MasterShunt on Start Battery

[sailjumanji]

Is anyone using a MasterShunt on their start battery, as part of a Masterbus system?

We are in the process of converting from AGM house batteries to a Mastervolt MLI Ultra (Li Ion). Our complete system is currently Mastervolt/BEP, with all of the charge equipment on a Masterbus system. The AGM house bank is currently monitored by a MasterShunt 500, but the MLI Ultra has its own monitoring functions that will make the MasterShunt redundant.

The start battery will remain AGM, and was thinking of moving the MasterShunt to that side to monitor it. We have dual outboard motors charging directly to the AGM start battery, and a Mac Plus DC-to-DC charger moves current from it to the MLI Ultra with a Li Ion charge profile. At anchor or at dock, another Mac Plus can move current from the MLI to the AGM start battery, to charge it or keep it on float. Anyway, for those reasons, I was thinking that the MasterShunt on the start battery would be beneficial. And besides, I already own it!

I suspect on the Masterbus network, it would just show up as another piece of equipment. Typically the MasterShunt is a power supply for the network, but that will be served by the MLI Ultra. But I see that the MasterShunt power function can be switched off. And we are running MasterAdjust software via a network interface, so everything is easily adjustable (rather than klunking thru the Easy View display).

Anyway, anyone familiar enough with Mastervolt to answer this question, or running a Masterbus system with two MasterShunts, or an MLI Ultra and a MasterShunt on start battery?

[CharlieJ]

Why would you want to monitor the start battery if all it does is start the propulsion engine? Starting an engine literally takes almost no A-hr.

Here is an exercise that I use with my clients:

• 1000A to crank the engine
• Engine starts after 3.6 seconds
• How many amp-hrs are used?

1000A x 3.6 sec x 1 hr/3,600 sec = 1Ahr.

It will take 1Ahr to start this example engine. Therefore, I see no need to monitor Ahr consumption on starting batteries.

[Frankly]

Don't see any advantage to monitoring the starting current. On a more practical consideration there may be multiple battery return paths depending on how the high amperage circuits/equipments are configured. The most obvious is the alternator return and the starter return. If they are connected on the engine end (as typical) then they are likely to both carry starting current (save some unusual battery configuration).

I decided to just use a single large common between the battery return bus and the engine block, so my starting current flows through my shunt (ancient emeter). Starting my 3GM doesn't seem to cause any problems. YMMV.


Frankly

[smac999]

he already has the part. so why not use it. I imagine you can put as many shunts as you want in. you'll just have to name them in the configuration. so you know which one you are displaying. you'll probably need the masteradjust software and usb gateway to set them up. but you probably have already?

if I already had it I would certainly use it.

[sailjumanji]

Why would I want to monitor the start battery? OMG, that's not what I asked. But to humor you, we have failed two Mastervolt AGM's so far. What I know from them is that they like to be fully charged on a weekly basis. So, I have a MasterShunt that is very accurate on SOC, so why not use it.

Reason #2. We have twin outboards. We are running full current to the start battery, and then have a DC to DC charger to run that excess to the house Li Ion battery. It would be really nice to know what "excess" my outboard motors are putting out, other than running around with a clamp meter. Because I can adjust the current limit, via the MasterAdjust software. And with it on the Masterbus system, I log readings at whatever interval I chose. The key to getting everything set up properly is information, and having the MasterShunt and MasterAdjust (DataLogger) logging info certainly helps.

As someone pointed out, I already own the MasterShunt. My concern is that other pieces of equipment can tie into the MasterShunt, and the Li Ion battery BMS, but I don't know if having both in the system will confuse or limit choices. Plus, the MasterShunt is a powering device for the Masterbus, as is the Li Ion battery is a powering device as well. Both will be at different voltages - since the Li Ion house battery will not be same voltage as the start AGM. I am not sure if this causes a problem. I can turn off powering for the MasterShunt though, if that makes a difference.

Which is why I asked for input from someone doing this. And is it really such a bad thing to know SOC of both of your battery banks? We are a sailboat. We really motor very little. We spend time at anchor, we start motors to get off anchor, raise the sails, then motor goes off. It would be nice to know if I need to turn on the DC to DC charger to top off the start battery with the house bank.

Again, my whole issue is not whether it is critical or not. It's whether it is incompatible if the Li Ion BMS is reporting voltages, etc. I have read all of the Mac Plus manual, and the Li Ion manual, and looked at the Mastervolt website, and can find no reference to anyone using separate MasterShunts on the house and start battery bank, or a Li Ion BMS and a MasterShunt on start battery.

[sailjumanji]

We can close this thread. Mastervolt tech says multiple MasterShunts can be installed in the single Masterbus network. (Albeit, I only want to install one.)