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StudentEV's Daihatsu Conversion

Posted: Thu, 16 May 2013, 20:43
by Johny
StudentEV wrote:A silly question maybe, can I run a 110VAC charger from my 125VDC traction pack? While the car is running? Possibly the Raider charger I posted earlier...
There are no silly questions - just smart asses who make you feel bad when you ask something you really don't know. Anyway - soapbox off - it depends on the device. Mains type thingys that state 110 VAC or 240 VAC (one or the other) won't run off less than about 200 VDC. Devices that state a range from 110 to 240 VAC (with no switch or user intervention required) will run off a wide range of DC voltage.

The reason is that the former devices use a trick to double to input voltage using diodes and capacitors and the trick doesn't work on DC.

The latter devices are a lot smarter. That's why I picked laptop chargers as a candidate. The eBay add said 100-240VAC. I'd be double checking by contacting the seller (often fraught with cross language issues) but I'm pretty sure they'd be OK.

StudentEV's Daihatsu Conversion

Posted: Thu, 16 May 2013, 22:54
by BigMouse
Regarding DC-DC converters, you do have to be careful. Some larger switch-mode power supplies actually rely on the AC at the input across a small transformer to power the control and gate driver circuits. Not all of them can start without AC present. Many computer power supplies are like this.

The idea of using a SMPS battery charger is a good one though, especially if it is "world voltage" capable as Johny describes. I'd be looking for something around to 50-75amps though. For a Handi though, 20a should be fine.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 04:10
by StudentEV
OK I'll be sure to double check any ebay purchase for input type.

while I was searching ebay for a multimeter I came across this meter that I thought might be useful for most of the measurements I'll need:

Instrumentation idea

Only issue is we'll be running 125V, 5v over the max stated... Is it worth the risk to check if it runs anyway? Or should I try find something better?

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 05:07
by StudentEV
Also wondering if it would do instead of a discharger for my battery testing, might need to pm antiscab on that one...
EDIT - Scrap that, min voltage 5v, cells are 1.2

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 15:59
by Johny
It looks very useful for battery testing but as a car instrument it appears to me like it would not read over 120.0 volts. The specs say 120.0. It wouldn't hurt to ask the seller if it reads above 120V. I tend to ask a LOT of questions of eBay sellers - sometimes with an understandable result Image
The minimum voltage is the voltage is is powered from - not measured. It'll measure down to 0. A useful device I think.

Power Supply      5V~40V (external/Internal power supply)
Measuring range      (1)Volt 0~120.0V / Amp 0~30.0A, external power supply
(2)Volt 5~40.0V / Amp 0~30.0A, Internal Power supply

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 16:43
by evric
But it only measures up to 30 amps with internal shunt. No good for an EV. It would be great for battery testing if it included load switching at a predetermined voltage... you'd be better off with a JLD... series meter with external shunt.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 17:09
by Johny
evric wrote: But it only measures up to 30 amps with internal shunt. No good for an EV. It would be great for battery testing if it included load switching at a predetermined voltage... you'd be better off with a JLD... series meter with external shunt.
The same seller has a version that does 500 Amps so the current isn't a problem. But the highest voltage is 120V. Evric's right though. You need an automated cut off of some description. That can be done fairly simply using a comparator and relay but I'm not sure when you are going to start testing the cells.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 17:15
by Johny
The 500A version has a relay outout and the seller indicates one use as "Intelligent battery discharger".

Edit: I have asked the seller what the relay output can be used for.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 17:22
by unheardofinstruments
Nevilleh has designed a great amp meter that doesn't require high voltage in the cockpit. He is a bit under the weather atm but check out the thread and for about 99 bucks he will build one but not for a while until he gets better. It is open source and he has the info zipped up here;
viewtopic.php?title=wanted-an-amp-hour- ... 68&start=3

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 18:34
by Johny
I got an answer from the seller.
They have a similar type (this one is 90V, 100A) that actuates the relay on lots of different conditions.
http://www.ebay.com/itm/181145374805

By turning External device Relay on and off, it can control external devices, such cut off Power Input
[OVP] Over Voltage protection
[LOP] Low Voltage protection
[OCP] Over Current protection
[OAH] Over Charge protection
[OPP] Over Power protection
[OFT] Over Time protection


Pretty useful device for non-automated, but safe discharge, cell testing.


StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 18:35
by StudentEV
Johny wrote: It looks very useful for battery testing but as a car instrument it appears to me like it would not read over 120.0 volts. The specs say 120.0. It wouldn't hurt to ask the seller if it reads above 120V. I tend to ask a LOT of questions of eBay sellers - sometimes with an understandable result Image
The minimum voltage is the voltage is is powered from - not measured. It'll measure down to 0. A useful device I think.

