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EZwryder
25 November 2011, 1606
I have a hi-volt contactor on the B+ side of my DC-DC converter. I would like to tap 12 volts off the battery pack for a momentary pulse to energize the coil and close the contactor. I would then "key on" the bike, allowing the 12 volt output of the converter to keep the contactor closed.

I've attached a simple schematic and would appreciate input from anyone who has some circuit design experience. Do I need to add anything to this? (I know I need some safety components. I left those out for simplicity.)

For a brief moment, the coil will have two roughly equal voltage sources applied to it, but they'll be in parallel, so I don't see an issue there. But I know what I don't know...and I don't know if there are hidden problems with this. Your thoughts would be appreciated. Thanks in advance.

d.

2052

lugnut
25 November 2011, 1856
Interesting idea. Looked like it might work. So I just tried it on the bench and it does seem to work. I have a Vicor DC/DC, 48 in/12 out. A 14 cell LiPo. Omron contactor, 80A, 12V coil. I tapped off 4 cells which were about 14V. It brought in the contactor which then turned on the DC/DC which then powered the contactor after I disconnected the 14V from the coil. So it works as a latch circuit. It did not seem to matter which 4 series cells of the 14 I would use.

The Vicor DC/DC is isolated, which is probably necessary as not to get reverse current. And also your circuit would leave the high voltage connected to the low voltage which could be eliminated by using a double pole push button, which I would suggest.

Good idea, I think. It could be a problem if your DC/DC browns out or faults out because the main contactor could open under load.

podolefsky
25 November 2011, 1936
Looks good to me. Cool idea.

I don't see anything wrong with having 12V from the pack connected to the DC-DC output for a moment. People use DC-DC converters to charge a 12V system battery, and those sit on the output full time.

I 2nd what lugnut said about double pole switch. Definitely want to completely disconnect the pack from DC-DC output.

Make sure everything is properly fused and you should be fine.

EZwryder
25 November 2011, 2122
And also your circuit would leave the high voltage connected to the low voltage which could be eliminated by using a double pole push button, which I would suggest.

Good idea, I think. It could be a problem if your DC/DC browns out or faults out because the main contactor could open under load.

Thats a good catch, thank you. I think I will wire it up and try it out for a while. Maybe if I put a big cap on it that would offer a little protection against a load induced voltage sag.

podolefsky
25 November 2011, 2148
Thats a good catch, thank you. I think I will wire it up and try it out for a while. Maybe if I put a big cap on it that would offer a little protection against a load induced voltage sag.

The problem of contactor opening under load would be there with any design that drives the coil from the DC-DC converter.

You would have to use a really big cap, over 1F to keep a typical 12V contactor closed for 1 sec. Better to use a small 12V battery. That would eliminate the issues with pack voltage plus it's redundant.

I believe you're using a Curtis 1238? Usually those are paired with a 24V contactor, driven by the controller (they apparently won't work with a 12V contactor). I've got my Curtis set up so that the run/kill switch will break the connection from the controller to the contactor. I have a latching relay circuit, triggered by the start swtich, that turns on the controller. My DC-DC is always on (but I have a switch that will turn it off for storage...the current draw is very small with no load).

Here's my circuit diagram (http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/electric_motorcycle_wiring_AC_21.pdf).

Jack Riggi
26 November 2011, 0116
Are you using the start/stop switch your stock handlebars? You say you use a latching relay circuit, triggered by the start swtich, that turns on the controller, is that also the stocks start switch button on the handle bars that normally just starts the bike? Do you have an emergency disconnect or do you just use the stop start switch for emergency disconnect? Nice schematics you did on your bike Noah! I sure wish I wasn't still a newbie at this because you're schematics are well wrote and tells everything which you did and what I need to do basically, but I just can't grasp and understand it all yet at this time in life.

podolefsky
26 November 2011, 0125
yup, it's the stock start switch, and the stock run/kill switch, both on the right handle controls.

the run switch only has to break 24V going to the contactor, so that's my safety valve.

(we were all newbies at some point, and i still have a lot to figure out...just keep working at it and it'll start coming together).

lugnut
26 November 2011, 0636
Thats a good catch, thank you. I think I will wire it up and try it out for a while. Maybe if I put a big cap on it that would offer a little protection against a load induced voltage sag.
Watch putting big caps on the output of switches. It will cause the switch contacts to arc and maybe weld. Occurred to me this morning that your circuit does not show any precharge which you should have if your main contactor load is a motor controller.

