We have an older Hatteras yacht with a 32v electrical system. There are two banks of 4ea 8v batteries. Each bank serves as a starting bank for the 12-cylinder engine on that side of the boat. Additionally, one of the banks serves as the “house” bank for DC loads. All charging is handled via a Sterling Power AC to DC charger.
I would like to install a shunt on the bank that handles house loads, but I’m unsure how to do the since it also handles starting the engine, which is in the neighborhood of 1000A when it happens. I see the Lynx system has a 1000A fuse…would that be a good starting place?
Hi @adt2
If you’re talking just a Shunt (rather than a ‘bms’), then many of the Victron shunts come with a range of Amp choices. An example… https://www.victronenergy.com/upload/documents/Datasheet-SmartShunt-EN1.pdf
The Lynx unit is really designed to fit within the Lynx wiring system, and may not suit what you want to do. See the full range on the Victron website.
Look under Battery Monitors, but they can be set up as plain meters too.
If you want to monitor currents only for the house loads section, then install the shunt only “towards” that part of the circuit, without including the starter after it. The starter will take its negative directly from the battery - and before the shunt - as it is now.
Actually, on both sides, the batteries connect directly to an ancient dual battery switch and then run to the starters and other loads. It’s kind of a big scary looking piece of kit, and even when the switches are off there’s still a few things that get DC power - which is one of the things I’m trying to decipher.
I assume the easiest solution is to install a new switch and shunt between the batteries and the existing switch gear, but I’m not sure how I’d break out the starter functionality.
The shunt needs to be directly between the battery and the busbar.
Otherwise the shunt won’t “see” the current that the engine needs to start and also not the energy that’s coming from the alternator (if there is one).
Alex is correct. I don’t really think I need to monitor the engine starters, but I would like to monitor everything else. Unfortunately, the way my boat is set up, each battery bank serves an engine and house loads. So I need an effective way to separate the two functions.
On your proposed V2 diagram is the green box the starter motor. If so, that will only measure current flowing to the house bank. Do you just want to measure the current or do you want it to act as a battery monitor measuring SOC. If you want to measure SOC then your charger needs to connect to the load side of the shunt, not the battery side. Ignoring the Ah used by the starter is probably OK unless you end up doing a lot of cranking one day.
I’m not exactly sure what I want to measure, lol. Right now, I’m measuring nothing. I have no idea what the battery condition is until I either try to start the motor(s), or something onboard that was working suddenly stops working (i.e. lights, toilet flush, bilge pump, etc).
Currently my biggest concern is that I have something (or things) drawing power even when the existing battery switches are turned off, and I would like to both measure the usage and start to modernize our systems (that’s the reason for wanting the shunt). Would also like to know 100% for sure there’s nothing drawing power when the switch is off, which is the reason for the new battery switch ahead of the existing switch.
But I don’t really need to measure anything with respect to the starters, other than just out of curiosity. I assume they don’t draw anything unless they’re being turned over.
If your initial goal is debugging the system it may be easiest to use a SmartShunt set as a DC energy meter, type DC system and measure currents. Then at some point you could reprogram it as a Battery Monitor as you get the wiring under control.
Depending how your engine is wired your panels, engine ancillaries etc. may also come off via the starter.
In your diagram the shunt will see a very high engine starting current, possibly damaging the monitoring equipment. Is it possible to isolate just the alternator output and add a second shunt for the house bank?
Thank you Ludo,
I think I will try installing the shunt on the positive wire coming out of the alternator and just buy a millivolt meter to measure the voltage drop across the shunt then convert the scale to read the output current. I hope it will work.
Mauro
Thank you again Ludo,
Can you comment on my previous proposal to insert the shunt on the positive of the alternator?
I would like to understand this issue a bit better.
