question

solgato avatar image
solgato asked

Integrating Battery Protect BP-65

Researching the BP-65 to see if I can integrate it into my system.


What I want to do is use it between my MPPT 75/15’s and my 24V LifePo4 to interrupt charging in the event of a cell balancing issue (overcharging).


As I understand it can be used to do this although it is more commonly used to interrupt load output power supply to protect against undercharged state.


My question is, how do the contacts work on the BP-65? I see it has a High, Low and Ground.


I was hoping to be able to use an aftermarket BMS to trigger disconnect. It’s contact outputs are open collector types with High Limit Switch, Low Limit Switch, and Ground terminals. It’s configured to be open at all times and then grounds out when activated to trigger an external device.


Does the BP-65 work the same way? Is it a normally open device?


If so, would it be as simple as connecting the HLS output terminal of the aftermarket BMS to the H input terminal of the BP-65 along with Ground to Ground?


I have a BMV-712 and understand I could connect the BP-65 to it to trigger disconnect, but the aftermarket BMS is able to monitor my battery cells individually versus an overall Over Voltage trigger which is how I understand the BMV-712 and the BP-65 work, with 712 monitoring/measuring if there is an overall Over Voltage condition in which case it triggers the BP-65 to disconnect.



Battery Protect
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1 Answer
wkirby avatar image
wkirby answered ·

Regarding the remote input scenarios:
If both H and L terminals are floating, BP is disabled.
If both terminals are connected together, BP is enabled.
If H terminal is pulled high, BP is enabled. A weak pull up is sufficient, 100KΩ will do it.
If L terminal is pulled low, BP is enabled.

So, with open collector output on your BMS, you'll need to add a weak pull up resistor to pull the H terminal high and then the BMS open collector can pull the H terminal low to disable charging.

Are you using the MPPT's VE.Direct port for anything? If not, you could disable the MPPT with a signal on the Rx pin.

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solgato avatar image solgato commented ·

Thanks for your response.

Adding the resistor is an easy enough work around.

Regarding the VE.Direct port on the MPPT, are you saying it’s possible to disable charging directly without the need for the BP using the aftermarket BMS High Limit terminal to trigger?

I had inquired about this in another post but didn’t get any responses which made me consider adding the BP.

With the ability to disable and enable the MPPT’s so easily using the App, and the ability for the BMV-712 to remotely control a MPPT, I thought/hoped there would be an easy way to trigger disconnect directly via the open collector outputs of the aftermarket BMV.

If this is the case, how would I go go about making it possible to disable the MPPT with a signal at the Rx pin?

This sounds like a much simpler option without the need for another piece of hardware. Plus with the way I’d be using the BP, it’s nothing more than a fancy relay since I wouldn’t be using any of its intelligence. In fact the open collector outputs of the aftermarket BMS are designed to be used with common automotive relays.


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wkirby avatar image wkirby ♦♦ solgato commented ·

Set the Rx pin function to "Remote On/Off".
Then you can pull the Rx pin down to disable the MPPT, which is rather convenient for your open collector output of your BMS.

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solgato avatar image solgato wkirby ♦♦ commented ·

Thanks again Wkirby. Appreciate the guidance.

It’s unfortunate there’s no way to do the same thing using my BMV712 at the shunt.

Would be easier because the aftermarket BMS will live in the same hatch as the shunt. My MPPT chargers are many feet away.

I looked into whether it was possible, but see that there isn’t even away to control the Chargers from within the 712’s settings in the App even though it is networked with the MPPT’s and has the ability to trigger their disconnect via programmed limits.

Would be nice if you could Disable all chargers on the network via the 712.

Which brings me to my next question, will there be a problem if I try to control two chargers using the open collector output of the aftermarket BMS?

My chargers are in parallel to my bank, so I need to trigger on/off of both remotely in the case of a cell inbalance.

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