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Old 17-11-2014, 03:49   #1
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A Question for Electrical Geniuses

I would like to measure DC current into and out of my batteries. But my battery bank is divided into two parts (4x Trojans in each) in two different locations. So there is no single cable which carries all the current.

So I need some kind of totalizer -- some instrument which can add the current from shunts or inductive sensors on two different cables and display the total.

Does such a thing exist?
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Old 17-11-2014, 06:34   #2
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Re: A Question for Electrical Geniuses

There isn't a single cable coming out of the charging source? How do these banks supply distributed power? Is there a common point at the panel? These banks should be tied together with a common ground.

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Old 17-11-2014, 06:45   #3
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Re: A Question for Electrical Geniuses

Quote:
Originally Posted by Dockhead View Post
I would like to measure DC current into and out of my batteries. But my battery bank is divided into two parts (4x Trojans in each) in two different locations. So there is no single cable which carries all the current.

So I need some kind of totalizer -- some instrument which can add the current from shunts or inductive sensors on two different cables and display the total.

Does such a thing exist?
I have looked for a low cost -+ammeter/totalizer and could not find anything inexpensive.

I ended up buying the BMV700 series monitor.

It is designed to measure the amps in and out of the primary bank and provide voltage on primary and secondary.

You could install this monitor (shunt) between the 1-2-all switch and the DC bus. Then it would be measuring the amps in or out of whatever bank is connected.

You would ignore the SOC feature but I think it would do what you want.

All charging sources would need to be downstream of the shunt (i.e. on the DC bus) to measure amps in.
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Old 17-11-2014, 07:03   #4
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Re: A Question for Electrical Geniuses

Yeah just install the shunt in series with the battery switch. A meter there will measure total current, whether you are on bank A, B, or both.

You can also meter each bank seperately. Simply add the currents to get total current.
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Old 17-11-2014, 07:54   #5
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Re: A Question for Electrical Geniuses

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Originally Posted by Dockhead View Post
I would like to measure DC current into and out of my batteries. But my battery bank is divided into two parts (4x Trojans in each) in two different locations. So there is no single cable which carries all the current................
If it's a "bank", the groups of batteries are connected together somewhere, both positive and negative. If not, you don't have a "bank", you have two banks.

How do you charge the batteries? Unless you have two chargers and two alternators, you have a single bank.

Find where they connect together to supply the loads and that's where you connect your current measuring device.

BTW: Common wisdom would suggest that your arrangement is "less than optimal" because you won't get equal load sharing or charging with your arrangement and the different cable lengths.
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Old 17-11-2014, 08:25   #6
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Re: A Question for Electrical Geniuses

If you have a battery switch for both banks negatives must be connected. Just put the shunt in the middle of the negative cable. most shunts are designed to put on the negative cable
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Old 17-11-2014, 08:28   #7
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Re: A Question for Electrical Geniuses

Forgot to mark shunt
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Old 17-11-2014, 09:04   #8
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Re: A Question for Electrical Geniuses

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Forgot to mark shunt
He said no one cable carries all of the current. If there is one set of batteries in one location and another in a different location each with a wire on the negative post leading to loads, and another wire connecting the negative posts together then there is not the wire that you postulate to connect to.
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Old 17-11-2014, 09:42   #9
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Re: A Question for Electrical Geniuses

That's why I say that IF he has a battery switch that connects the two banks on the positive side he has to be wrong about the negatives not being connected together. If he truly has 2 separate banks that have their own charges and their own loads I don't have an answer. Edit. I would still think he could should put the shunt in between the negatives which he would have to add wiring for.
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Old 17-11-2014, 10:02   #10
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Re: A Question for Electrical Geniuses

If you have one bank splikt into two locations they have to be connected together somewhere. I have a negative buss bar that connects all of my load grounds and the negatives from from the two start batteries and the house bank. To put in a shunt I bought a short piece of 3/0 (3") and connected it to my buss and one end of the shunt. I took the Battery cables off of the negative buss and connected them to the other end of my shunt which was rated at 500 amps. I assume that you have two negative wires coming to a common point somewhere and this type of arrangement should be doable at that point.
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Old 17-11-2014, 10:09   #11
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Re: A Question for Electrical Geniuses

Quote:
Originally Posted by Dockhead View Post
I would like to measure DC current into and out of my batteries. But my battery bank is divided into two parts (4x Trojans in each) in two different locations. So there is no single cable which carries all the current.

So I need some kind of totalizer -- some instrument which can add the current from shunts or inductive sensors on two different cables and display the total.

Does such a thing exist?
I am not aware of one existing. However, it is not difficult to design such a thing. All you have to do is put a shunt in the negative return of each bank. Then put a separate A/H counter on each shunt (or a single two channel A/H counter). Then you know the A/H "account balance" of each bank. It's simple math to sum the two for total account balance.

This system will work even if you have the need to isolate one bank part of the time or you have different loads on the two banks (i.e. they are not truly parallel). The main issue is knowing when to reset the counters when each bank is "full". But that shouldn't be too hard to figure out.
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Old 17-11-2014, 10:19   #12
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Re: A Question for Electrical Geniuses

Bill's got this figured out.

It is very bad tech to split the house into 2 banks. Rewire it to be just one.
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Old 17-11-2014, 10:41   #13
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Re: A Question for Electrical Geniuses

Now have my own question for the Electrical geniuses, of which I am apparently not one . I am in the process of replacing my alternators. They have 3000 hours on them and the bearings were starting to sing a mournful tune. In any case the first one is rather straight forward as I simply moved the power and ground to the same posts on the new alternators. These are Yanmar alternators by the way with isolated grounds so it is my understanding that they have to be grounded through the ground(E) post and not through the chassis. Well, I get to the second one and I find the ground connection disconnected and full of sealant of some sort. Is there any reason the ground should not be connected on the second alternator?
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Old 17-11-2014, 10:50   #14
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Re: A Question for Electrical Geniuses

Why didn't you simply replace the bearings?
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Old 17-11-2014, 11:11   #15
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Re: A Question for Electrical Geniuses

wondering why people split the house batts into 2 groups? i have a power boat, but for yrs had that other kind called rag, or blow boats...went thru the split routine, start batt, swithches, etc [every switch causes a voltage drop!]...have helped those with 'combiners', while wondering why they bought the combiner hype? wired my house/start batts, using the 'KISS' principle [keep it simple stooopid'!] all house batts are 6v in series/paralell, in one bank, and 2 group 31`s in paralell for starting. xantrex makes a unit that will charge the start batt from the house batts, so i run the cable from the 130 amp alt to the B+ on the house, use the V3 regulator from amplepower.com in seattle...it does everything but the dishes! i went from 3 switches, to one, and it`s only used if i ever need to combine the start/house,, which has`nt happened in 20 yrs...guess what i`m asking is, why make things so complicated??...one thing i try to never let happen, is my house batts getting below
12.2/50%...clyde
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