Don't quite understand how to use a contactor

[CGameProgrammer]

Attached is a diagram I've seen posted a few times here on how to wire up a contactor/relay to control power to the controller. I'm using the Tyco EV200 contactor which eliminates back EMF so I'm pretty sure I don't need the diode, but I don't know how to supply the correct voltage to the coil. The coil is rated for 9-36VDC with 12-24V being preferable. It uses 0.13A at 12V or 0.07A at 24V to hold the contacts closed, with a maximum inrush current of 3.8A (for 0.13 seconds) when initially closing them.

Anyway I'd be running either 20s or 30s A123s so have an operating range of theoretically 60-110V. I'd prefer not to draw only from certain battery cells since I like to keep things balanced and have no BMS for discharge. What's the best way to supply power to the coil?

 

[fechter]

I use a small dc-dc converter to run the coil. The same one runs my lights.

You could also possibly use a big resistor, but at those voltages, it will get mighty hot, so it would need to be a very large one. Depending on your voltage, we can do the math.

 

[CGameProgrammer]

I haven't been able to find a DC-DC converter that works with 100V. I know ebikes.ca will be releasing one eventually (verified by emails to Justin; it will support 100V) but at the moment I don't know if anything off-the-shelf is out there. So I may go with the resistor idea.

I had found a website that shows the formula for calculating voltage using two resistors as a voltage divider when there's a load, but the coil resistance must be variable due to the economizer so I don't know what resistors to use, or the drawbacks (waste heat and inefficiency?) of using them.

 

[Doctorbass]

About the DC-Dc ..

You could try some cheap ac-dc adaptor like lithium device charger with 10V and up output or similar..

They should work with even though they are rated from 100-240v

Mine start to work at 20V only!!.. some work.. some not.. but their advantage is that they are efficient and light! and take from .. let say 20V to 250Vdc !! perfect!!

Some surplus store usually keep some of those

Doc

 

[fechter]

Check out this thread:
http://endless-sphere.com/forums/viewtopic.php?f=16&t=2264&p=95527#p95527

 

[CGameProgrammer]

Thanks, found this laptop PSU on allelectronics. Now my question is if there's anything special I have to do before hooking up 100VDC to a power supply expecting AC, and do I need to use a resistor in series?

 

[rkosiorek]

Thanks, found this laptop PSU on allelectronics. Now my question is if there's anything special I have to do before hooking up 100VDC to a power supply expecting AC, and do I need to use a resistor in series?

no - just hook it up. the first thing these switching supplies do is rectify the AC to high voltage DC wgich is then stepped down

rick

 

[pgt400]

I have a 12v contactor, I just tap 12v off my first cell, activated when I turn on my igintion key. The current is only .1 amp too low to cause any imbalance.

 

[fechter]

Thanks, found this laptop PSU on allelectronics. Now my question is if there's anything special I have to do before hooking up 100VDC to a power supply expecting AC, and do I need to use a resistor in series?

Right, just hook it up. Some of the cheap ones use a half wave rectifier, so you may need to reverse the polarity of the input to make them work. I'm sure the one you got will work either way. Now you're set for up to 240v input.

 

[fechter]

I have a 12v contactor, I just tap 12v off my first cell, activated when I turn on my igintion key. The current is only .1 amp too low to cause any imbalance.

That would certainly work on a large pack, and I've done it that way in the past. With a small-ish pack, the imbalance could become significant depending on your riding conditions.

A dc-dc converter will boost the current going to the coil by the ratio of the voltages (less losses), so the current drain on the pack will be much less than what the coil draws.

 

[monster]

About the DC-Dc ..

You could try some cheap ac-dc adaptor like lithium device charger with 10V and up output or similar..

They should work with even though they are rated from 100-240v

Mine start to work at 20V only!!.. some work.. some not.. but their advantage is that they are efficient and light! and take from .. let say 20V to 250Vdc !! perfect!!

Some surplus store usually keep some of those

Doc

do we have a recommended ac-dc convertor that works at less than 110v?

 

[CGameProgrammer]

If the power supply draws 1.4A at 50Hz AC or 0.7A at 60Hz, what current draw could be expected with DC? Or is it not possible to guess? I'm basically wondering about the differences of a switching power supply versus a DC-DC converter.

 

[swbluto]

It'll output whatever the load demands upto the maximum current of the DC converter(Which looks to be about 5-10 amps or so at ~10 volts) at which the DC converter's current limiter would kick in which effectively lowers the output voltage or it would self-destruct because it wasn't designed to go over its maximum power handling(unlikely, but I suppose an incredibly cheap DC-DC converter wouldn't have current limiting). The "load", of course, being the current going out to whatever devices your powering. It sounds like the relay will demand less than the maximum current of the DC converter, so you'll be safe.

Anyways, think of these DC converters as "Constant voltage" supplies, not "constant current". They output a current that directly depends on the connected devices total resistance/impedance. The higher the resistance, the lower the current. Current = voltage/resistance or known as I = V/R. V being the output voltage and R being the resistance of the device in ohms. If you don't want to do the math, looking at the devices' ratings should suffice.

 

[swbluto]

I'm basically wondering about the differences of a switching power supply versus a DC-DC converter.

Oh, yeah... A DC-DC converter is a device that converts between different DC voltages. A Switching power supply is a class of DC-DC converters that converts the voltage by switching regulation as opposed to linear regulation. So a switching power supply IS a DC-DC converter. But a DC-DC converter might not be a switching power supply, but it could be.

 

[olaf-lampe]

If you want to improve the efficency of the ac-dc converter, bypass the rectifier diodes. You need to find out the output polarity of the rectifier and solder your 100V input directly to the corresponding + and - pins of the rectifier.

Did you know, that voltages above 60 DC can be deadly? I always get a bit nervous, when people without electric knowledge are fooling around with their live.

-Olaf

 

[Mike1]

Matthew, I just bought this one
http://cgi.ebay.co.uk/NEW-12V-10A-Adapter-Power-Supply-for-LCD-Cord-4PIN_W0QQitemZ130291515738QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item130291515738&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

I run it on 72V and it will run everything on my scooter (about 8 amps total). Its a little bulky though. If you don't need that kind of current then there are lots that will works. As long as they are switch mode they should be OK.

Mike.