This is about destructive BMS disconnects in lithium battery systems with high powered alternators.
I understand the concept of “load dumps”: If you are charging a lithium bank at high amperage with an alternator, and the BMS of the lithium battery decides to disconnect it for safety reasons (for example, overtemp or overvoltage), you can get huge voltage spikes up to 10x bus voltage which can fry your electronics, because the alternator controller cannot react quickly enough to lower the output.
The solution is to have the battery BMS communicate to the alternator controller to stop alternator charging before BMS disconnects the battery. Wakespeed, who makes a popular smart alternator controller, specifically talks about support for communication over CAN to mitigate load dumps. I’ve had trouble figuring out what communication protocol is required, and therefore having trouble figuring out what batteries support the necessary communication.
I also know that DVCC is a Victron technology that manages charge rates for the multiple chargers based on BMS demand, and know that DVCC works with Wakespeed alternator controllers. So the key question is whether DVCC support in a battery is enough to ensure the system will be safe from load dumps.
Specific questions:
Is DVCC support sufficient to support safe disconnect (and mitigating load dumps)?
If more than DVCC is required, what is the name of the message/bus/protocol the BMS must support? (in other words, what do I need to ask battery companies for in terms of support)
What battery brands have the support necessary to communicate this safe disconnect message to alt controllers?
3a) Epoch makes a “victron compatible” battery with CAN comms. Is this communication enough to mitigate load dumps from a Wakespeed WS500?
Any knowledge on how alternator load dumps are protected via CAN comms, using DVCC or other, would be greatly appreciated.
Details: System will have Cerbo GX to manage DVCC, and will have 3 sources of charging: Multiplus-II, Blue solar MPPT, Wakespeed WS500. My goal is to figure out what battery BMS will be compatible to preventing load dumps.
2 wire signals - allow-to-charge and allow-to-discharge
Victron smart lithium and smart lithium NG with suitable Victron BMS. Lithionics also supports this with their external BMS. Maybe other brands but these are the ones I’m familiar with
3a. No, and the BMS in their batteries is not great and have limitations with charge voltages and cell voltage overshoot
It’s not sufficient in my book and I would only install it as extra insurance with a proper external regulator AND battery BMS with ATC & ATD control lines
If you are in the USA, consider the Zeus regulator and Zeus alternator instead of a Wakespeed and other alternator. The Wakespeed was great when it was the primary solution on the market, but the introduction of the Zeus over a year ago provides a better solution in my opinion.
@gtg356y
Further to Ed’s post covering everything, the Victron Lynx BMS can be set up to shut down a Wakespeed or Zeus or similar 2 seconds before it opens the contactor.
Thank you Ed! You’ve provided more information in this response than any of the technical support personnel from battery and alternator companies I’ve spoken to.
One told me this communication was done over CAN, but now I see that it is a dedicated ATC wire coming from the BMS to the alt controller–and I see it in the Zeus and Lynx BMS pinouts.
What’s surprising to me is how limited this support seems to be, and how little it is advertised. If only a couple batteries and alt controllers support this, is it simply the case that most builders are just ignoring this issue, and not designing for it in their builds? Is it just extremely rare that the BMS disconnects while charging?
@gtg356y Hello, I cannot provide a lot of specific information you are requesting but can provide some food for thought. I wonder are you developing a product or delving into this subject simply for your own use?
If the Wakespeed external regulator is controlled by DVCC, the Charge Curerent Limit (CCL) needs to be advised by the battery bank to limit the charge current as the battery approaches the point where it goes into “Protection Mode” and disconnects. When CCL is lowered all charging sources (Including the regulated alternator) reduce charging current to suit. Any battery that provides a CCL and actually manages that CCL so it reduces the CCL prior to a disconnection event will satiisfy this need.
@Trevor,
Yes ATC can provide protection if properly managed by the BMS, But so does Can communication if the BMS is properly designed.
Load dump happens if the BMS opens the contactor before shutting down the alternator. Dvcc by itself does not.
