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Unread 05-15-2019, 09:29 AM   #1
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Default Lithium conversion basics

I plan to convert to Lithium. I have read a lot on here, but still have questions. Can you guys help me with some basics please? I have a custom 72V D&D motor with an Alltrax 500a 72500. And all upgraded other components. It seems I will need 10 leaf modules (2 cells per module, 4.17v per cell) giving 83.4v total. (seems 9 leaf modules would be 75.1v and I guess thats not enough?)

When I order the batteries, will I need to configure the connections (how they are wired together)? Do they come with any of the bus bars? Or whatever those plates are that connect the batteries to each other. If not, where do I get those?

I assume I need allthread to bolt all of the modules together and some form of a vented box for them. Any tips on that is appreciated.

I assume when I order the BMS, it will come with instructions. Will it come with the other items I have been reading about like shunts, disconnect, relays, fuses, etc,

I will also want a charger with overcharge protection. It seems the controller may somehow help with that, but I want as many failsafe measures in place as possible. Once this is built, I want it to be super safe and super hands off.

Thanks for any input on this.
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Unread 05-15-2019, 01:28 PM   #2
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Default Re: Lithium conversion basics

Keep researching. There are some good build thread you just need time to read through some.
DIY 101 - 14 cell Nissan Leaf lithium pack
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Unread 05-15-2019, 01:33 PM   #3
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Default Re: Lithium conversion basics

Quote:
Originally Posted by somfas View Post
(seems 9 leaf modules would be 75.1v and I guess thats not enough?)
Your 72v lead acid, fully charged would be around 76v. Most people converting to lithium opt for higher V than the lead acid reached at full charge. But since you are already 72V this may not be as important to you. Your controller will work with either 10 or 9 cells. 10 cells give you 83v to 60v and 9 gives you 74.7v down to 54v. 10 cells will give you more available watts so you should be able to get a little better range on 10.

Quote:
Originally Posted by somfas View Post
When I order the batteries, will I need to configure the connections (how they are wired together)? Do they come with any of the bus bars?
Depends on who you buy from. Some will give you buss bars, some won't and you'll have to make your own.

Quote:
Originally Posted by somfas View Post
I assume when I order the BMS, it will come with instructions. Will it come with the other items I have been reading about like shunts, disconnect, relays, fuses, etc,
Most likely it will not come with a disconnect, relay or fuse. The shunt is possible depending on which BMS you get and what options, but a shunt isn't a requirement to go lithium, it's an option.

Quote:
Originally Posted by somfas View Post
I will also want a charger with overcharge protection. It seems the controller may somehow help with that, but I want as many failsafe measures in place as possible. Once this is built, I want it to be super safe and super hands off.
The charger can be set to stop at a certain max V, but it won't know the individual cell voltages. My charger is set to stop charging at 57.6v which would be 4.12vpc if all cells are balanced. The charge termination is also controlled via the BMS. If you set the BMS to stop at 4.15vpc then you'll have two charge stop mechanisms. The controller is not involved in stopping the overcharge.

As for undercharge, that is where you can program the controller as another fail safe. I have mine set to stop when it gets to 45.5v which is 3.25vpc. If you have your BMS also set up to somehow trigger a relay that cuts power to your controller then you can use that as a second method to stop power drain.

Welcome to the lithium addiction!
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Unread 05-15-2019, 01:38 PM   #4
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Default Re: Lithium conversion basics

Also, lithium doesn't like over charge, over discharge or over heat.

I run my lithium pack up to 4.12vpc and down to 3.25vpc. Most people charge higher and discharge lower. The max that is considered safe (on paper) is 4.2vpc down to 3.0vpc, but you will get longer life it you don't go that far. My pack limits are probably more conservative than need be, but I am ok with that.
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Unread 05-15-2019, 04:33 PM   #5
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Default Re: Lithium conversion basics

Thanks very much for that thread link and all the detailed info. That helps!
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Unread 05-16-2019, 05:39 AM   #6
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Question Re: Lithium conversion basics

I received my 14s/7module leaf set yesterday and am still waiting for my BMS and charger. I have been thinking of running my BMS strictly for charging so as to bypass the low voltage cutoff by the BMS. I am going to install a digital meter to warn me, but I do not wish to get stranded somewhere if the BMS decides that my battery is too low. I realize that some on here have great reasons for NOT bypassing the BMS for discharge, but I only want the BMS for balancing during the charge.
I have a pretty good idea as to how to wire the BMS this way, but would really appreciate it if someone could post a simple wiring drawing of how to use the BMS for charge balancing only. I want make sure that I get the wiring correct. B-, P-, etc are new to me and I am still studying this stuff before my BMS arrives.
I have not read EVERYTHING on this site regarding the use of lithium power, so if this is repetitious, please just point me in the right direction.
Thank you
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Unread 05-16-2019, 06:15 AM   #7
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Default Re: Lithium conversion basics

As stated above READ READ READ and when you have totally confused yourself read some more lol

As you go up in voltage on your pack the amp draw will go down which will greatly increase your range. I would go with as much voltage as your system will handle and you can physically fit. With that said comes the issue of finding a BMS that will ballance a high voltage pack and still be vehicle friendly. Options exist but i think you'll find that some level of compromise will need to be made in your particular situation. The cheapest option will be to use a BMS that is not directed toward mobility but more towards off grid power storage. Do not purchase a BMS that flows output current through it! These things are everywhere and are crap for vehicle applications the current limits are in most cases way to low for this type of application.

Zeva has a system that fits your configuration. http://zeva.com.au/index.php?product=131

A lot of us here have gone with some sort of Zeva setup. The customer service is second to none and the documentation is pretty good. The info available on the site is extremely helpful as well have a look around while you are there.

If you send an email to zeva directly with your application specs they will provide you with a ton of feedback and suggest a setup for you.

Good luck with the build!!
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Unread 05-16-2019, 08:52 AM   #8
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Default Re: Lithium conversion basics

If you opt to not go with an LV cutoff by BMS you can get a cell monitor with an audible alarm. I purchased two of these but haven't hooked them up yet...

https://www.amazon.com/dp/B00XQ91ECA...e-f767610a7f33
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Unread 05-16-2019, 09:14 AM   #9
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Default Re: Lithium conversion basics

Even with the cheap BMS that was designed to have the current go through it You can use a $7 relay to provide LV and HV cell protection while motoring without having the current go through the BMS.
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Unread 05-16-2019, 10:45 AM   #10
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Default Re: Lithium conversion basics

I am thinking of just using the BMS for charging protection, HV. I will use an LED voltage monitor with an alarm to watch for low voltage. Normally, I just count on an analogue voltage meter, but I don't think they will do me much good with lithium.

Regarding the use of the BMS for charging only, I am guessing that I run my power normally with the BMS connected to the battery and to the charger. The power will not be interrupted by the BMS, but the batteries will be charged using the BMS as a governer-limiter. All I need to do is make sure I get the positive and negative leads soldered in the right places.
When I decided to make the leap to lithium, I had no idea that it would entail a whole new educational lesson.
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