# Cheap Ammeters and Voltmeters



## Mr. Sharkey (Jul 26, 2007)

KiwiEV said:


> Too good to be true or just a good bargain?


 Neither, just the miracle of modern manufacturing and cheap slave labor.

If the accuracy is good, pick up a few. The price of the ammeter is about what you'd pay for a precision shunt alone.

Be aware, though, that digital meter may look high tech, and give a to-the-tenth reading, but in a moving vehicle, they are much less than desirable than a "needle gauge".

Why?

Because your brain processes the two forms of information in different ways. Looking at a digital display requires you to recognize the numbers, translate them into a meaningful reading, then compare them to a known minimum/maximum/nominal value that you have to remember.

An analog meter can supply the same information by the relative position of the needle, which you can instantly recognize as in-or-out of the proper range without actually knowing the numeric value.

I have both digital and analog meter in my EV, and during on-road in-traffic driving I use the analog metering exclusively. A split-second glance at my volt and amp meters can convey all the information I need without having to even think about what the value is.

Also, digital metering values "jump around" a lot during the varying loads of an EV's operation, making them even harder to get a fast reading from.

For stationary troubleshooting and data logging, digital meters will always be more accurate, and therefore more useful when you don't have to time share with road hazards.


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## Coley (Jul 26, 2007)

I just bought the same 200 volt and 500 amp panel gauges from :
zeva.com.au

I have them mounted and ready to put in the car.
He also sent me a wiring diagram for them.

check with him @ [email protected]
about prices. etc.

Seems to me, that with the colored backlite, it would be no more dificult to glance at them than a digital clock with the unlit gray background.


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## KiwiEV (Jul 26, 2007)

Really? Are they "jumpy" or fairly fluid regarding their readings? I mean, do they update every microsecond or every second for example? I remember some of the old digital dashboards in the 80's updated every second or so. It was no fun to watch when accelerating.
Do you have a picture of how they look installed into your dash?


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## Mr. Sharkey (Jul 26, 2007)

Refresh rate has a lot to do with the amount of "jumpyness", but even fast refresh rates result in a display of numbers that are constantly in flux, making it hard to pin down the reading. Remember that a lot of this has to do with physco-recognition of values, which are more difficult to quatnitfy in a rapidly changing display.

Here's a piccy of my instruments. I usually leave the digital meter set for ampere-hours, which is a fairly slow progression, and is not a reading that can easily be displayed by an analog meter:









The digital display is set to DOD or % remaining remaining in this image.

As you say, digital speedometers are/were a come-down. When driving, you usually don't actually examine the numeric reading on your speedo, but have a built-in sense of about where the pointer should be for a given speed, allowing frequent glances to keep you in the right speed "zone". Doing voltage and current calculations in your head from ever-changing digital readings would away take a lot of the intuitive craft of of driving an EV in my opinion.


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## moldiebrownie (Aug 29, 2007)

I went with analog guages for the reasons Mr Sharkey stated..besides..they came in my kit anyway. This also allowed me to use this cool pillar mounted guage pod....heh heh...keeping it clean for the ladies!


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## KiwiEV (Jul 26, 2007)

I, um, just bought them both.

I couldn't resist it. I looked at all kinds of analogue gauges but these digital display ones just look so _cool!_ 
I guess I'm just a sucker for colours and flashing lights.


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## Coley (Jul 26, 2007)

Mine will be in the car after next week. No time right now to install them.
My shop is getting busy again....


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## KiwiEV (Jul 26, 2007)

moldiebrownie said:


> I went with analog guages for the reasons Mr Sharkey stated..besides..they came in my kit anyway. This also allowed me to use this cool pillar mounted guage pod....heh heh...keeping it clean for the ladies!


I absent mindedly stared at your picture of the pillar-mounted gauges until it clicked. I was wondering why on earth you'd put them there for your passenger to look at. You even mentioned it was fashionably there "for the ladies". 

I got it eventually, it's that whole different side of the car/road thing. 
I'm a little embarrassed right now...


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## Coley (Jul 26, 2007)

Well, I got mine in the car today and turned on the battery pack expecting to see 75-volts or so. 

The gauge read 36 volts and then nothing.

The amp gauge showed 1 amp and nothing more as I drove around town.

Tried to fire them up with the car battery first.

Changed to a seperate 9 volt battery, same results.

Not too happy at this time.

Voltmeter (handheld) shows 75 volts, right at the dash gauge so wiring should be OK.

9/16/07 Update

Today as I was driving back to town, the amp gauge reads "1000". No"dc a", just 1000.

9/20/07
Both meters are now blank, (with the nice blue background).

I have a new 12/12 converter coming from ZEVA and we will see if that makes a difference.

If not, I was told new meters would be sent.


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## KiwiEV (Jul 26, 2007)

Hmmm. That's bad.

Did they definitely give you the 12v input version or maybe they cocked up and sent you the 5 volt input version?

That's got me worried now. If mine do the same then I'll have to drop that idea and go with the needle gauges that others use. Would be a terrible waste of money if they don't work.
Not sure about the voltmeter but you could try wiring from the shunt to your handheld ammeter, going for a drive and seeing if it's the cheap chinese shunt or the actual gauge that's faulty.
I hope you figure a way to let you use them ok. Let us all know if they work ok (especially me!)


