More than One Shunt

[Mark Johnson]

I am a firm believer in simplification. What we did is:

Install a large house bank, (>10 year lifespan)... and a very small $60 engine battery, which is not meant to last but a few years.

We have two three way selector switches. One selects which bank to crank the engine with, and the other selects which bank to run the boat on. Both switches have been used in the same positions for 15 years. (Eng. bat. switch to the eng, and house bat. switch to run the "house"). They were only installed as "worst case" options, and we've never needed them.

The solar panels, dockside charger, and alternator, ALL GO TO THE HOUSE BANK... ONLY!

(Yes, the alternator should ideally have it's neg. wire go directly to the alternator, AND have a "Zap Stop".) This is as opposed to just any engine bolt.

The house bank is paralleled to the eng. battery with a "blue Sea" battery combiner. With this, the engine battery gets the few amps that it needs after cranking the engine, from the alternator bringing the house bank's line v above 13v, then the combiner "combines", and the banks are paralleled. (The eng. battery will be charged in about 15 minutes).

As soon as all charging sources are off, and you are running on the house bank, the line v goes below 13v and the "combiner" disconnects the two banks. This way there is no way to accidentally discharge the engine battery, by running the boat.

You run EVERYTHING on the house bank, and need only one "Link 10" shunt, sensor wires, etc.

Since the engine battery is never really used, except to crank the engine, It is always pretty much full, and a simple v meter should let you know if there is a problem.

With the "Link 10" you know exactly the amps in, amps out, line v, and a/h in or out, of the house bank. This is the only one that requires this much information.

If your house bank went flat, the small engine battery COULD be manually switched to run the boat momentarily, but it makes more sense to me to use that eng. batteries' juice to crank the engine, thereby charging BOTH banks.

It sounds like you are trying to have too many bases covered with redundant capabilities, above and beyond what is likely to be needed, at the expense of simplicity.

To keep your ass covered, have an energy efficient boat, and "house" battery bank that can run it for several days by itself. We only cycle ours down to 95% or 85% FULL, every day, before total recharge. It would take a major brain fart lasting several days, for our house bank to go flat.

These systems are perhaps the most vulnerable on the boat.. simplify! IMO...

Mark

[goboatingnow]

most shunts are either 50mV/A or 100 mV/A usually stamped on the shunt.

If the shunts are the same you can connect both monitors to each shunt. Connecting two in series is perfectly fine, the resistance is tiny.

Dave

[Extemporaneous]

Thanks Guys for both the answers (and the opinions).
Some of it is very helpful!

Cheers,
Extemp.

[DeepFrz]

Connecting the shunts in series isn't a problem, theory wise, however, you are adding several more high current connections plus the extra shunt. If the shunts are the same value, I would recommend, in the interest of simplicity, that you use just one. Keep the other as a spare.

[Extemporaneous]

Originally Posted by DeepFrz

Connecting the shunts in series isn't a problem, theory wise, however, you are adding several more high current connections plus the extra shunt. If the shunts are the same value, I would recommend, in the interest of simplicity, that you use just one. Keep the other as a spare.

Thanks DeepFrz,
Once I get a level of comfort as to how the two monitors work separately, I'll then hook them up as you suggest.

Thanks again,
Extemp.