Overkill Solar Review

JaVid

Solar Enthusiast
Joined
Aug 5, 2020
Messages
102
I purchased (2) 100Amp 24V 8S BMS from Overkill solar in January of 2021.

I put them into service the summer of 2021 and they worked flawlessly until very recently where I started to have issues with one of the BMS. I contacted customer support and received some ideas, none of which worked to fix my issue. They then verified my original purchase and sent out a replacement BMS and sent it Priority Mail so that I could receive it quickly. I received my warranty BMS 10 days after originally contacting Overkill with my issue.

Today I installed the replacement BMS and I am back again running at full capacity. I am a penny pincher by nature, but decided to go with Overkill originally because of their warranty and their support documentation. Boy am I glad that I did!

I plan to double my battery capacity this summer and will be purchasing my BMS's from Overkill for sure. Just wanted to pass on my experience to this forum that has been so helpful over the last couple years...
 

Keith C

Ahhh, the sharks have him.
Joined
Dec 2, 2019
Messages
183
Location
Coastal Silicon Valley
Overkill solar:
Found the BMSes I bought from them for 1/2 the $130 elsewhere.

Those BMSes (24V 8S BMS) do only the BSMing well. Their advertised balancing is pathetic taking probably a year or more to balance a battery with ~180Ahr cells.

The balancing is poorly controllable -frankly stoopid beyond belief.

The tech support was there but I found it to be NOT useful, ultimately having to find the answer to how to even turn on the anemic balancing elsewhere because tech support didn't understand the fickle nomenclature either.

The BMSes are well packed and tested to great detail which you likely wouldn't get anywhere else.
 

ejfluhr

Solar Enthusiast
Joined
May 17, 2020
Messages
25
I have been struggling to get balancing working with my Overkill Solar JBD BMS.
Keith C, can you share what you learned?
 

Keith C

Ahhh, the sharks have him.
Joined
Dec 2, 2019
Messages
183
Location
Coastal Silicon Valley
I have been struggling to get balancing working with my Overkill Solar JBD BMS.
Keith C, can you share what you learned?
Ah yes.. Once you are BlueToothed into the BMS you have to hit the three bars in the upper left corner and go to FUNCTIONs.
In there you will see "Balance Enable". That has to be green (slid to the right).

You will also see "Charge Balance". You need to turn that OFFFFFFFFFF to get ballancing to occur when it can do some good, that is, when you're NOT actually charging! It's stoopid nomenclature that's confusing. The BMS balances ONLY when charging above about 400mA unless your turn OFF "Charge Balance". Then it will NOT balance when charging and instead balances when NOT charging.

They should've stated "Charging Balancing" or "Balancing while charging", or more accurately "Balancing only while charging".
They should've also just offered Balancing ON/OFF but it's what it is.

Note the balancing is an anemic 60mA. So to correct 2amp hours would take 33 hours except you can only do it near the top of the charge 3.45V or higher which barely skims the balancing. I've been balancing 3 of my 8 batteries for two months. I estimate it will probably take a year to finish.

Luckily a 5A flying cap balancer showed up in the mail today. Yippy!
 

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
481
I just bought 3 of the JBD ones with one as a spare for far less than 2 Overkill.
 

pierre

Somewhere down South
Joined
Dec 21, 2019
Messages
913
Cell balancing on the JBD bms is a non-event. Add a Heltec 5amp balancer and turn off balancing on the JBD aka Overkill. I run one on a 48v 16 cell battery with a 200A JBD bms and just leave it connected permanently , charge or discharge.
 

Biasjo

Renewable energy user - North Carolina
Joined
Dec 19, 2021
Messages
547
Cell balancing on the JBD bms is a non-event. Add a Heltec 5amp balancer and turn off balancing on the JBD aka Overkill. I run one on a 48v 16 cell battery with a 200A JBD bms and just leave it connected permanently , charge or discharge.
I did that with 2 of my Batteries that have Overkill BMS.
The Heltek works great.
 