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## Coley (Jul 26, 2007)

I didn't see a 5volt set, but these can either be a 9volt or the car 12volt for feed.

I should be getting the new 12/12 converter soon. 

Both meters were blank today, except for the nice blue background.....

just plugged it in, for the trip to work tomorrow.


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## KiwiEV (Jul 26, 2007)

Hey Coley, my meters arrived today and they have some odd warnings which I didn't expect.
Out of interest, did your meter come with this note:
WARNING:
The voltage meter and the current meter can not jointly use one DC power supply.
If you are unable to supply the single working power, please buy our DC-DC converter Isolated Power Supply.

Well. That's just what I need. After buying something being told that I need something else to make it work.
Is that the reason yours failed?

"There you are sir, enjoy your new Audi"
"Thanks! Ummm... Where are the keys?"
"Oh, you want to USE your car? I'm very sorry sir, keys cost extra"


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## Coley (Jul 26, 2007)

Mine didn't state that, but it may be why they failed.

I am getting a new 12/12 converter (free), because the original one was marked with reverse polarity.

THAT may have been the thing that did my meters in.

I am going to hook them up to a 9volt battery and check them, to see if they will work that way.

If that 12/12 thing is true, then you would need 2 of them, (one for each meter).

Not fun....


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## KiwiEV (Jul 26, 2007)

I've just bought one 12v/12v isolator off that same guy in China that I bought the meters from. 

Surely I'd only have to use one isolator for one meter, as the other meter would be effectively on a "different" feed. Anyone?

I hope so as I don't really want to spend another $20 getting _another_ isolator sent down here.


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## Greenflight (Sep 13, 2007)

IDK, sounds like the Chinese may have lost it... This makes no sense. Why would they require two separate supplies? I mean, the 12v should just power the display and such- not take the actual reading, right? Or is there something I don't understand (please no remarks about the meaning of life  )?


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## Mike D EV (Sep 11, 2007)

Many cheap digital panel meters do not have isolated inputs, and internally reference the signals to the supply ground. 
Depending on where in the circuit you place the amp shunt, that could blow one or both meters. 

KiwiEV's included warning note would be appropriate for that type of meter.

Coley's idea of testing them with 9V battery would be a good way to test them . 
I have also seen DPM's that are rated for 12V, that would be damaged at 13.6V, so check the max volts spec.
From the description, only the ammeter should need an isolated dc/dc.
Good luck.


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## KiwiEV (Jul 26, 2007)

Thanks mate, I'll give it a shot with the 12v/12v isolator on the ammeter.
You mentioned that the location of the shunt within the circuit could cause the ammeter to get a little upset... Or die. 
Or both.
Presuming my ammeter is a die-before-you-buy model, where would you recommend placing the shunt?


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## Mike D EV (Sep 11, 2007)

If your complete 12V system is powered from an isolated dc/dc converter, that is not common with your HV battery supply, and your volt meter is powered with that supply, and your ammeter is powered with the other isolated dc/dc, the placement of the shunt in the circuit should not matter.
My reference to the shunt location was without isolation.
A simple ohmmeter test or visual circuit trace of the meter circuit should tell us if the measuring input terminals are common with the power inputs.
Need the specs or better yet a schematic of the meter to make an assumption free determination.


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## KiwiEV (Jul 26, 2007)

I'm not going to use a DC to DC converter in my EV. Too hard, expensive etc.
The car's 12v electrics are powered off an AGM battery tucked away in the engine bay. Not sure if that affects the shunt location.


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## moldiebrownie (Aug 29, 2007)

KiwiEV said:


> I'm not going to use a DC to DC converter in my EV. Too hard, expensive etc.
> The car's 12v electrics are powered off an AGM battery tucked away in the engine bay. Not sure if that affects the shunt location.


 
Kiwi, I started out like that, (no dc/dc converter) and it gets old real fast charging up the aux battery all the time.


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## KiwiEV (Jul 26, 2007)

It's no problem for me as I already have the "accessories" battery connected through the multi-pin socket to a battery charger. It gets charged at the same time as the other 12 batts when the car's plugged in.


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## Greenflight (Sep 13, 2007)

Yeah, I'm not running a dc/dc either. I have a $25 wal-mart charger hard wired into the system. It's not too bad.


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## Coley (Jul 26, 2007)

I tried to send you a copy of the wiring diagram that I have for my meters from ZEVA but the email failed 39 attempts to get to you.

It shows both meters being fed by One-12/12 unit.


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## KiwiEV (Jul 26, 2007)

That's odd. It could be my spam catcher on my email. It's fairly strict and I can't adjust it or I'll end up with 200 spam emails a day.
You're sending it to [email protected]? 
Try writing my name or something in the text field, it might help the spam catcher realise it's a personal email.

I fired up my voltmeter this afternoon. It works well so far. I supplied a seperate feed (off a battery charger) and got 16 volts on the display! So that's working anyhow. My 12v/12v converter should be here in a fortnight and I'll wire that up to the ammeter. I haven't tried connecting that yet until I can give it an isolated feed.

Far out, I'm running out of little things to do as I need the racks installed before I can start the big jobs. Found some rust to keep me busy though...
I got a mention in the local paper today as well. Check it out here!


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## KiwiEV (Jul 26, 2007)

Wow! I'm a senior member now!

Senior eh?
Suddenly I feel as though I need a new hip joint.


