When I purchased my van back in 2017, it already had lithium which I knew I wanted for my van. The debate could go back and forth about if lithium is worth it or not, but for me, itís what I wanted and bonus, it was in my van when I purchased. However, Iíve always been a little bit disappointed with the BMS as I felt it was lacking in several areas. In this post, Iíll talk about how I addressed those and how someone looking to build their own lithium bank can go about it today. Iím also going to talk about some utterly useless addons that no sane person actually needs. I just like to tinkerÖ.
The lithium in my van is built with raw large prismatic cells with an external BMS that was pieced together at AM solar from different suppliers. The BMS was a Power House Auto Mini BMS v7(sadly itís no longer in production, but there is a GREAT replacement that Iíll talk about later in this post). Itís a very basic BMS with hard limits (you canít program it yourself) but it does the job. It has the ability to turn off chargers when the voltage gets too high (HVC at 3.6v per cell) and turn off loads when the voltage gets too low (LVC at 2.9v per cell). When the voltage recovers (3.1v or 3.5v) the chargers or loads turn back on on its own. Each of these have a 10 seconds warning phase in case of sag or low voltage drop, so if they arenít addressed (IE there is a problem with the BMS or a relay), it also have a main contactor (500amp Tyco EV200) for emergencies in the event the BMS does not shut off the charger or loads (3.65v or 2.6v). When this happens, there is a momentary switch used to signal the alarm and requires you to hit a button to ďresetĒ the battery. This is there to prevent automatic restart and further deplete or overcharge the battery.
As shipped from AM solar, it only had the main contactor to shut off the battery for either a HVC or LVC condition. While Iíve never had either happen, it always bugged me that if there is ever a problem with the balance of the battery or it was over discharged, it will shut off the battery entirely (including chargers). Since I travel with my wife who has asthma, she doesnít go with me on very strenuous or high-altitude hikes. We also take my mother in law sometimes (I get booted to a tent). Iíve always worried about the battery shutting off and one of them not knowing how to reset it.
Since the BMS has the ability to add high and low voltage disconnects, I looked into the BMS more to figure out how to achieve this. I found that the BMS will pull to ground on the low and high voltage ports on the board. This is inverted compared to a typical BMS which will remove the high or low when there is an alarm. It would also make it difficult to find Normally closed relays that could handle a decent amount of current for my chargers. I ended up building out a few relays on top of the BMS to invert the signals. To do this, I used standard automotive relays that have a Normally Open pin and a Normally closed pin. So the common wire is a 12v signal and the output to the disconnect is on the Normally closed pin so when the BMS if fine, itís passing through the 12v signal. Because Iím using the same power to power the relay as the COM, this is no longer an isolated circuit. I found a 4 channel optocoupler which will isolate the circuit for up to 4 signals (this will prove to perfect for my application). Now I have taken the output of the NC relay for the low voltage condition to a splitter (wago connector) to two of the optocouplers and the output of the NC relay for the high voltage condition to another splitter and now I have two outputs for each condition (low voltage and high voltage).
Old BMS in itís small box:
New BMS I wired together with those green phoenix connectors to make install easier:
4 Channel Optoisolator in the old BMS box (recycling and saving money):
So now that I have the outputs on the BMS, I needed to find a solution for turning off my chargers (Charger on the inverter, my charge relay linking the starting battery for charging from the alternator and the MPPT charger) and loads (DC loads and inverter). My inverter was a Magnum MS2000. This inverter has been rock solid since the day I got the van (and I assume the previous owner had no problems with it). The issue with it was the ability to remotely turn off the charger. Magnum has an accessory to turn off the inverter, but did not make one for the charger. I very rarely use shore power at all since I mostly camp at BLM spots, but if I wanted to make a full proof solution, I needed to come up with something. Of all the 12v inverter/chargers on the market, only one has a remote switch to shut off the charger fuction: Victron Multiplus series of inverter/chargers. I ended up getting a great deal on a gently used Multiplus 3000. Itís a bigger unit that I needed, but at the cost, I couldnít pass it up. This would give me to 1 signal from the HVC out to turn off the charger and 1 signal from the LVC output to turn off the inverter.
Iíll be using the two AUX inputs to disabled the charger and inverter with the software assistant:
I also wanted to protect my new inverter. Hooking up an inverter through a contactor will subject both to high inrush currents. Thankfully REC-BMS makes such a device in a small package. It also is time adjustable from 1 second to 11 seconds. The pre-charge unit is a device that charges the input capacitors of the system components before the main contactor switches on. Pre-charge device eliminates high inrush currents at the switch-on of the contactor and prolongs the contactor lifespan dramatically. I tested it on my bench setup before installing:
With the timer switch:
And it fit perfectly where the old BMS box went right next to the contactor:
Next up I wanted to address the charge relay for linking the starting battery to the house battery. It was a Blue Sea ACR. The selling feature of the ACR (other than the 500amp rating) is that auto sensing voltage reading. Basically, when it senses a battery above 13.2v, it thinks one of them is charging so it will link the batteries. The problem with lithium is they have a high resting voltage than lead acid so the ACR will always want to connect the batteries. I never really used the ACR as solar has always kept up with my loads, but itís always nice to have the option. I also wanted to regulate the charge current to my batteries so I opted to go with a DC-DC charger. I ended up with an Australian version of the Kisae DMT-1250. When researching dc-dc chargers, for some reason google didnít show me the Kisae but did point me to an Enerdrive version of the same thing. A quick email to my friend in Sydney and a quick PP gift payment, I had a new one on itís way. When it arrived a few weeks later, I learned of the Kisae model. I paid around the price but paid for shipping from Austraila. Oh well live and learn. This unit is pretty slick as it does 50 amps either from solar or alternator/starting battery. You can have both hooked up so for a smaller install, this could be an all in one DC charger. However since I have a 400ah bank, if I ever was in a jam and need to recharge quickly, I can charge from whatever solar gives me, plus the 50 amps from the alternator.