Some BMS like the MG energy systems Battery BMS directly controls the regulator, or more specifically the regulator directly listens to the BMS and does not respond to dvcc.
That is the case of the Wakespeed and the Zeus regulators.
The ATC signal is being sent via the canbus network. The regulator listens to that signal to turn the field ON or OFF. The MG BMS ensure that the ATC signal is off way before it opens the contactors. Should the regulator loose communication, they will automatically go to standby and shutdown the field.
In short Load Dump protection can be done via canbus if the BMS is properly designed. In the case. MG energy Batteries would be compatible with your system.
Whether the ATC is hard wired or networked, your system will not be protected from uncontrolled system stops like a fuse blow. Only active overvoltage protection can avoid those issues.
They are field regulators that have built-in load dump protections. Specifically MG field regulator AFC300 and Scotty DcDc alternator regulators from Safiery. Those regulators have builtin overvoltage protection that are designed to absorb the load dump energy of the regulator should something external like a fuse blow cause the DC circuit to be interrupted.
Thanks. I’m somewhat confused by your statement on DVCC support. You said Wakespeed and Zeus “do not respond to DVCC.” I assume you mean that the ATC line will override DVCC if a "stop charging is commanded?
Also, regarding CAN vs wired comms ATC communication. I see BMSs like the Lynx BMS, as well as regulators like Zeus and Wakespeed, have both CAN comms as well as dedicated ATC wires. Are you saying the ATC wire is optional if you are connecting over CAN, because they send the message over the CANbus? How do I know which systems are compatible with the networked communication versus the wired?
The direct response to the thread question is NO. DVCC does not protect an alternator from load Dump. This is re responsibility of the BMS.
Only way to protect from Load dump is to turn off the field before disconnecting the main power to/from the alternator. The BMS generates the ATC signal. Whether connected to the Ignition wire of a regulator or properly managed via the canbus network, a properly designed BMS will ensure that function.
The solution highlighted in the thread suggest that you always have to use a wired ATC signal. In the case of the MG Energy Systems this is not required. The regulators are listening to the BMS, not to the GX device/DVCC. The BMS will always disable the charge via canbus prior to opening the main contactor. This may not be the case for other batteries including the Victron smart batteries.
To my knowledge, DVCC function in the GX does not control external regulators or loads unless they are externally measured by a DC meter. It simply controls a VE.BUS device and MPPT’s. It does not even regulate a Victron Skylla devices. Refer to GX documentation (11.4.1.3). DVCC generates 3 numbers CVL/CCL/DCL. It does not appear to directly generate an ATC/ATD signals.
For this you have to specifically asked the regulator or the Battery manufacturer for their recommendations. They are no simple answers.
The Zeus and Wakespeed are fully integrated into DVCC control and get target voltage and or current from the GX device. They do need their own alternator current shunt in place for this.
My understanding is aligned with you, pwfarnell. I thought that Wakespeed and Zeus ARE compatible with the “charge control limit” of DVCC which means that they will reduce their current output (and thus field) when the CCL is adjusted by the BMS. Here is the firmware page for Zeus that talks about the DVCC support. It clearly indicates it has the ability to follow the charge rates commanded over DVCC, although you need a dedicated alternator shunt in order for the DVCC to measure its contribution to the system.
Jean Marc to your point, Victron’s own documentation seems to contradict what Zeus and Wakespeed appear to support. 11.4.1.2 appears to say that aside from Victron inverters, solar chargers, and DC-DC converters, “Any other sources will be extra charge current, unaccounted for. Even when installing a BMV or other battery monitor.” This is confusing to me.
Assuming though that a BMS can command a CCL, and the Zeus alternator controller is equipped to respond to it, it appears to me that load dump protection COULD be done through DVCC – the BMS would simply command a CCL of 0 a few seconds prior to opening contactors. I don’t know if the implementation of DVCC supports this nor if the BMS software would use this.