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## Mr. Sharkey (Jul 26, 2007)

KiwiEV said:


> Suddenly I feel as though I need a new hip joint.


No, that's what happens when you reach 200 posts. All that you can expect now is that you will become forgetful and your hair will start turning gray and falling out...


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## Coley (Jul 26, 2007)

The shunt should have no bearing on the meter reading.

Mine is on the - side of the battery pack as requested.

I am redoing my meter panel today to make room for a push on/off switch. 

Should have it wired to the new 12/12 just for a test, but I think both meters are dead.


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## Coley (Jul 26, 2007)

I got the new 12/12 converter and still nothing on the meters.
Am getting a new pair, as the first 12/12 must have done them in. 

Gav.

A friend showed me his new set of the same gauges and his work fine.

He feeds them with a 9 volt battery, so they are independant of any of the car batteries.

He feeds them both with just one battery. 

The readings refresh about every 20 seconds and are very easy to glance at them and see the readings.

Not jumpy at all.

Now if I can just get mine going.


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## KiwiEV (Jul 26, 2007)

Once every 20 seconds? Yikes. By the time I figure out how many amps I'm using from a standstill I'll be at cruising speed!

My voltmeter (same as yours) responds much faster than once every 20 seconds. I wonder about the ammeter though...
I still haven't got my ammeter going as I don't have my 12/12 isolator yet (should be here this week) but I might try it with a couple of batteries and the motor and see if I get a reading.


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## Coley (Jul 26, 2007)

OOPS Senior moment!!!!

I should have said about 1/20 of a second. 

We were talking a lot while riding around.

It should be as fast as your voltmeter.

Seemed nice to me.

10/12/07
The meters came in or at least the voltmeter did. the bag was torn up and the 12/12 plus the amp meter were lost.

I put the volt meter in and I like it!
My charger is putting out more than I thought.
After a charge cycle, the meter shows 84 to 87 volts.
A trip home from the shop shows no pulldown below 60 volts, even while driving the last hill.
When I get there the pack still shows 72.5 volts.
No problem glancing at them while driving.

Now if I can get the amp meter.....


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## Coley (Jul 26, 2007)

I got the amp meter and put it in.

I am drawing 50 amps or so on level ground @ 30 mph.

The most it pulls on the largest hill is 169 amps.

After you run on a while with the 9 volt battery, the voltage will drop a bit and the gauges will show erratic readings.

I just turn mine on now at the start of a drive, as I cover the same ground twice a day.

I like the way they look and work.


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## KiwiEV (Jul 26, 2007)

Hey Coley, what kind of car do you have and what voltage is it running?
Just curious. 
Good to see you got your meters running. I'm still waiting for the last rack to go in. Hopefully my welding guy will show up today.


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## Coley (Jul 26, 2007)

My car is the Yugo in the EValbum.

Running 72 volts.


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## dbgtwill1 (Dec 11, 2007)

another reason analog might be safety can tell sooner dont have to look as long can watch the road more
but thats my Opinion and there like but holes every1 got 1 some stink more than other 
luck 2 you
\dbgtwill1


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## KiwiEV (Jul 26, 2007)

I'd forgot about this thread.
Now that I have the meters in and working, I'd have to say in all honesty I'm glad I bought them instead of the analogue gauges. They're accurate, refresh really fast, and most of all look really modern in any dash. I'd recommend those digital ones to anyone. 
Now that I have them, I love them! Choosing analogue or digital meters just comes down to a matter of personal choice I guess.


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## Coley (Jul 26, 2007)

Mine are off to the right of center on my dash and very easy to just glance at.
They are easy to view at night also.
I really like them and very glad I bought them also...


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## dataman19 (Oct 7, 2009)

OK..
I have been reading this post and have a comment about isolated inputs...
..
Does not a blocking diode provide isolation.. or has the physics changed for EVs?
..
When you have two DC Loads using the same DC Source you use one diode (preferably two - one fore each load) in line to provide isolation. The diode keeps the two loads from interacting with each other.
..
This applies an effective isolation. But the total load will be the two loads added together (you cannot use isolation to drive two 1 amp loads from a single 1 amp power source - they are isolated, not separate).
..
Just my 1.34 cents worth.
..
Dataman19


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## Mike D EV (Sep 11, 2007)

An isolated meter uses a dc/dc converter on the power supply side so that you can connect the inputs to any voltage without any current flowing into the power supply.
Kind of like a hand held meter running on batteries.

An example would be to measure a battery in a series string even though it may be the last one in the string and could be at 100 or more volts respective to ground.

A non isolated meter will usually have the negative input connect to the negative power supply lead of the meter, so there is no way you could measure voltages outside of the meters power supply range.

I have a 9v battery powered DVM in my car,which can measure any of my 4 12V series batteries, the full 48V booster pack, my 144V hybrid pack, battery temperature and current, but instead of running off batteries, I use a 12V to 9V isolated dc/dc converter which floats the meter so it works just like it would if battery powered.
The converter cost about $7,The input to the DVM is selected with a 12 position rotary switch.


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## cruisin (Jun 3, 2009)

I would be very careful using the cheap Chinese Volt and Amp meters off ebay and elsewhere as they ALL have a common ground to to measuring voltage. This means that the groung for your traction power will be grounded to your car. VERY BAD. The way I did it was to use small low power consuming DC converters to provide 120v to 12v for the meters and to charge the 12v battery at all times. The DC converters are isolated and provide about 5 amps which is more than enough. Also, the meter is on at all times so you may check the voltage without having to get in the car. The DC converters cost me about $25 each, are solid state and very small. My 2 cents worth, because I learned the hard way and almost got wacked for good. my email is [email protected]


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## JRP3 (Mar 7, 2008)

What converters did you use?