Power Supply      5V~40V (external/Internal power supply)
Measuring range      (1)Volt 0~120.0V / Amp 0~30.0A, external power supply
(2)Volt 5~40.0V / Amp 0~30.0A, Internal Power supply[/]


OK excellent, good spot. Here's a link to the 500A version:

120V 500a METER

Incidentally, Matt informs me that the usable voltage of the pack will be only 120V as it's used. Alternatively, I could bypass four cells.

IS the cut off an emergency thing? Or to cut off load before cells drop below x voltage?

I also found this monster, designed for RC Cars but can handle the battery technology and claims to balance the cells??? Up to 15 of them!

I just can't figure out if it has an amp hour count - this would solve the tesing problem - and maybe 7 of them could be a traction pack charging solution? I could be way off here, but here are the links:

EDIT I've asked the seller about amp-hour-count

IMAX CHARGER/DISCHARGER EBAY

Details on website

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 18:52
by Johny
StudentEV wrote:I also found this monster, designed for RC Cars but can handle the battery technology and claims to balance the cells??? Up to 15 of them!
Not sure it can balance NiMH cells. Do they need balancing?

Current drain for balancing LiPo: 300mAh/cell

To my way of thinking you have two separate requirements:

1. Selecting good cells from the pile you have.

2. In car charging and monitoring.

I think you probably have to isolate these two and not try to share systems. My first priority would be to design the testing mechanism for your cell selection. Only a 1A discharge rate probably isn't enough to determine a cell's suitability for an EV.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 19:21
by StudentEV
Thanks John, just saw your earlier reply. I think I'll get that one for testing. It is the first priority.

Is the consensus that even the 120v 500A one would be no good as instrumentation?

EDIT: After reading it again I think the imax only balances lithium cells.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 19:41
by Johny
StudentEV wrote:Is the consensus that even the 120v 500A one would be no good as instrumentation?
As it stands no good. I get the feeling that this seller actaully makes these. Ask them if you could get one that went up to 150 VDC.
EDIT: After reading it again I think the imax only balances lithium cells.
I got that impression too. But I am not sure if you really need balancing as such with MiMH. The Prius doesn't balance to a cell level. I think it might be done with low current or some such for a period of time but not monitoring individual cells.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 20:06
by StudentEV
Johny wrote:
StudentEV wrote:Is the consensus that even the 120v 500A one would be no good as instrumentation?
As it stands no good. I get the feeling that this seller actaully makes these. Ask them if you could get one that went up to 150 VDC.
EDIT: After reading it again I think the imax only balances lithium cells.
I got that impression too. But I am not sure if you really need balancing as such with MiMH. The Prius doesn't balance to a cell level. I think it might be done with low current or some such for a period of time but not monitoring individual cells.


Yeah I'm under the impression that you just hope for the best and take out the dead cells when the pack voltage drops enough... Just regular testing. I thought this might solve the problem but even if it could, it might stretch the budget!

I have asked the seller the question.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 20:14
by StudentEV
I got a reply, they can customise one to 150V.

I've avoided the question of current for fear of seeming like a total noob, which I am, but now I have to tell him.. How do I know what the current will be for the system?

Motor is rated at 98A but we're running a higher voltage.. I'm just not sure how to calculate it...

Any other requirements I need that aren't part of the 120V 500A version??

Is it possible to use this one for testing AND instrumentation?

I would be lost without you lads.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 20:17
by Johny
It looks like just a slow charge to balance NiMH.
http://www.camlight.com/techinfo/techtips.html

I still think you need to do some pre-selection on the cells just to save time even early on. It will also help establish a cell capacity for you to work with. Numbering cells that are not discarded during the selection process will help greatly as well.

Have you cherged/discharged any cells yet?

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 20:29
by Johny
StudentEV wrote:I've avoided the question of current for fear of seeming like a total noob, which I am, but now I have to tell him.. How do I know what the current will be for the system?

Motor is rated at 98A but we're running a higher voltage.. I'm just not sure how to calculate it...
You will probably end up at about 4 times motor current - around 400 Amps but it will totally depend on what you battery pack can deliver.
If you can't get about 30kW out of the drive train then the car probably isn't drivable in traffic. At 120V, that's 250 Amps.
I'd go for the 500A version.
Any other requirements I need that aren't part of the 120V 500A version??