Moltensurf

Solar Enthusiast
Joined
Oct 18, 2020
Messages
135
Cell balancing on the JBD bms is a non-event. Add a Heltec 5amp balancer and turn off balancing on the JBD aka Overkill. I run one on a 48v 16 cell battery with a 200A JBD bms and just leave it connected permanently , charge or discharge.
If you turn off cell balancing on the overkill, what purpose does it serve?
 

Moltensurf

Solar Enthusiast
Joined
Oct 18, 2020
Messages
135
It

It still protects the battery from multiple events that could damage it.
I bought the green MPP all in one unit. In the manual it says I need a secondary Over current protector or disconnect device. Doesn’t my overkill BMS account for this. Thank you
It

It still protects the battery from multiple events that could damage it.
 

Dynoman

Solar Enthusiast
Joined
Dec 17, 2020
Messages
129
Location
Michigan
Anybody have a link to this Heltek balancer?

The Heltec 5a active balancer is used in my system with two grade B 271ah 8s 24 VDC Lifepo4 battery banks and it works well.

Here are links to the Heltec 5a active balancer.

For 4s 12VDC Lifepo4:
https://www.amazon.com/Heltec-Equalizer-Balancer-Equalization-Capacitor/dp/B08CKPZ7PH

For 8s 24VDC:
https://www.amazon.com/Heltec-Equalizer-Balancer-Transfer-Capacitor/dp/B08D9D4NGW

For 16s 48VDC:
https://www.amazon.com/Heltec-Capacitor-Equalizer-Balancer-Titanate/dp/B08M62MVHD/ref=sr_1_2

This is how it's used in my system.

There are (run) solder pads on the Heltec active balancer that can be used to turn the balancer on and off with a switch.

My system uses the relay on the Victron Energy BMV 712 battery shunt display wired to the run solder pads to switch on and off the Heltec active balancer.

At voltages above 27.3VDC the Heltec active balancer is switched on and balancing begins. As the voltage continues to increase above 27.3VDC the Solar Charge Controllers in the system are programmed to go into Boost (absorb) charge at 28 to 28.2VDC for 10 minutes. During boost charge mode the Heltec active balancer keeps all cell voltages at less than 3.55VDC as the cells balance. At the end of 10 minutes of boost charge mode all cells are within 30 mv or less. After 10 minutes of boost the SCC's are programmed to go into float mode at 27.4VDC. The cells continue to balance and after a few minutes in float the cells are within 15 mv or less. The SCC's stay in float mode while suppling loads during the day. Toward the end of the day (or if clouds build) when SCC's cannot hold float and the battery voltage goes below 27.2 the active balancer is turned off by the Victron shunt relay.

I found running the Heltec active balancer all the time would throw off the top balance of the cells in the battery banks and the BMS would disconnect due to some cells going over 3.65 volts.

With my two Overkill Solar 8s 24volt 100amp BMS set at 3.65 Cell Voltage Limit this works well for both battery banks that are in parallel configuration.

It is my understanding that a Digital low voltage battery cut-off relay module is able to turn on and off the Heltec active balancer like the Victron 712 BMV shunt relay, but I have not tried it since my system has the Victron BMV 712 shunt. If some tries this battery cut-off relay module please post your results here. It looks like there are 12 & 24 Volt units. Don't know about 48 Volt...

https://www.amazon.com/NOYITO-Voltage-Detection-Protection-Discharge/dp/B07DS33JVJ
 
Last edited:

Dynoman

Solar Enthusiast
Joined
Dec 17, 2020
Messages
129
Location
Michigan
I bought the green MPP all in one unit. In the manual it says I need a secondary Over current protector or disconnect device. Doesn’t my overkill BMS account for this. Thank you

Yes the Overkill Solar BMS will limit the current to the settings programmed into the BMS. For example the Overkill BMS I use is 8s 24volt 100amp. It will limit the current to 100 amps for both charging and discharging.
 