EZwryder
26 November 2011, 0812
I believe you're using a Curtis 1238? Usually those are paired with a 24V contactor, driven by the controller (they apparently won't work with a 12V contactor). I've got my Curtis set up so that the run/kill switch will break the connection from the controller to the contactor.

That's a nicely done schematic. I'll have to look over it in more detail for some more ideas. This is actually a second contactor. I do have the Curtis 1238 and I have a LEV 2xx somethingorother with the 24v coil.

The contactor on this circuit is a smaller Tyco unit that I had laying on the shelf. I'll eventually replace this converter with a Vicor but regardless which unit I use I just like the idea of having everything disconnected from the main pack any time it is sitting still.

EZwryder
26 November 2011, 0825
I sure wish I wasn't still a newbie at this because you're schematics are well wrote and tells everything which you did and what I need to do basically, but I just can't grasp and understand it all yet at this time in life.

Jack, if it's any consolation, I studied circuits for two years at vo-tech school in high school and I didn't realize how much I'd forgotten until I started working on this bike. I have had to ask some pretty basic questions to refamiliarize myself with some of the aspects of e-bike building and there are many patient and knowledgeable people here.

One thing to keep in mind is that many of the schematics you see are showing multiple sub-systems and once you are able to separate them in your mind, any individual part is pretty simple. For example, when I did the first build of my bike, it had just three components, a set of batteries, a motor and a controller. I had two safety devices on it, a contactor and a fuse. I had one controller, a twist throttle. That's it.

In many of these designs, the builders have integrated the electrical powertrain with the bike's original 12 volt circuit. If you saw Noah's schematic without the bike's 12 volt systems, you would see the e-bike is a much simpler system than it appears. In my first build, I kept the powertrain and the bike's 12 volt system completely separate. I just used the bike's original 12 volt battery to power the lights.

d.

EZwryder
26 November 2011, 0833
Watch putting big caps on the output of switches. It will cause the switch contacts to arc and maybe weld. Occurred to me this morning that your circuit does not show any precharge which you should have if your main contactor load is a motor controller.

This is a secondary contactor controlling just the 72v to the DC-DC converter. I don't think I'll mess with the cap. I'll just run it as is and see what it does!

d.

podolefsky
26 November 2011, 1240
That's a nicely done schematic. I'll have to look over it in more detail for some more ideas. This is actually a second contactor. I do have the Curtis 1238 and I have a LEV 2xx somethingorother with the 24v coil.

The contactor on this circuit is a smaller Tyco unit that I had laying on the shelf. I'll eventually replace this converter with a Vicor but regardless which unit I use I just like the idea of having everything disconnected from the main pack any time it is sitting still.

I see! So this is only to turn on the DC-DC...in that case, nicely done.

Vicors have an input pin that will disable when connected to ground (and enables when floating). So once you have the Vicor, all you need is a little switch to ground and you're set. On mine, I modified the key switch so that turning to "park" disables the Vicor.



In many of these designs, the builders have integrated the electrical powertrain with the bike's original 12 volt circuit. If you saw Noah's schematic without the bike's 12 volt systems, you would see the e-bike is a much simpler system than it appears. In my first build, I kept the powertrain and the bike's 12 volt system completely separate. I just used the bike's original 12 volt battery to power the lights.

Yup, there are 4 main parts of my diagram. 12V system, Motor system, battery/BMS, and on the right is a diagram of the wiring harness. The wiring harness repeats a lot of the stuff on the left. I drew it because I built the 12V system from scratch.

Jack Riggi
26 November 2011, 2046
Thanks for trying to make me fell better about not knowing whay I am doing! that is a big problem for me, U took it in school & forgot more then I ever learn because I never took electric class at all in high school I asked to take electic & they said flat out NO! U need to take auto2 for your last year so no electric class of any kind for me all my life now I am 57 years old & just now starting to learn about electric's. alot different then Union Ironwork I did for 36 years right out of high scool at the age of 18, There are so many things I need to ask about but just don't have a clue what or how to ask about! Total new way of doing things all electric after working on ICE motor all my like! but I know electic is easyer to work on & a lot less things to keep fixing but still very new & totaly different!!!! just starting out! at least I learned how to weld good after 41 years!! that helps out a lot to work on electic bikes & ev's of all kinds. but I will get my bike dome some time just a lot slower then I thought! not knowing any thing about watt & amps different voltage , relays of all differrent type! but slowly I will get it with the help I get from all my new friends on EL-Moto!