10-23-2019, 07:58 AM | #11 |
Gone Wild
Join Date: Jul 2018
Location: Central Ohio
Posts: 1,720
|
Re: first step in DS conversion to lithium seems easy
Keep in mind I am, at best a novice when it comes to electrical...
It seems plausible to me that this BMS can utilize the MOSFETs to cutoff for over charge and over discharge. I know that todays lithium powered hand tools (drills, impact guns, etc.) utilize MOSFETs to protect the batteries from these events. I am just not seeing in the data sheets if it specifies for sure if it does or not. Let alone, at what voltage(s) it would do so. Are you able to adjust any settings, through a monitor or computer? Hopefully a guru will be along shortly so we can all learn... Last edited by BBBHC; 10-23-2019 at 08:19 AM.. Reason: added bolded sentences |
Today | |
Sponsored Links
__________________
This advertising will not be shown in this way to registered members. Register your free account today and become a member on Buggies Gone Wild Golf Cart Forum |
|
10-23-2019, 08:31 AM | #12 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,192
|
Re: first step in DS conversion to lithium seems easy
I have not seen a BMS that can handle LVC and HVC without external relays. The mosfets can't handle the current they would be seeing. The HVC has to interrupt the charge current and the LVC should interrupt the main drive current by opening the contactor. I do not use an active LVC on my cart - just a very loud alarm.
|
10-23-2019, 08:34 AM | #13 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
|
Re: first step in DS conversion to lithium seems easy
One of the functions of a BMS is to monitor individual cell voltages (not pack voltage) and stop the charge or discharge of the batteries if the voltage is outside the specified range, either higher or lower.
There are many ways to implement the "disconnect" function, the type of BMS you have is really designed for E-Bikes that have much less discharge current. The FETs themselves are not the issue, thermal management is the real problem since FETs have a small resistance when conducting and can get very hot during high current discharge. You also have the issue of the circuit board copper trace, which appears to have been "solder augmented " in your picture, having to carry the controller current without melting. I think the best approach to use that BMS with a Golf Cart is:
Cold Side of key switch is the same as the switched side or the side that only has power when You turn the key switch ON. That will allow the BMS to disconnect the charger in case of a charging issue and disable the cart in case of a high/low cell voltage condition by essentially turning the key switch OFF. Depending on your situation You can also add another inexpensive 120v coil relay to disable the cart from operating when the onboard charger is connected to AC power. |
10-23-2019, 08:41 AM | #14 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
|
Re: first step in DS conversion to lithium seems easy
FWIW....these are the relays I am using. Cheap and effective. Remember that these are 48-V relays.https://www.mouser.com/ProductDetail...rrencycode=USD
|
10-23-2019, 01:19 PM | #15 | |
Getting Wild
Join Date: Sep 2015
Location: Lake Worth, FL
Posts: 76
|
Re: first step in DS conversion to lithium seems easy
Quote:
The BMS still manages the charging in its usual way, which I guess it's able to do because the amperage is so much lower than the discharge amperage? If I use a 12vac relay as you suggest to protect the battery during charging, then I guess I could use the lowest capacity (least expensive) BMS available for this? |
|
10-23-2019, 01:37 PM | #16 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
|
Re: first step in DS conversion to lithium seems easy
You got it, as You have drawn the BMS is already providing charging protection since the charger current has to go trough the BMS P- before reaching the pack negative.
When the BMS senses a high cell voltage during charge it can stop the current flow from P- to pack negative so the charger can no longer charge the batteries. The 120vAC relay is in case You want to prevent the cart from driving while you have an extension cord plugged in the cart. I think a good Solution would be to use one of theses SPDT relays: https://www.amazon.com/Zettler-Minia...SC8/ref=sr_1_4Wire the coil terminals in parallel with your charger AC input so it gets powered when the cart is plugged to AC power, wire the contacts as follows:
That way when the AC cord is not plugged to the cart, the 48v relay is connected to the BMS P- and the charger is completely isolated from the battery pack. When You plug the AC cord, the 120vAC Relay gets energized and the BMS P- gets connected to the charger output and the 48v relay cannot be energized to drive the cart. If they make a version of that BMS with only 50 amps capacity it should work just for charging. |
10-23-2019, 03:04 PM | #17 |
Getting Wild
Join Date: Sep 2015
Location: Lake Worth, FL
Posts: 76
|
Re: first step in DS conversion to lithium seems easy
Now I understand about the relay to stop the cart from moving while it is charging. Thanks again.
The BMS is not programmable, I'll check the seller's eBay listing tonight to see if it specifies the high and low voltage cutoffs. |
10-23-2019, 06:37 PM | #18 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,192
|
Re: first step in DS conversion to lithium seems easy
I looked into using Solid State Relays (FET's) and I found that to handle the charge currents I am using required a fairly expensive one with a heatsink. I went with a conventional automotive relay that was very inexpensive and does the job to interrupt the charging current if my BMS senses any cell voltages over the limit.
|
10-23-2019, 09:09 PM | #19 |
Getting Wild
Join Date: Sep 2015
Location: Lake Worth, FL
Posts: 76
|
Re: first step in DS conversion to lithium seems easy
I wired up the charging portion of the BMS tonight with a 50.4v 4A charger. All seems to be working well; it has gone from 47.3v to 48.4v when I shut it off for the night.
Below is the technical specs of the BMS from the eBay listing: 12S 150A Li-ion / LiPO Battery protection board. Applicable for 43V (3.6V * 12S) lithium battery & packs 44V (3.7V * 12S) lithium battery & packs 50.4V (4.2V * 12S) lithium battery & packs Lithium battery (Li-ion) Prismatic Lithium Polymer battery (Li-Po) Technical Parameters: Balanced current: 60mA (VCELL = 3.90V when) Balanced for: 4.20 ± 0.05 V Over-charged Protection: 4.2 ± 0.05 V Over-charged Release: 4.05 ± 0.05 V Over-discharged Protection: 2.9 ± 0.05 V Over-charged delay: 5mS Over-current Protecton: 150 A Supports Max. Continuing Discharge Current: 150A Max Charge Current : 40A Static power consumption: less than 200uA Short-circuit protection function: disconnect the load from the recovery. Dimension: 200mm * 110mm * 20mm (L*W*T) - with Radiating Board The main functions: Over-charged, Over-discharged protection, short circuit protection, over-current protection, with Balancing function. |
10-24-2019, 05:51 AM | #20 | ||
Gone Wild
Join Date: Jul 2018
Location: Central Ohio
Posts: 1,720
|
Re: first step in DS conversion to lithium seems easy
Looks like you are on your way! Glad Sergio chimed in to educate us all!
Quote:
Quote:
Is your motor and controller stock? If you have an aftermarket controller you could set it to limit the available amps for these scenarios. |
||
|
|
Similar Threads | ||||
Thread | Forum | |||
Easy Lithium Upgrade? | Electric EZGO | |||
Easy Mailster Electric Conversion | Electric golf carts | |||
Relatively Easy 4WD Conversion | Gas Club Car | |||
G2 to G9 conversion --- the easy way. | Gas Yamaha | |||
Is there a website or link or step by step pictures for the HEI conversion | Gas EZGO |