building 2 more 72V carts

[morvolts2]

Originally Posted by Sergio

There are better units that don't use those small "ice cube" relays and can be directly powered from the pack. They are also cheaper and available from Amazon prime:

https://www.amazon.com/gp/product/B0...G8TSLEZQ&psc=1

I don't understand why You like to criticize "Chinese" stuff but link to and use it yourself for safety functions.

So You have this whole kludge of individual cell alarms and a overvoltage monitor and still have no overvoltage protection at the cell level.

A simple BMS is a lot cheaper, around $30, and would provide not only your "alarms" but would also stop the charger if a cell gets overvoltage during charge and disable the cart if a cell gets under voltage during driving.

You have audible alarms so that a 10 yr old that has no idea what voltage,amperage or wattage is,can use this? The alarm I have set at 3.4v
which hopefully will be enough warning to get home before low battery shuts it down.
If theres a BMS that can do all that and doesnt cost 2 limbs,Im all for that.

I would need an 18S unit for my 72v pack

[keepinitreal538]

Mike, im doing one 60AH and one 100AH but haven't ordered yet. I'll have to split mine between all three trays. I need to figure out if the BMS I linked will work before i order though. i don't see anything in the online manual about the surge and continuous amp discharge rates.

[Mike from Texas]

Originally Posted by keepinitreal538

Mike, im doing one 60AH and one 100AH but haven't ordered yet. I'll have to split mine between all three trays. I need to figure out if the BMS I linked will work before i order though. i don't see anything in the online manual about the surge and continuous amp discharge rates.

I want a 200Ah setup for mine but even with these cells building my own will cost more than buying one already built.

It sure seems difficult to find a BMS that will deliver high current for any sustained amount of time. I'm working on a custom pack with team extreme carts to go in my 1998 DS cart. It ios the only one I've seen that will deliver 200A continuous, 350A for 30 seconds and 500A for 5 seconds but they are seeing if they can extend the 500A time to 10-15 seconds safely.

I don't need it for speed, I have a high torque off road cart and it gets worked hard.

[Volt_Ampere]

I really do not see the dire need for a BMS that handles the motor current! If you need low voltage shutdown, use a relay or hook into the contactor circuit. I just have a very loud low voltage alarm on my cart. My BMS handles balance and overcharge protection.

[Sergio]

Volt_Ampere, I am starting to get concerned that we assume that our posts are intended to an audience that has a basic technical foundation but in reality lots of folks read the posts and don't understand some of the conditions that affect the answers.

The low voltage alarm works well for you and it would for me as well, but it assumes that it triggers at a higher "low voltage" as it would not be safe if it only goes off when a cell reaches 3.0v.

It also assumes that you understand how many AH you have left in your pack when the alarms goes off as that will depend not only on the voltage but also on the particular Lithium chemistry.

While I get the comment about a "10 yr old" was related to simplicity, I doubt that a 10 yr old (or another casual driver) would know how far is to far or how acceleration would impact the cells.

It also means you are totally blind at this point since there will be no other "safety" that would trigger before the pack is damaged.

keepinitreal538, that place seems like a dishonest business to me.

That is a chargery BMS they have concealed the brand on the top left. They have also plagiarized the pdf manual by replacing all occurrences of "chargery" with their fake name and removing the chargery copyright paragraph entirely.

They also charge double the price you can get the real chargery.

As Volt_Ampere said those discharge current limitations are only an implementation issue, I use a 20 amp BMS to run my Leaf Lithium pack and the BMS has no relevance on the discharge current.

There are a few other builds using a similar design as mine you can research if you want to build your own.

If You want a robust BMS that has an accurate "fuel gauge", check out the Zeva BMS.

[simicrintz]

Originally Posted by Sergio

That is a chargery BMS they have concealed the brand on the top left. They have also plagiarized the pdf manual by replacing all occurrences of "chargery" with their fake name and removing the chargery copyright paragraph entirely.
They also charge double the price you can get the real chargery.

What they forgot to do was to remove the file name (if you look at the top of the manual when you open the file it still reads Chargery). Pretty dishonest

[Volt_Ampere]

Anyone here that does a "Do it yourself" conversion had better know enough about using Lithium batteries to do it safely. My low voltage alarm does monitor all of the cell voltages and it is set very conservatively. The only time it actually triggered was when I purposely let the pack get down low enough. It only triggered under load and I had plenty of capacity left to get it home to charge it. I consider this safe enough for my needs.
My buddy has a brand new cart that come with lithium and he has had the low voltage alarm on his cart come on. It did not interrupt power to the motor - probably does if you ignore the alarm. I refuse to do any conversions for people because I can't trust that they know enough to use it safely. I trust myself and my wife and we have had our Leaf pack in our cart for over four years now. Everything was developed by me for my own use.

[Pat911]

Hi Sergio & Volt_Ampere,

You are both absolutely correct. I’ve only been a member here for a very short time but I can see that most members have little to no understanding of electrical/electronic systems. But that is not their fault and it is good that they come here asking the questions and taking in the information that is provided. Hopefully if there are still things they don’t quite grasp, they continue to ask questions. What needs to be pushed strongly is the low CELL voltage cutout and that a BMS is mandatory. I can’t believe that some here are putting together packs without a BMS.

A DIY lithium pack should not be attempted by anyone that doesn’t understand or respect the dangers of using such technology. Lithium batteries are safe when used within their limits, unfortunately, too often they aren’t. I would never use a lithium battery without protection, even if I’m the only one that will ever use that battery.

Personally, when it comes to DIY lithium carts, I believe that both a low CELL voltage alarm and cutout should be included, with the cutout set below the alarm, leaving a bit of range between the two. Once the cutout is reached, that is it, no bypass, no jumpering, nothing, recharge only.

Cheers
Pat.

[Mike from Texas]

Originally Posted by Volt_Ampere

I really do not see the dire need for a BMS that handles the motor current! If you need low voltage shutdown, use a relay or hook into the contactor circuit. I just have a very loud low voltage alarm on my cart. My BMS handles balance and overcharge protection.

I’m with you. I don’t want it to shut off on high discharge current. Just do it on high or low cell voltage.


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[Volt_Ampere]

Low voltage cutout can be dangerous on some carts so be careful with that. For me an alarm is sufficient but for the general public that just drives their cart, a cutout might be necessary. I have a bunch of golfing buddies that have lithium carts that they purchased that way - and they don't really have the knowledge we have here - and they don't really need it. One guy has been towed home at least once when he ran it down a bit too far.