Hello, how you doing? Thanks very much for watching. Tomorrow here in the United Kingdom
is a bank holiday but you wouldn't think it. Because the sheer mention of a holiday here,
and it usually throws it down with rain.
But for the last couple of days we've been baking in fantastic sun, all day long and
every morning, I've been waking up to my lithium batteries 100% full, which is fantastic.
But of course, every day isn't as sunny as this. So another way of charging your lithium
batteries, or lead acid batteries or AGM batteries or whatever you have on a narrowboat, is with
an alternator, and that's what today's episode is all about.
The engine on my narrowboat has two alternators. A 75 amp for the starter battery and bow thruster
and a larger 175 amp for the leisure batteries.
In my engine bay is the original large wooden box to contain up to 5 batteries. As I have
my new lithium's inside, in a kitchen cupboard, I wanted to sort the jumble of wires out and
reduce the size of the box.
After removing all the cables, switches and relays I dismantled the grey box and disposed
of it. I cut a new piece of plywood to fit the two brackets that were welded into the
engine bay.
I decided to use two plastic battery boxes with lids. This will keep the
batteries and their terminals clean and give me a lot more space to work with.
Both batteries go through mega fuses and isolator switches. The negative from the alternator
protect battery goes through a Victron BMV 712 battery monitor shunt before joining to
to the main negative bus bar. I've protected both the shunt and the bus bar with Blue Sea
MaxiBus Insulating Covers.
The negative for both alternators is the engine itself. The engine and the negative bus bar
are connected to the steel hull via one connection. Unlike a vehicle, it's highly recommended
to not use the hull as the return negative. All the items onboard should, on a new install,
use two wires, positive flow and negative return.
The 175 amp alternator has two feeds from its positive connection. One goes to the isolation
switch for the alternator protect battery. The other along with a negative from the bus
bar are protected in plastic corrugated conduit, through the bulkhead and into my lithium cupboard.
The positive connects to a fuse on the bus bar.
Alternators, although regulated to a certain degree can treat lithium batteries a little
harshly. Lithium's can take a much higher charge current and for longer and that has
an effect on the alternator.
The recommended charge amperage for each of my 100 amp hour batteries is at, or below 50
amps. Although you can throw 300 amps at them and they will charge, I wanted to look after
my new lithium batteries as well as my alternator.
After a lot of testing I've decided to use a Victron BMS 12/200. It's normally used as
a battery management system but after a bit of digging I discovered this PDF document.
With the use of the Alternator control cable, it ignores the battery management system part
of the unit and instead performs two key functions that I was looking for.
I can regulate the charge current from the alternator with the value of a mega fuse.
The charge value is around 80% of the fuses value and I can go as low as 40 amps and as
high as 200 amps.
I can also use the BMS 12/200 to cut the alternator charge source, just like the battery protect
can for the solar MPPT controller.
The negative from the engine bay connects to the far left
terminal of the BMS 12/200. It goes via the fuse and there is a short length of 50mm cable
from the middle post to the negative of the lithium bus bar. The Alternator cable connects
to both a spade connection on the BMS 12/200 and a three pin plug. The BMS 12/200 requires
a constant positive and switched positive fed from the main lithium Battery Management
System.
If you suddenly cut the load whilst an alternator is running, for example if the batteries were
full, it can damage the alternator. So to avoid this I have used one of my previous
lead acid batteries as a bit of a power dump protector. I will need to have a small load
on this lead acid battery however, otherwise it won't provide that dump load protection,
if it's totally full all the time.
Before the BMS 12/200 was installed, at tick-over I would see around 130-160 amps being pushed into
the batteries constantly, until they were totally full.
The time my 300Ah of batteries took to charge from 50% to 100% was 75 minutes.
After testing the BMS 12/200 with a 150 amp, a 175 amp and a 200 amp fuse, I decided to
stick with the maximum of 200 amps. This reduced the load on the alternator and you could hardly
feel any difference when it was in load and it worked fine at tick over.
The amps gradually reduced over the duration of the charge, protecting the batteries and reducing
the chance of overheating the alternator.
The time my 300 amp hours of batteries took to charge from 50% to 100% with the BMS 12/200
and a 200 amp fuse was 88 minutes.
Although this is slightly slower, I've added the ability to cut the charge automatically
as well as reducing the charge current over the course of the charge.
The values set within the lithium BMS, to me, seemed extreme and you can't change them.
The lithium BMS has a fixed over voltage cut off of 4.2 volts in any one cell.
It has a fixed under voltage cut off of 2.5 volts in any one cell.
However, I already have the kit to tackle this.
In my true belt and braces approach, I wanted to change these voltages. I knew all it would
take for the charge or load to be cut, is the disconnection of their positive feeds. This
would cut both the solar MPPT and the alternator in the event of high voltage and the load
if the voltage got too low.
The BMV 712 battery monitors are already installed measuring the amps in and out, the voltages
and the percentage left in the battery bank. Inside the battery monitor is a small relay.
So I wired the positive feed from the lithium BMS, via the relay.
It's recommended the Victron lithium batteries reach 14.2 volts during their charge so the
batteries internal circuitry can balance the cells.
Within the settings area of the BMV 712 there is a relay tab.
I changed the relay to charger mode, inverted the relay, set the Relay-off delay to 3 minutes
and then set the High voltage relay to disconnect the relay when it's at 14.3 volts.
After a bit of tweaking, the batteries reach 14.3 volts for 3 minutes and then the charge
sources are turned off. No high cell voltages of 4.2 volts!
Now to deal with the low voltage. I already have a second BMV battery monitor [Thought I'd give you a rest from non stop batteries!]
connected to the alternator protect lead acid battery. The monitor has the ability to monitor [Thought I'd give you a rest from non stop batteries!]
an auxiliary or starter battery. So I've wired this connection to the bus bar of the main
lithium bank.
Once again in the settings I changed the relay to charger mode, inverted the relay, set the
Relay-off delay to 3 minutes and then set the starter voltage relay to disconnect
the relay when it's at 2.9 volts.
The relay of this second battery monitor disconnects the load positive feed from the lithium BMS.
This doesn't deal with the MultiPlus Inverter however so I need to look into a way of automatically
disconnecting that too. However the low voltage will be a very, very rare event as I don't
let my batteries get below 50% to increase their lifespan, plus there's always a little
bit of charge from my solar panels, even if it's a horrible winters day.
I am now confident not only are my lithium batteries treated better whilst charging, but
I have introduced a more conservative voltage protection.
I've included links to all the items I've discussed in this episode in the description
below.
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Until next time, see ya later.