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## cruisin (Jun 3, 2009)

JRP3 said:


> What converters did you use?


VICOR or similar models


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## JRP3 (Mar 7, 2008)

Do you have any sources for 120 volt Vicors?


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## Coley (Jul 26, 2007)

I have been running my meters from a single 9volt battery for 16 months.

Works great and no problems.

Would do it again.....


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## Amberwolf (May 29, 2009)

For those that need to run these meters off your packs but don't have a DC/DC converter to do it with, you might look into the little celphone AC adapters. I've been testing the many I have around here, and almost all of them will run from DC, usually as low as 48V and sometimes as low as 24V. 

Some require a specific polarity, but if you bypass the bridge (as recommended) then you'd have to be polarity-careful anyway. Most don't care, but if you're running thru the bridge rectifiers to prevent having to open up the little case, remember that you are only using half the rectifier to get power into the device, so it may only be safe to use at somewhat less than it's rated output. 

If all you need is 500mA to 1A at 3V to 9V, you can probably find a celphone or PDA (or other device) wall charger that is a switching type, and probably for free from something you already own but don't use anymore. If not, Freecycle.org and Craigslist, or your local thrift stores and garage sales. 


Pretty soon I'm going to start a collection and test service for this sort of thing, so I can determine what the chargers will run at for DC, and provide output-wise, then mail them out to people that need them. Cost is yet to be determined, as it will depend on actual average charger costs, but I can't imagine it'd be more than a few bucks plus postage in a padded envelope or very small box (they're really light).
________
FIND HEADSHOP


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## Stunt Driver (May 14, 2009)

Just be carefull with those cell-phone chargers, as they don't isolate power. And if you run LCD voltmeter from non-isolated power - it will blow. You'd think that aux 12v batt is isolated, but not really motor case is aux negative, and there is always a small leak from armature to case.

Done that. Blew one.

Bought my scales from the same ASIA Engineer seller. http://www.diyelectriccar.com/forums/showpost.php?p=142186&postcount=78
But some meters are cheaper at other sellers ($6 for mini 100v meter) - just keep looking at ebay.
Bought isolated dual output power supply for $15 from asia engineer as well.


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## Amberwolf (May 29, 2009)

Some of the ones I've tested appear isolated (no continuity from AC to DC connections), some not. I've yet to open them up and verify their designs.
________
Erica_Lopez


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## bipole (Sep 8, 2009)

Are the LED and LCD meters from Asia Engineer dimmable? Concerned about being too bright at night.

Thanks


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## Coley (Jul 26, 2007)

I don't know about that, but I have mine on their own switch and when I drive at night, I shut them off.

I drive the same route 4 times a day and pretty well know what the readings are by how the car drives.

A quick check before starting out and then shut them off.

They are on the right of center of my dash and really don't bother that much.


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## cruisin (Jun 3, 2009)

Here is what I did and works well. I use a modified Vicor DC converter ($30 from [email protected]) connected to half of the traction power (48 - 75v) to charge the auxillary battery all the time at 100watts 9amps and a second Vicor on the other half of the traction power to power a LCD Volt meter that has a button to turn off the back light. No light during the day and light at night. Because these cheap digital meters are NOT isolated, it is very important that the meters have their own isolated power source or else you will blow them up as I did many times trying to work around the problem. Also, some controllers i.e. KELLY have a circuit connection between traction power negative and the 12v ground of about 3 amps. This leads to other potential problems. RULE OF THUMB IS NO COMMON GROUND BETWEEN TRACTION AND CAR BODY. With a continues charge on the aux battery, it mantains about 12v with very little drain on the tyraction batteries. Same for the Vicor feeding the Volt meter. The Vicor could also be used to power other 12v items with a rating of 9amps output. I believe this design provides a lot of safety and is extremly dependable, unlike the higher powered DC converters sme people are using. My 2 cents.


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## bipole (Sep 8, 2009)

Coley said:


> I don't know about that, but I have mine on their own switch and when I drive at night, I shut them off.
> 
> I drive the same route 4 times a day and pretty well know what the readings are by how the car drives.
> 
> ...


Thanks Greg, that helps.


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## chansen (Mar 13, 2009)

I also use the chinese volt and amp meters. I originally had a problem with noise maybe from the curtis controller and/or motor. It caused the meters to display erratically every now and then.

Added a DC-DC converter (as cruisin suggested) that not only provided the isolation from the chassis 12volt circuit but also got rid of most of the noise. I did add small coil shunt and de-coupling cap on the DC-DC 12V output supply lines to the meters just in case.


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## Stunt Driver (May 14, 2009)

bipole said:


> Are the LED and LCD meters from Asia Engineer dimmable? Concerned about being too bright at night.
> 
> Thanks


 
ones I got from Asia Eng are not dimmable, but i wouldn't say they are too brignt - I drive regularly at night, and don't see any discomfort. Just the right brightness imho.


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## bipole (Sep 8, 2009)

Stunt Driver said:


> ones I got from Asia Eng are not dimmable, but i wouldn't say they are too brignt - I drive regularly at night, and don't see any discomfort. Just the right brightness imho.