JaVid

Solar Enthusiast
Joined
Aug 5, 2020
Messages
102
I bought the green MPP all in one unit. In the manual it says I need a secondary Over current protector or disconnect device. Doesn’t my overkill BMS account for this. Thank you
I am not an expert at all on MPP AIO unit, but I think it is asking for a fuse or circuit breaker.
 

JaVid

Solar Enthusiast
Joined
Aug 5, 2020
Messages
102
The Heltec 5a active balancer is used in my system with two grade B 271ah 8s 24 VDC Lifepo4 battery banks and it works well.

Here are links to the Heltec 5a active balancer.

For 4s 12VDC Lifepo4:
https://www.amazon.com/Heltec-Equalizer-Balancer-Equalization-Capacitor/dp/B08CKPZ7PH

For 8s 24VDC:
https://www.amazon.com/Heltec-Equalizer-Balancer-Transfer-Capacitor/dp/B08D9D4NGW

For 16s 48VDC:
https://www.amazon.com/Heltec-Capacitor-Equalizer-Balancer-Titanate/dp/B08M62MVHD/ref=sr_1_2

This is how it's used in my system.

There are (run) solder pads on the Heltec active balancer that can be used to turn the balancer on and off with a switch.

My system uses the relay on the Victron Energy BMV 712 battery shunt display wired to the run solder pads to switch on and off the Heltec active balancer.

At voltages above 27.3VDC the Heltec active balancer is switched on and balancing begins. As the voltage continues to increase above 27.3VDC the Solar Charge Controllers in the system are programmed to go into Boost (absorb) charge at 28 to 28.2VDC for 10 minutes. During boost charge mode the Heltec active balancer keeps all cell voltages at less than 3.55VDC as the cells balance. At the end of 10 minutes of boost charge mode all cells are within 30 mv or less. After 10 minutes of boost the SCC's are programmed to go into float mode at 27.4VDC. The cells continue to balance and after a few minutes in float the cells are within 15 mv or less. The SCC's stay in float mode while suppling loads during the day. Toward the end of the day (or if clouds build) when SCC's cannot hold float and the battery voltage goes below 27.2 the active balancer is turned off by the Victron shunt relay.

I found running the Heltec active balancer all the time would throw off the top balance of the cells in the battery banks and the BMS would disconnect due to some cells going over 3.65 volts.

With my two Overkill Solar 8s 24volt 100amp BMS set at 3.65 Cell Voltage Limit this works well for both battery banks that are in parallel configuration.

It is my understanding that a Digital low voltage battery cut-off relay module is able to turn on and off the Heltec active balancer like the Victron 712 BMV shunt relay, but I have not tried it since my system has the Victron BMV 712 shunt. If some tries this battery cut-off relay module please post your results here. It looks like there are 12 & 24 Volt units. Don't know about 48 Volt...

https://www.amazon.com/NOYITO-Voltage-Detection-Protection-Discharge/dp/B07DS33JVJ
Awesome post and great info. Thank you so much for the in-depth description of how you use the balancer!
 

ncsolarelectric

Engineering Support CEO
Joined
May 24, 2022
Messages
443
Location
Statesville NC
Yes the Overkill Solar BMS will limit the current to the settings programmed into the BMS. For example the Overkill BMS I use is 8s 24volt 100amp. It will limit the current to 100 amps for both charging and discharging.
No, per code the BMS cannot be your Overcurrent Protection for the inverter. Yes, the BMS will limit the current and can even open the circuit, but that is not the OCP that NEC is referring to. A BMS will not qualify as the OCP for the inverter. In some cases the BMS could fail too due to a high surge or short ckt of the battery bank. So no, you MUST have a fuse/CB between the battery bank and the inverter, per code, and for your own safety.
We are discussing a wire-fire in another thread, where the user didn't have a fuse and was relying on the breakers in the multiple battery packs to protect the main line. It didn't. The inverter failed and the BMS (or something) limited the current to a value that just kept re-igniting the wire insulation, but nothing tripped. Had there been a fuse/CB between the battery and the inverter, it would've protected those wires and prevented a fire. Luckily no one was injured.
 
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