Bit the bullet Leaf Lithium build

[ag4ever]

Originally Posted by DaveTM

Thank you for your patience and time providing me with an explanation. I really appreciate that. I like it when I have a schematic to follow.....but I like it more when I understand how it works!!

Dave

No problem, I am in the same boat as you. I am installing batteries this weekend. Charger and BMS are scheduled to deliver tomorrow.

I have a very similar question, but since mine is sepex with Regen, it is more complicated. I am not an EE, and since my Dad who was an EE passed away a few years ago, I lost my resource on figuring these things out. Luckily, he taught me a lot. At times, I only know enough to be dangerous.

[Sergio]

I have been traveling for work and have not had a chance to post.

Relay coil Diodes:

The LV and HV connections in the Zeva BMS are Solid State Relays (SSR), so the use of the fly-back diode on a relay coil (inductive load) is pretty much mandatory.

LV Relay:

That should work fine as drawn.

HV Relay:

My bad in this one, I was trying to over simplify and remove the 120v relay that signaled when the cart was plugged into the wall, in a "duh moment" I decided that I could just move the relay coil positive to the charger side, but as pointed out, that will not work.

I still don't like the idea of those relays powered all of the time, besides being a parasitic drain, it will cause premature relay failure.

My original idea which is a compromise is to run the HV relay coil positive connection that goes to the battery positive through the NO contacts of a 120v relay that is wired to the charger 120v power input.

That will keep that HV relay ON only while the cart is plugged to the 120v power source.

120v relay:

https://www.mouser.com/ProductDetail...qfqAYZNg%3D%3D

[DaveTM]

Sergio, Thanks for your post. You and all who post are really a great help. As for the fly-back diodes, what size do I need? Frankly.....I've watched about a dozen you-tube videos on diodes and how they work and why you need 'em. I can't find a video that tells me this in 3rd grade language. And the one's with music only......instant dismiss from me.

BTW...my Nephew stopped over last evening and dropped off my steel module mounting box. I have to paint it (Rustoleum) before I install. I think it came out very nice considering it was steel pulled from the scrap pile!!

[Volt_Ampere]

Nice! I just have an aluminum plate mounted on top of my batteries with aluminum angle that is held on with the threaded rods. I mounted my electronics on the aluminum plate. I still need to make a box to go over the electronics out of plexi. I just finished a new BMS design that I have to mount up when I get back to my cart in Arizona. I need a couple of relays too. My LV is just an alarm now. My old BMS had HV on a solid state MOSFET in series with the charger minus but my new BMS will probably use a mechanical relay.

[ag4ever]

Originally Posted by Sergio

Relay coil Diodes:
The LV and HV connections in the Zeva BMS are Solid State Relays (SSR), so the use of the fly-back diode on a relay coil (inductive load) is pretty much mandatory.

The coil on these relays are 1W approximately, so any 1W @ 48V rated diode should work? And it would be installed across the 2 terminals of the relay coil with the diode biased - to +, correct?

[Volt_Ampere]

You want a much higher voltage rated diode. At least 100V. I would go with a 3 amp rated diode. The golf cart places sell the proper diode for this application to go across the main solenoid. That is what I would use.

[DaveTM]

Originally Posted by Volt_Ampere

You want a much higher voltage rated diode. At least 100V. I would go with a 3 amp rated diode. The golf cart places sell the proper diode for this application to go across the main solenoid. That is what I would use.

Who woulda thought of that? Actually using a factory part?

[Sergio]

You typically size a diode for fly-back operation based on the coil current since that is what will control the stored energy that can potentially be induced.

There is no downside for going bigger than needed (if you already have a diode), but no advantage either.

Since those relays have a 25mA coil current, a simple 1N400x diode (1 amp) will work fine.

Those things are so cheap You can buy a "lifetime supply" of them from Amazon by the time you add shipping from a electronic supplier:

https://www.amazon.com/McIgIcM-1N400...eywords=1n4007
or
https://www.amazon.com/100-Pieces-1N...s=1n4007&psc=1

They need to be installed between the 2 relay coil contacts with a "reversed bias" orientation, meaning the cathode (side with the stripe or band) goes towards the positive activation wire.

Another cool idea (I am full of them when I don't actually have to do the work) would be to wire another 48v relay to provide an automatic "Sleep mode" for the BMS.

You would wire the "sleep" terminal to the battery negative through the NC contacts of a SPDT relay.

The new relay coil would connect to both the LV and HV positive activation wires by the way of a diode from each relay coil to keep them isolated (same 1N4007 diode).

That would activate the new relay when either the Key Switch is ON or the Charger is plugged IN and it would break the Sleep wire connection to negative.

When both the key switch is OFF and the charger is not plugged, all relays would be OFF and the BMS would automatically be put to sleep (NC contacts would be closed) which will eliminate most of the drain from the pack.

[ag4ever]

Originally Posted by Sergio

You typically size a diode for fly-back operation based on the coil current since that is what will control the stored energy that can potentially be induced.

There is no downside for going bigger than needed (if you already have a diode), but no advantage either.

Since those relays have a 25mA coil current, a simple 1N400x diode (1 amp) will work fine.

Those things are so cheap You can buy a "lifetime supply" of them from Amazon by the time you add shipping from a electronic supplier:

https://www.amazon.com/McIgIcM-1N400...eywords=1n4007
or
https://www.amazon.com/100-Pieces-1N...s=1n4007&psc=1

They need to be installed between the 2 relay coil contacts with a "reversed bias" orientation, meaning the cathode (side with the stripe or band) goes towards the positive activation wire.

Another cool idea (I am full of them when I don't actually have to do the work) would be to wire another 48v relay to provide an automatic "Sleep mode" for the BMS.

You would wire the "sleep" terminal to the battery negative through the NC contacts of a SPDT relay.

The new relay coil would connect to both the LV and HV positive activation wires by the way of a diode from each relay coil to keep them isolated (same 1N4007 diode).

That would activate the new relay when either the Key Switch is ON or the Charger is plugged IN and it would break the Sleep wire connection to negative.

When both the key switch is OFF and the charger is not plugged, all relays would be OFF and the BMS would automatically be put to sleep (NC contacts would be closed) which will eliminate most of the drain from the pack.

I think you and I are on very similar pages with how to wire these relays. I did not think of adding one for the BMS, but I was planning to have it wired to the main pack disconnect so when it was unplugged it would kill the draw. The only down side I see is the energy capacity stored in the pack is monitored by the BMS and when the BMS looses power, that energy capacity is lost, so it would require another discharge/recarge cycle to have accurate energy capacity readings. At least I think the ZEVA works that way.

Have you seen my post on the Extreme DC threads?

http://www.buggiesgonewild.com/extre...ay-wiring.html



I was planning to wire mine up like this, but I am not sure I really need the HV protection for REGEN since I don't live at the top of a hill, and the laws of conservation of energy dictate I will not be putting more in the batteries than I take out. Again, assuming I don't charge it on a hill and roll to the bottom.

This diagram does not have the flyback diode shown. I need to re-sketch to include that diode.

[Volt_Ampere]

I am not sure I would wire things like that. The charger may not like being connected to the battery with no 110V input. My BMS interrupts the charger DC output not the AC input. I also would not depower the BMS while it is connected to the cells. It may not hurt it but some electronic designs don't like voltages applied with the power off. Check with the BMS designer about that.