Thanks, are you using the LCD or LED? What color?

I just ordered two red LED ones, 5-15v and 0-500v. Just can't beat the price, less than $20 shipped. I just was in TAP Plastics and they gave me a 1/8" x 6" x 18" smoked polycarbonate sheet they had as scrap, i was thinking if it is too bright, I could attach a panel over them.

Thanks.


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## bipole (Sep 8, 2009)

Mr. Driver, never-mind on the type, i just checked out your garage- blue LCD's. Nice work on the dash panel, I like it!


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## Stunt Driver (May 14, 2009)

I'm back to gauges myself. Built a small panel with 3 min-volt meters to watch my 3 not so well feeling batteries.

Seller sweared they do not require isolated power. ANd they can work of the measured battery. BUT

when I connected 12v power from AUX battery, and tried to measure one of my pack batteries - thin ground wires smoked up. 
I was too foolish not to check continuity. And ofcourse ground for power and measured V - are connected. 

How is your dash doing, Bipole?


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## Stunt Driver (May 14, 2009)

Looking at my issue - looks like there are two separate problems:

1 - Power must be isolated from pack, so input cap won't blow up on the voltmeter
2 - Grounds of voltmeters must NOT be conencted, to avoid short circuiting batts.


I can solve first one by buying isolated power supply module at $10 from ebay, but I definitely don't want to buy 3 of them.
So for #2 - looks like diodes on ground lead to voltmeters should help, so current can't pass from one gauge to another.


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## Jimdear2 (Oct 12, 2008)

Stunt Driver said:


> Looking at my issue - looks like there are two separate problems:
> 
> 1 - Power must be isolated from pack, so input cap won't blow up on the voltmeter
> 2 - Grounds of voltmeters must NOT be conencted, to avoid short circuiting batts.
> ...


After smoking a couple of the Chinese amp and volt meters, I also found out about the isolated power supply. 

I also found out that most of these resellers DO NOT have any knowledge of how this stuff works. They usually have to go back to the engineer in China and then they still get the info wrong. 

A couple of others on the site have run into this and posted the information about how they solved it. 

Probably the most inexpensive way I have seen to power the guages is use a 9 volt battery for each gauge (make sure the guage you order will work with that as power). I believe one fellow on the site said he just left the gauge powered and snapped in a new battert every couple of months. I suppose you can figure a more elegant way to isolate the power, but for simplicity sake, a $2.00 battery and a $0.25 battery harness is right in there.


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## Stunt Driver (May 14, 2009)

I have 3 of them, so buying isolates power supply will pay back in 2 months, and much more elegant, Just not sure about diodes.

And you are right, i guess, they only knows it works if you got one battery and one meter, but have no idea on details. Well, considering the price - i wouldn't ither.


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## Coley (Jul 26, 2007)

Mine are still working great.

Would buy them again..........8500 miles


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## Stunt Driver (May 14, 2009)

Surprise-surprise, voltmeters don't age!

just need to get them working in the first place. Just having a battery to replace is a bit weired.

By the way, Coley, how do you turn meter off?


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## cruisin (Jun 3, 2009)

I KEEP WARNING EVERYBODY THAT YOU MUST USE A ISOLATED CIRCUIT with these digital guages.


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## Stunt Driver (May 14, 2009)

100% agree.

I have just ordered one from ebay, because weired things happen - if I plug my pack of voltmeters to battery pack, even with diodes in the negative aux 12v to each voltmeter - still get a short thru negative power lead on most right voltmeter! Which doesn't make much sense to me yet. Looks like tracktion pack has more or less good contact with aux thru motor (which is not new, and it is very wet now in OR)
When I turn ignition off - middle voltmeter is not powering down! (most right is disconnected now).

I'm sure none of this will happen with isolated power supply


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## Coley (Jul 26, 2007)

Stunt Driver said:


> By the way, Coley, how do you turn meter off?


I have them on a seperate pushbutton switch that turns them on when I need to take a look.

I bought an extra set, of these gauges, thinking I might need them, but these are working fine. Just need to put a nine volt battery in, every so often.


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## Lordwacky (Jan 28, 2009)

This is what I bought to do the job for isolated power for my meters. I figured that at 2watt rating I can power multiple meters off the same circuit. That may or may not be defeating the purpose though.


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## Jimdear2 (Oct 12, 2008)

Lordwacky said:


> This is what I bought to do the job for isolated power for my meters. I figured that at 2watt rating I can power multiple meters off the same circuit. That may or may not be defeating the purpose though.


Lordwacky,

I've used similar unit fom the same supplier. 

I power one meter from the aux battery switched power and one meter from the isolated power supply. If you add a third guage you will need another isolated power supply. (don't ask me how I know).

All of these cheap Chinese electronic meters MUST be completly isolated from each other.

Hope this helps.


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## Stunt Driver (May 14, 2009)

Jimdear, I think diodes are enough to prevent common ground between meters, and no need to have them isolated. That is true if meter has common ground for power and signal, like on my picture above.

I have added diodes and they work.

Isolation from tracktion pack is needed to separate voltages, not currents, At this this is true for my setup.


($$ saver)
I was too quick to order isolater power supply, like on picture above, for $10 from ebay. BEsides, it is only 1W, and my meters seems to be drawing 0.5w, so i can't power 3 of them from single unit.