Is it possible to use this one for testing AND instrumentation?
Kind of, but the high current rating means it will be woefully inaccurate at low current. Is it possible to buy 2 shunts? A 50 Amp and a 500 Amp. Then is it possible to re-calibrate the device for either shunt yourself? Alternatively just ask if the 50A and 500A shunts produce the same voltage (mV) for a given current (100A on 500A shunt drops same voltage as 10A on 50A shunt). If it does, just get 2 shunts and manually divide by 10 when reading during the testing.

OR

Since shunts are specified as X mV for Y Amps, just buy another one somewhere else that is a tenth (or more) of the 500A with same mV rating (eBay - lots).
I would imagine that you will be esting cells at under 10A.
Do you have any idea of cell rating in AH for the cells you have?

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 20:58
by StudentEV
Cool, alright well it sounds like a separate solution to both problems. 90V one for testing, 150v 500A meter for instrumentation. Or a separate shunt.

Yes the plan is to go through and test all the cells that aren't obviously dead, and consolidate the pack - keeping some spares. This is until we get it on the road and we might look at adding another pack in parallel or running all the cells in parallel to increase range.

They are rated at 30ah but Matt (antiscab) thinks usable capacity will be 20ah-25ah depending on their condition, we won't know until testing.

I haven't charged or discharged any yet, I'm waiting on a multimeter to arrive and I needed something to calculate amp hours while charging/discharging. And I need a charger.

StudentEV's Daihatsu Conversion

Posted: Thu, 23 May 2013, 21:42
by Johny
StudentEV wrote:They are rated at 30ah but Matt (antiscab) thinks usable capacity will be 20ah-25ah depending on their condition, we won't know until testing.
Did Matt indicate possible safe discharge rates? You may have to parallel at least two cells (make cell pairs) to get the current capacity up. In that case you might be looking at chasing down more cells or lowering the expected pack voltage.

StudentEV's Daihatsu Conversion

Posted: Fri, 24 May 2013, 00:18
by antiscab
Hi Guys,

Those 30Ah nimh cells will only put out ~150A for a little while and 200A under some circumstances (basically fully charged and warm)

Two packs will be needed

as far as balancing goes, bottom balancing is the best for nimh
self discharge on these cells is high, and increases with both temperature at state of charge. so if you leave the pack full, you will find it unbalanced fairly quickly

The other issue is they have memory effect, so keeping them flat helps to sort that out.

I would suggest as part of the testing process, at the end discharge the cells to 0.5v and then leave them that way until you assemble the whole battery

You can only parallel nimh on discharge, the two strings will need to be charged separately

Matt

StudentEV's Daihatsu Conversion

Posted: Fri, 24 May 2013, 00:27
by Johny
So don't parallel them at a cell level. Make two equal strings and join them when flat. Design battery current limit 250-300A.

StudentEV's Daihatsu Conversion

Posted: Fri, 24 May 2013, 06:09
by StudentEV
Thanks Matt, Thanks John.

Matt gave me another contact in Melbourne for cells but I haven't been able to get a hold of him yet, I thought we could get away with one pack but guess I was wrong!

Yeah I have a pretty solid idea of the testing process now, and picked up some tools today to help me get at the dead cells and remove them. There aren't all that many bulged ones which is a good start, I think.

Will still need a charger to get the process started - any recommendations for a cheap-ish one matt? I looked at the West Mountain but a bit out of my price range. With the cheap combo meter I should be find to check amp hours going in and out, but I haven't found a charger suitable. Could I use alligator clips on a charger designed for something else? another charger? Or run a 240V power adapter as a charger?

Just to confirm - running two sets in parallel takes us from 20-25ah useable to 40-50ah usable right? The current doubles, voltage stays the same and in StudentEV (layman's) terms, we end up with a car that's a little heavier but goes further. Right?

StudentEV's Daihatsu Conversion

Posted: Fri, 24 May 2013, 07:00
by neilg
Had a quick look on ebay and found the following NiMH charger.

[url=mailto:http://www.ebay.com.au/itm/BA6C-80W-Pro ... ed9&_uhb=1]BA6c 80w PRO Charger[/url]

It is:
Mains powered
Charges at up to 6 Amp
Up to 18 NiMH cells (probably not at 6A)
Discharges at up to 2A
1-5 cycles of charge/discharge
Shows graph of voltage, current, capacity and temperature curves via a USB connection.

It lists for $47.65 with free postage.

I have not used this charger so don't know how good it is.

Hope this may help
Neil

StudentEV's Daihatsu Conversion

Posted: Sun, 26 May 2013, 05:08
by cobber
Hi,
I am in Melbourne and have Vectrix Ni-Mh cells that you can have cheap. I know of chargers that you could but that would suit. Conatact me and I would like to help with your project.
Paul