So now all thatís left are relatively low current items. Victron makes battery protects that can be used as switches. They arenít contactors, but mosfets. The downside to this is current can only flow in one direction plus they canít handle high inrush currents from large inverters (but I already handled the inverter above). What I ended up doing is to have the output of my DC-DC charger and the MPPT charger controller to a battery protect. This effectively shut off the chargers by disconnecting the battery. This presented a problem for my MPPT charger controller. It didnít like having the charger disconnect from the battery (which I knew from a previous change I made to my system a year or so ago). When the battery was present again, in certain circumstances it wouldnít reconnect the charge properly. It also had my battery monitor on the remote panel so if I ever had the BMS disconnect the chargers, it would disconnect the remote panel and the SOC of my battery would reset. I decided it would be best to just replace the MPPT charger AND the battery monitor with two separate units. Since I already had a Victron inverter, I decided to go with a Victron MPPT 100-50 and a BMV-712 battery monitor. The battery monitor is a great unit as you can set charge efficiency and Peukert ratio. This better handles the calculation of state of charge for lithium batteries. I highly recommend the BMV700 series if you want a battery monitor. With the BMV-712, there is also temp probe that you can add and a programable relay (which Iíll get to later in this already super long post).
DC-DC charger along with the new MPPT I also used this time to add some breakers as the old system didnít have any. I also added a two way switch so that if I end up with a dead battery, I could switch to position two and link the starter battery and house battery manually (blurry photo, but itís there):
So now that I had a new mppt that wonít have issues if I remove the battery, I ended up getting a BP100 that can handle 100 amps. My DC-DC charger for my alternator charging is 50 amps and I currently only have 300w of solar on the roof and that max Iíve ever seen from the mppt is 17.8amps so a total of 67.8amps. I took output of each charger to the input of the Battery Protect. Then the output of the battery protect went to my busbar to the battery. I then took the remaining HVC signal and wired that to the Battery Protect. Since the Battery protect is programable, I can program it in Lithium Mode which will take the signal and act as a switch. It also has a 30 second cool up period after the BMS wants to turn the battery back on so the voltage can recover. As for the remain loads, itís just my DC circuits. I took the remaining LVC signal and wired it to a BP65 battery protect. This will disconnect my DC loads in the same way as the BP100 will disconnect my chargers.
Some photos before the BMS hookups. I also remade all my DC cables as they were poorly crimped and undersized in some areas. Iíve also included a screen grab from the BP showing when the BMS disconnects the loads:
So the BMS is almost perfect. The last item to address is low temps and disconnecting the charge sources. I had previously used another Tyco200 (overkill but I had an extra one) and an external 12v thermostat to disconnect the panels from the charge controller. This worked and would have continued to work, but now that I had a Victron Battery Monitor with temp probe and programable relay, what I did was take the HVC signal that disconnect the BP100 and before it went to the BP100, I took it to the BMV712 relay com port, then ran the normally closed output of the BMV to the BP100. This way, if the BMV seems a high or low temp that I can set, it will open the relay and disconnect the chargers. Now because this is only going to the BP100, it wonít turn off the charger on the inverter charger. I almost never use shore power, but if I do Iíll be using the van and keep it heated. Plus Iíve since moved to Nevada, so I donít think Iíll ever be traveling in the van to a place where it will get that cold that quickly where the van wouldnít have heat on. Though now that Iím writing this out, the Multiplus does have extra aux inputs so I could possibly find a way to use one of those input and the normally open port on the BMV to disconnect the charger as wellÖ.hmmmmm An edit may be coming.
Everything is installed and working great. Now that I have pretty much all Victron components, I had thought about adding a Color Control GX (Venus OS) to network all the chargers together. The benefit of this is you can enable a feature called Distributed Voltage and Current Control. This allows you set a max charge current as well as share the temp and voltage of the battery with your other chargers. This basically negates the need for the relay in the BMV as the venus will control the chargers that are networked (Victron chargers). However I still have it setup through the relay of the BMV as the Dc-DC charger isnít Victron. So if you want to max your charge to .5c for the best health of the battery, you can set the limit. If you have a 200ah battery, you can set the max charge to 100 amps. So if you have a multiplus 3000 with a 120 amp charger and you are bringing in 20 amps from solar, it can lower the charge rate or the multiplus to 80amp plus 20 amps from solar (it will always prioritize solar). Solar charge goes down to 10 amps, multiplus goes to 90 amps. Thatís just one of many features it can do. It can log all your production data, send alarms to your email, and much much more. The color control is an expensive product, but Victron software is open source. Someone at Victron ported the OS of the color control to a Rapsberry Pi ($35 all in one computer). I had one laying around and added a $50 touch screen and a $100 mount, a few serial to USB cables and I have a touch screen version of the color control GX. Iíve added a GPS module to the Venus so you can set a geofence. If the van leaves my neighborhood, Iíll get an email about it. I also purchased a cheap 4G/LTE modem and a $50 a year data plan with 1GB of data per month so the van is always sending info from the van. This was the part of the build that was TOTALLY unnecessary. I work in IT, so this was a fun little project that didnít add much to the cost of the upgrades. I also purchased and Analog to Digital converter board for the Pi to take the resistive signal from my auxiliary diesel tank for my heater and input that into the Venus as well so my tank gauge was no longer needed as itís on the Venus OS.