INSTEAD looks like I can use any AC cell phone power adapter! Just tried one from sony-erisccon - it perfectly works from 48V DC and higher! And gives around 5W. I'm sure all of us have a few unused power supplies left from died phones. If no functional difference - why pay more?


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## Stunt Driver (May 14, 2009)

Ok, story not over.

Even with isolated power supply (laptop PSU running off 48V DC) - still have problems - voltage positive measured lug travels thru next voltmeter ground to AUX ground, from where thru power supply travels to positive AUX and back to next voltmeter - becoming +12v on power leads. +24 on next voltmeter, and there it goes up. Mine didn't blow up because I only had 3, and they handle 24v power ok.

So seller suggested me to add diodes on negative measured leads, and recalibrate voltmeters. I didn't like this, but can't find other option. Will try this now. But at least one isolated power supply needed even here.

Or still other safe option was to use independent isolated power supplies for each voltmeter (which is $10 on top of $6 for voltmeter itself)


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## Coley (Jul 26, 2007)

Mine are wired to ONE 9 volt battery and there has not been a problem.

Same voltage input on each hooked together and the same negative with the outputs.

I should have said, both plus and minus for each gauge, goes to the 9 volt battery.

The supplied dc/dc never worked right for me.

Not sure what is happening to others.....


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## Stunt Driver (May 14, 2009)

your 9v battery is called isolated power supply

How many voltmeters you have? Are they hooked up to different batteries within single link?
If yes - then your voltmeters DO NOT have common ground for power and signal.


Also, copy link to your voltmeters - would be handy to know tested seller, and not having common ground is very handy.


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## Roy Von Rogers (Mar 21, 2009)

KiwiEV said:


> I absent mindedly stared at your picture of the pillar-mounted gauges until it clicked. I was wondering why on earth you'd put them there for your passenger to look at. You even mentioned it was fashionably there "for the ladies".
> 
> I got it eventually, it's that whole different side of the car/road thing.
> I'm a little embarrassed right now...


Dont feel bad, its what happens when you drive on the wrong side of the road..lol

Reminds me the first time I drove a Sunny Datsun in the UK, everytime I had to make a turn and wanted to click the turn signal on, I was using the wrong lever and the windshield wiper and washer came on...by the time I arived at the house, I had a very clean windshield..lol

I had a tough time getting used to driving on the other side, at times it was comical.

Roy


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## Stunt Driver (May 14, 2009)

Ok, I'm done. My cheap meters need:
1 - isolater power source OR in other words - zero voltage between signal ground and power ground.
2 - isolated grounds between meters in one stack (otherwise negative sides of all batteries in link will connect thru meters)


I have put a 12v relay on ignition 12v, which connects each voltmeter to it's battery for both power and measurement. Measurements seem correct.

Some meters on ebay don't have issue #2, but it's hard to tell before you buy them.


ps. meters show 1 MAXX29 (most right) and 2 old starting batts obtained for testing. Clearly, old starting batts don't hold for as long as MAXX29 does. Will be buying more MAXX29 now, but will keep watching individual voltages. This is my manual BMS, to avoid overdischarging of weak batts. Not scalable for LiPo cells, but good for budget conversions. Will go for 3 more meters soon


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## Coley (Jul 26, 2007)

I have a volt and an ampmeter for my pack. 

Both are run off one 9 volt battery. 

Yep isolated from the car and pack, but not each other.

I don't have the link anymore, as I bought them over 4 years ago.,..

The newer digital meter that checks just one battery is one of the cheap ones on ebay.
Here it is:
http://cgi.ebay.com/NEW-DIGITAL-7-F...emQQptZLH_DefaultDomain_0?hash=item3ca9ca8a6f

I have another one of these that I check each battery with also, just to check levels.

I have the one on the battery,in the pack stuck on with double face tape.


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## KiwiEV (Jul 26, 2007)

Roy Von Rogers said:


> Dont feel bad, its what happens when you drive on the wrong side of the road..lol
> 
> Reminds me the first time I drove a Sunny Datsun in the UK, everytime I had to make a turn and wanted to click the turn signal on, I was using the wrong lever and the windshield wiper and washer came on...by the time I arived at the house, I had a very clean windshield..lol
> 
> ...


It's funny you should say that! This was me attempting to drive on the "foreign" side of the road when I was in Europe.






Yup, that's the sound of me panicking near the end.


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## Stunt Driver (May 14, 2009)

Coley said:


> I have a volt and an ampmeter for my pack.
> 
> 
> Here it is:
> http://cgi.ebay.com/NEW-DIGITAL-7-F...emQQptZLH_DefaultDomain_0?hash=item3ca9ca8a6f


Coley, you have posted your concept quite a few times within this single thread now, thank you again. Any pics of installation by the way? 

About china made multimeter. While that thing is fully isolated - that is not what I would use in EV conversion because of it's uglyness and size. 

Your meters require isolated power. Also, you installed them luckly to have ground of Amp meter and ground of Volt meter - going to the same point of tracktion battery. Now, if you will reverse your volt meter signal wires - all will blow up in smoke. Not sure if you knew this or just got luckly installing. Look up my posts with wiring to understand current flow.

