Lithium - how did you do it?

[cheesegas]

Hi all. Got my lithium setup at a place now where it all works well after installing it at the start of the year. There's a whole bunch of different ways to do it, and I'm intrigued as to some different ways to get ideas. Aim was to do it on a budget, whilst avoiding lead times and having total system control relying on the BMS as a last resort protection, not routinely using it to limit charge cutoff.

 

Most of the functions of the Cerbo have a manual hardware override in case it fails. Fairly complex but it's easy enough to troubleshoot. I'm totally off grid, no shore power.

 

All in all, it works very well and with minimal intervention, it just looks after itself and whenever I get a text or the wall controller beeps, it's time to put the engine/genny on. Standby current of the whole boat - toilet fan, cat fountain, 4G router and Cerbo - is about 10 watts. 

 

Kit

House battery - 4 Lifepo4 cells and a JBD/Overkill BMS (£500)

Start battery - lead acid, 18a DC-DC charger (£80 for the DC-DC, kept the original start battery)

Heating - 100w silicone pads and a thermostatic controller (£40)

Engine -  3 pot Isuzu with a single 75a A127 alternator and Balmar ARS5 reg (£30 for the Balmar, £0 to modify the A127 reg)

Inverter/charger - Victron Multiplus (already in place, as were the last 3 items)

Solar - Victron 100/35 MPPT

Battery monitor - Victron BMV

Control - Cerbo GX running the Large OS and Node-Red. Amazon Fire tablet in picture frame showing the Node-Red dashboard.

 

I would have preferred a REC BMS but lead times were over 2 months when I ordered, and it still didn't arrive. I'd also have liked a dual alternator setup to eliminate the possible failure point of the B2B, but I couldn't source a front pulley without having one machined. Next step is to connect the JBD BMS to the Cerbo via RS485 so it appears as a BMV, using the JBD's built in shunt.

 

 

Alternator charging

Alternator output goes to the house bank, as does the Balmar's sense wire. It's set up to regulate to 13.8v with the field percentage set to zero so it basically never tries to go onto the absorb/float stages, just plain 13.8v. Temperature sensor is an LM235H on the alternator's negative terminal.

 

The ignition wire to the Balmar goes to a NO relay; one side of the relay is switched positive by the ignition switch, the other side is grounded by relay 1 on the Cerbo. A node-red script on the Cerbo controls charging - when the BMV reports below 95% SOC and the engine is running (the Cerbo has ignition positive wired to a digital input), it closes relay 1 which engages the alternator. When it gets to 100%, the relay is opened, stopping charge. As the float voltage of the solar controller is set to 13.4v, the battery discharges a little before settling there. The alternator is only engaged again if the SOC drops below 94%.

 

I also have a manual override switch which shorts the neg side of the relay coil to battery neg to force charging if the cerbo fails.

 

However, the A127 alternator will happily charge at 50a at a good temperature. This presents a fair load on the engine; fine at tickover (or just above!) out of gear, but if it's in gear cruising along at tickover whilst charging, the idle speed is pulled down from 950rpm to 600-700rpm. That's right in the lumpy, vibey range for the engine, not nice. I therefore have a limit switch on the throttle and gear linkages, which short circuit the Balmar's temp sensor when in gear and at idle, which limits the charge current to a point which doesn't pull the RPMs down noticeably.

 

There's a 3 position switch on the engine dashboard to turn alternator charging off, limit to slow charging or auto, using the switches above.


Battery heating

The batteries are in a cruiser stern, which dropped below zero in Jan. The cells are insulated, and have two 100w silicone heater pads, one on each side of the pack. These have a built-in 80C cutoff thermostat which is used as a safety. It's controlled by a cheap digital thermostat, set to maintain temp at 50C; much like a fridge, if they were switched on until the thermistor on the battery terminals read above zero, the pads would overheat before their heat is transferred into the mass of the batteries. The thermostat's sensor cycles them on and off nicely.

The thermostat is switched on by relay 2 on the Cerbo, controlled by anothe  Node-Red script. I wanted them to be warm enough to accept a charge as soon as possible; the script turns the heaters on if the Cerbo's temp sensor reads below 2C, AND the PV wattage is over 10w,  AND it's before 10am. Another flow turns the heater on if the engine is running/shore power is available AND it's below 2C. I also have a manual override on the Node-Red dashboard (and a hardware switch) to turn the heaters on, for example if I want to run the engine to charge the batteries and it's too cold.


Solar/Shore
Nothing fancy here, DVCC on the Cerbo shares battery current/voltage/temp with the Multiplus and MPTT which don't charge below 2C.

[nicknorman]

Sounds like you have a pretty comprehensive system. It’s a pity that model of Balmar doesn’t really do “small engine mode” properly, ie automatically reduce max field current at low engine rpm. And you can’t interconnect the Balmar with the Cerbo such that the Balmar can be put into float (so that it continue to supply high loads eg to an inverter) without affecting battery charge. But anyway, nothing is perfect but you seem to have a good compromise at low cost.

[MtB]

What's a Cerbo?

 

[nicknorman]

7 minutes ago, MtB said:

What's a Cerbo?

 

It’s a Victron product that is a sort of data concentrator that allows data from various different devices to be gathered, and outputs switched or whatever, according to a programme. And can interface with Bluetooth, internet etc for remote monitoring.

 

https://www.victronenergy.com/panel-systems-remote-monitoring/cerbo-gx

Edited October 5, 2022 by nicknorman

[cheesegas]

25 minutes ago, MtB said:

What's a Cerbo?

As above, it’s basically a tiny computer which connects to all Victron and some non-Victron products to provide control over them, and output a customisable display. You can also do handy stuff like have one temperature sensor and one voltage meter which is shared amongst all inverters/MPPTs etc on the network. 
 

It also sends data to Victrons VRM portal for free, so you can log in anywhere in the world and see your electrical systems data like state of charge, and also GPS location. I’ve attached what mine looks like currently. 
 

There’s an active community of people who modify the codebase and interface as Victron have made it partially open source, it’s very customisable. The software it runs can also be installed on a Raspberry Pi (low cost mini computer) for similar functionality. 
 

I’m a big fan basically. Expensive hardware but the software is made very easy thanks to Victron. 

41 minutes ago, nicknorman said:

Sounds like you have a pretty comprehensive system. It’s a pity that model of Balmar doesn’t really do “small engine mode” properly, ie automatically reduce max field current at low engine rpm. And you can’t interconnect the Balmar with the Cerbo such that the Balmar can be put into float (so that it continue to supply high loads eg to an inverter) without affecting battery charge. But anyway, nothing is perfect but you seem to have a good compromise at low cost.

Yep, that’s the one thing I’d like, as a high load will result in the battery cycling from 95-100% which isn’t good for it. Unfortunately only the Wakespeed or Mastervolt controllers will allow it…if I see one for cheap I might get it. 
 

And yeah, since the balmar knows the engine RPM thanks to the tacho input, it’s a shame it can’t be done automatically.