VSDR Lithium Controller Q&A
The VSDR Lithium Controller is discussed in detail in this post – VSDR Lithium Controller – but I get some common questions on it so I thought it would be worth having a specific Question and Answer/FAQ post on its own to help folk understand some of the principles and operation.
Please Note: The content here is provided as general advice and information and is not specific to YOU or YOUR vehicle.
It should be used at your risk, is not warranted or guaranteed in any way and we are not liable for any losses or damage that might occur.
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Common Questions
Q. What Voltage does the VSDR run at? have you a 48V version?
A. We can supply a 12V or 24V VSDR. There are no plans to release a 48V version.
Q. Does the VSDR do any voltage conversion?
A. No. The VSDR operates on the same nominal voltage on both sides e.g. 12V OR 24V, and not a mix.
Q. The VSDR is just a relay, isn’t it?
A. VSDR stands for “Voltage Sending Disconnect Relay”, so yes it is a Relay. But it is a relay whose operation is controlled by highly accurate microprocessor controlled and programmable circuitry. The settings are tuned carefully to work with LiFePO4 Lithium Batteries and their distinct operating parameters.
Q. LiFePo4? Can’t I use any other Lithium-Ion batteries?
A. The VSDRs parameters are setup for LiFePO4 (aka LFP). We do not recommend or support any other type of Lithium Battery technology with the VSDR Lithium Controller.
Q. I see you have a bunch of Victron Monitors. Do I need to have these as well to use the VSDR?
A. No, absolutely not. I have the Victron BMVs so I can monitor the performance of the Hybrid bank to check it is doing exactly what I expect it to be doing. I did this so you don’t have to! They are purely monitors and do not control the working of the VSDR unit. The VSDR is a fully-standalone unit and does not require any external control.
Q. So I need nothing else than your VSDR if I want to add Lithium to a Lead Bank?
A. You do need a way to monitor the Lithium Batteries State of Charge (SOC), but this is no different a situation than if you were switching over from Lead to Lithium. Many Lithium batteries now have internal BMSes that include a SOC Monitor, or you could add a device like a Victron BMV or Smartshunt that will perform that role.
Q. Lead and Lithium run at different voltages. What about power surges when the VSDR connects and they are different?
A. There could be a ‘surge’ of power, but bearing in mind batteries are there to provide power surges I don’t see this as an issue. Take the fitting of a Victron 12/3000 Multiplus inverter/charger, a very popular device. When its inverter kicks in, there is a surge of power pulled from the battery which could exceed 200A. When the charger comes on, there is upto a 120A current going into the battery. Are these power surges in OR out a problem for the battery?
Also, note the voltage differential is actually very small on reconnection in normal operations – the Lithium will be at 13.2-13.3V and the VSDR reconnects when the Lead/Habitation side is at 13.41V, so less than 0.2V differential and the realistic ‘surge’ experienced is tiny.
Q. Do I need a different charger with a Lithium Profile?
A. No. This is actually one of the great things about the Hybrid System when running a VSDR. The VSDR disconnects the Lithium from the Charging System (which is on the Lead side) when the voltage hits a pre-determined value. That value happens to be at the point where the Lithium is between 99-100% full. This prevents the Lithium from receiving a higher Charge voltage (which is what Lead needs) or sitting with a Float Voltage (which is what Lead likes but Lithium does not).
Q. So my existing charger is good?
A. In terms of charging profiles, sure, as long as it can reach over 14.2V Charge Voltage. You might need to consider if it has the ‘oommph’ to charge a larger capacity battery bank, but that would be the same consideration if you were just switching to Lithium 100%.
Q. Because Lithium and Lead sit at different voltages, doesn’t the Lead end up sucking all the energy out the Lithium?
A. This is an interesting point and a common question. Lithium sits at around 13.2V; Lead sits at around 12.7V when full but actually (unlike Lithium) actually prefers to have a bit of a float voltage on it. So the mere fact that the Lithium is causing the Lead to sit at a higher voltage is a win for the Lead and its service life.
If the Lead is in reasonable condition, the actual current going between the two is minimal and even of that minimal current only a small percentage is actually ‘lost’.
Q. Other devices used on a Hybrid Bank seem much more complex and ‘featured’. Why is yours just a relay?
A. I cannot speak for the alternative options that may be available. The VSDR was developed to serve a very specific purpose – that being a highly controlled disconnect and reconnection of two dissimilar battery technologies – and I believe it performs that role very well and precisely as expected.