The reason why you fried you first set of blue LCD meters - you didn't have isolated ground. While we all believe we keep tracktion pack isolated from AUX battery - it is not true, and leaks exist thru motor. My tracktion + appears leaking to chassis, that means if I measure voltage between tracktion pack (-) and aux battery (+) - I will get tracktion voltage+aux voltage.


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## Coley (Jul 26, 2007)

I fried the first pair because of the wrong wiring diagram sent by the seller.
No problem since.

The muiltimeter is under the hood, fastened to a battery. Not ugly at all and keeps an eye on the charge rate.


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## green caveman (Oct 2, 2009)

A number of eBay vendors seem to have Blue LCD Voltmeters with a range of 7.5V-20V for about $5-$6. No external power supply is needed. I'm thinking of buying a dozen or so of these for monitoring each (8V) battery in the pack. It's a used pack (I figure you're going to trash the first one, might as well not be too expensive) so I'm really trying to monitor imbalance, I think that these should be close enough

Since these are backlit, I think that it would be a good idea to have the ability to turn them off. My thought is to simply add a transistor to all the meters and pull it in with the 12V DC-DC, with a switch in that circuit in case the bank of meters gets annoying.

That last sentence represents about the extent of my knowledge of electronics, so if anyone has any suggestions, advice, etc. I'd appreciate it. Is there any problem with pulling the base of all the transistors to the same 12V supply (isolation?). Anything else I should consider? Is there any particular transistor family that has a very low voltage drop (and isolation)? Anyone have particular parts to recommend/stay away from?


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## illuminateddan (Dec 19, 2009)

Hi,

The idea would work, but a quick word of warning: Having a meter per battery is fine as each meter would have it's own reference ground on it's own battery. If you the connect in a transistor switch you would need to make common grounds across batteries which equals short circuits across batteries!

Take the first battery in a series pack, it's voltage is 'x' between -ive and +ive. if you then measure from your first batteries -ive to your second batteries -ive you will find that because the batteries are in series you would effectively be crossing across the +ive and -ive terminals of the first battery.
Thus the voltage at each ground on each battery becomes x,2x,3x,4x and so on.

Keep each monitor isolated. if you really want to use a transistor on each then use an optocoupler to physically separate the transistors from your switch.

Hope this helps???


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## green caveman (Oct 2, 2009)

illuminateddan said:


> Hi,
> 
> The idea would work, but a quick word of warning: Having a meter per battery is fine as each meter would have it's own reference ground on it's own battery. If you the connect in a transistor switch you would need to make common grounds across batteries which equals short circuits across batteries!
> 
> ...


Am I correct in thinking that I could just us an optoisolator as the switch? Is there a problem with voltage drop or similar? It also seems that there might be some adjustment on the meters that might let me compensate for the voltage drop.


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## illuminateddan (Dec 19, 2009)

an optoisolator is an LED and a phototransistor in a single package, they are designed for signal isolation and so the phototransistor would not be suitable for a switch, however, you could easily connect the output of the optocouplers phototransistor to a larger transistor which could take the current. the led's in the optocouplers would then be linked in parallel with suitable resistors (V=IR so at 12v with a LED voltage of 2v and avarage current of 20mA you would need a (R=(12v-2v)/20mA = 500 Ohms).
Also be aware that many of the cheapy meters are not easily adjustable, so do the research with a test unit first!


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## gdirwin (Apr 7, 2009)

Your discussion on meters and switches got me thinking - if I have 2 current shunts (one at the battery and one for the motor) and 1 analog meter (0-1000A), can I use a DP switch to switch from one to another?

I would be worried about the potential difference between the 2 locations - even though it is only 100mV for each shunt, the potential difference between them could be the full pack voltage! If the switch goes through a neutral position first (so there is no commutation between one set and the other) and the switch is rated for 200V, it might work...

Has this ever been done?


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## green caveman (Oct 2, 2009)

gdirwin said:


> Your discussion on meters and switches got me thinking - if I have 2 current shunts (one at the battery and one for the motor) and 1 analog meter (0-1000A), can I use a DP switch to switch from one to another?


Not quite what you asked, but..

I have two 800A shunts, which I got for next to nothing, but I haven't started looking for meters for them yet. I was thinking of adding an instrumentation amp and then using one of the low cost meters. Precision would be about 1A (with the decimal point in the wrong place 1.00V = 100A), accuracy would probably be worse since I'd expect some noise on the lines, but I doubt that more is required. The lowest cost meters are 7.5V-20V so that wouldn't work, but 0-20V are readily available and only a little more.

If this would work, then you could add another meter for not much more than the cost of a switch.


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## major (Apr 4, 2008)

gdirwin said:


> Your discussion on meters and switches got me thinking - if I have 2 current shunts (one at the battery and one for the motor) and 1 analog meter (0-1000A), can I use a DP switch to switch from one to another?
> 
> I would be worried about the potential difference between the 2 locations - even though it is only 100mV for each shunt, the potential difference between them could be the full pack voltage! If the switch goes through a neutral position first (so there is no commutation between one set and the other) and the switch is rated for 200V, it might work...


Hi gdir,

Sounds like it will work to me. Typically the current shunt is wired directly to the meter. Putting a switch in the sense line may add a slight voltage drop and affect the reading, but not likely by much.

