took it down Roe hwy a few times to knock some charge out of the batteries of course:p )

for the time period we ran the test, both meters read 1.1kwh consumed.

so, it seems making the phases common on this type of 3-phase energy meter doesnt affect its accuracy (at least not by enough to worry about).
id be interested to see how other models fair.
this meter is pretty cheap though.

Time for test #2.
how do people think it will react with a 240v DC input?

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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