You bring up an interesting point about the potential difference between the two shunts and the switch contacts. When using a PWM controller, it will either be a high side or low side switcher. So, you will have one motor lead and one battery lead that are always at essentially the same potential. If you look at the Curtis series motor connection diagrams, you will note that the battery positive connects to the controller terminal B+ and also to the motor terminal A1. So it is a low side switcher. And then if you put the battery shunt in the line from battery positive to controller B+ and the motor shunt in the line from controller B+ to motor A1, then the two shunts will only have millivolts between them.

Regards,

major

[h2]Curtis 1231C Wiring Diagram[/h2]
*








*


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## illuminateddan (Dec 19, 2009)

gdirwin said:


> I would be worried about the potential difference between the 2 locations - even though it is only 100mV for each shunt, the potential difference between them could be the full pack voltage! If the switch goes through a neutral position first (so there is no commutation between one set and the other) and the switch is rated for 200V, it might work...
> 
> Has this ever been done?


This would definitely work although I would probably use a DPDT relay rather than a direct switch. This way you are switching the complete circuit (both legs) and do not have to have any HV coming to your dashboard.

Also, in the unlikely event of something going pop, it's well away from the driver!!


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## major (Apr 4, 2008)

illuminateddan said:


> This would definitely work although I would probably use a DPDT relay rather than a direct switch. This way you are switching the complete circuit (both legs) and do not have to have any HV coming to your dashboard.


Hi illum,

I fail to see much difference. You're going to have the ammeter on the dash, right? There is going to be little difference in potential difference between the meter wires and switch wires. Yes, they are "hot", meaning connected directly to the traction pack. So treat them as such. But the potential difference between the wires is so low that a short between them would not cause an issue. Your meter wouldn't work properly, but the shunt would conduct, not the lead wires. The possibility of a ground seems no more likely with the switch on the dash as just the meter.

But no harm if you want to use a relay. Just unnecessary in my mind.

Regards,

major


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## green caveman (Oct 2, 2009)

There's a discussion in this thread suggesting that you should fuse both legs of the wiring to the ammeter at the shunt(s).

"Ammeters almost never short. however, the wiring from the shunt to the ammeter as well as the wiring to the voltmeter connect directly to the pack which is over 120 v. when charged and usually over 1,000 amperes of current for at least a minute or more when those little wires and their plastic insulation short out somewhere along their route especially as they pass thru a hole in a box or the firewall, and such. That is why there should be a protective fuse next to the pack or shunt terminal where you connect the leads for the voltmeter and the ammeter. the small fuses rated 250vdc or higher and at 1/2 amp. or less current protect the wiring, not the meters."


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## rmay635703 (Oct 23, 2008)

My ammeter has a set of "chicken" wire I borrowed off an old 8v wallwort. Smaller than 24guage, affects meter slightly but not much, if there were to be a short the wire would pop before the ammeter. Another thought on the same problem.


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## illuminateddan (Dec 19, 2009)

major said:


> Hi illum,
> 
> I fail to see much difference. You're going to have the ammeter on the dash, right? There is going to be little difference in potential difference between the meter wires and switch wires. Yes, they are "hot", meaning connected directly to the traction pack. So treat them as such. But the potential difference between the wires is so low that a short between them would not cause an issue. Your meter wouldn't work properly, but the shunt would conduct, not the lead wires. The possibility of a ground seems no more likely with the switch on the dash as just the meter.
> 
> ...


While agree that you're still bringing hv to the dash for the ammeters my thoughts were:
if I have shunts on the +ive side of the pack, and another on the motor I will have four wires that have potentially the full pack voltage on any or all of them. Then I have two wires from this switch that go into the ammeter, which while only having a tiny potential difference between the, are still likely to be hv up to pack voltage. This gives me six wires at the dash which could potentially be pack voltage.
If I installed a DPDT relay in the engine compartment then I make 4 HV connections to that within the engine compartment and then run two to the dash, along with the 12v coil line for the switch.

Personally I'd go the relay and the two hv wires over the 6 hv wires as I know how messy dash wiring can get.

Just my two cents...


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## scott (Feb 15, 2009)

Hi all,
I'm not much for writing, so here goes.
Just reading the Febuary 2010 CURRENTEVENTS article called "Measuring Battery Current in an EV". Talks about using a Hall Effect Sensor instead of a shunt. Sounds safer, but I'm not sure about sizing output for gauges. Could someone please inlighten me? The site were they can be found is"
http://www.cy-sensors.com"
scott


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## JRP3 (Mar 7, 2008)

I agree a hall effect sensor is a better way, but finding a reasonably priced one for 2/0 cable has eluded me.


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## scott (Feb 15, 2009)

Dear Scott,

Thank you for your interest in our DC current sensor. Here is the price for your reference:

Hall Effect Current Sensor: CYHCT-C9-B800A-32
Input current: -800A ~ +800A DC
Output voltage: 0 ~ 2.5V ~ 5VDC
Power supply: +12VDC
Unit price (FOB Munich): 
1-4pcs. EUR 51.96/pc USD 70.70/pc
5-9pcs, EUR 47.23/pc
10pcs, EUR 42.94/pc
Shipment time: 3-4 weeks after purchase order
Payment term: wire transfer or visa /master card before shipment

Please let me know if you have any questions.

Best regards

John Liu
ChenYang Technologies GmbH & Co. KG
Markt Schwabener Str. 8
85464 Finsing
Germany
Tel.: +49-8121-2574102
Fax: +49-8121-2574101
http://www.chenyang.de
[email protected]


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