Voltmeter and battery isolator

[timjet]

Hi Folks,
I just bought a 98 Carver 35' ACMY and am in the mist of doing some much needed upgrades. I've added a freshwater flush, additional fuel filters for both the engines and genset and an oil change system. The pocket book is taking a hit, but I'm almost there. I haven't even taken the boat out yet!!

I want to add a digital voltmeter because the OEM on the helm is difficult to get an accurate reading. I have 3 battery banks, 2 AGM batteries on battery selector position #1, two AGM's on battery selector position 2, and a single AGM solely to start the genset.
All the batteries are new and recharged by a Charles 5000 series batt charger. I think I need to have the charger modified for the AGM batteries, but not sure as I haven't been able to find the serial number on the charger.*

Hears my question: If I install a voltmeter, I think I will need to install isolators on the battery banks with two batteries, otherwise the voltmeter would just read bank voltage, not individual battery voltage. Correct?? If so how is it best to do this? Is the isolator installed electrically between the two batteries on a bank. If so how would you parallel them when necessary?


I guess the easy solution is just to add a battery switch between each battery on a *bank and turn it to the off position to check voltage. That would seem like a lot of work and expense just to check individual battery voltage. Is there an easier way?


-- Edited by timjet on Friday 28th of May 2010 04:56:38 PM

 

[C lectric]

Try using a rotary multi position switch to select which battery you want to read. They are available in many variations, available from places like Newark Electronics, Electrosonic, and others. You don't need a heavy duty one since your voltmeter should draw only a few milliamps.

That way there is no connection between banks. Just ensure it is a break before make type - usually are.


Radio Shack or Circuit City* may still have them even though they are now into more finished products rather than components

-- Edited by C lectric on Friday 28th of May 2010 11:12:17 PM

 

[timjet]

I don't think that will work. My battery bank consists of two batteries connected in parallel which means there is a cable connecting the two positive battery terminals together and a separate cable connecting the two negative terminals together. An additional cable then routes from the positive terminal of the paralleled batteries (doesn't matter which battery positive terminal) to the battery selector switch. The negative side is routed the same way except the separate cable goes to ground. Under this arrangement if a voltmeter is attached to either battery the voltage read is the voltage produced by the battery having the greater voltage. Even if you have a wire connected to each batteries positive terminal and through a rotary switch to a voltmeter, the voltmeter will read exactly the same regardless of which battery you have selected with the rotary switch. The battery with the lower voltage is in essence* being charged by the battery with the higher voltage.

 

[hollywood8118]

If it is always used in the current configuration why worry about it??. It is one battery... it doesnt matter if " one battery charges through the other ". Now, if you want to be able to use one, or both at a time a switch change is in order,
good luck

 

[C lectric]

Now I understand. You want to read the voltage of each individual battery, not the battery bank. I thought you wanted to read each battery bank, for that the rotary switch will work. Just fuse each lead close to the battery. Guess I jumped to a delusion.

To do what you want to do will complicate your wiring
.
To separately read each individual battery you will need diodes isolators, as you surmised, which will cause their own set of headaches, I think far more than you will gain.

I guess the other way would be a whole mess, well one per bank, of H.D. paralleling relays, continuous duty, to be deactivated thus separating the bank into individual batteries which can then be read.

Most people read the banks - so yes it is an average of however many batteries are in that bank. However, unless there is something wrong with the wiring, that is perfectly good as the batteries should contribute to the load and recharge equally. This does need some attention about how the batteries are connected to the load.

Go to this site for the best connections:
http://www.smartgauge.co.uk/batt_con.html

The only time you really need to read each individual battery voltage is if you suspect there is a problem with a dieing/dead cell in one. Then, for testing, separate them. Or get someone down with a battery conductance meter which can read individual batteries condition even when still connected as a bank. These meters, unless you just want one or if you want to start hiring out, are still a mite expensive yet to just have around. I'm still watching. .

A question: bank # 1 and bank #2, are they both house banks, or is one a house and one for the engine with # 3 for the generator.

 

[timjet]

C lectric wrote:
A question: bank # 1 and bank #2, are they both house banks, or is one a house and one for the engine with # 3 for the generator.

I spent several hours last weekend trying to figure out the DC electrical system. I disconnected all the batteries and thinking as I reconnected each one I would determine how each battery was banked and which bank it was connected to.*Damnedest thing happened, when I disconnected all the batteries, I was still getting power to the house items thru the #1 battery selector switch position. I just couldn't figure this out. With all batteries disconnected how could anything be powered. Was I getting free power??*With my frustration level about to be exceeded only by my lack of patience, I noticed a battery tucked in the rear of the ER center walkway in a position that was impossible to see unless you were looking specifically for it.*Mystery solved and*unfortunately*no free power.*

Bank #1 is connected to battery selector position one and is also connected to the port engine. Bank #2 is connected to battery selector position two and is connected to the stbd engine. Bank #3 which consists of only one battery is only available to start the genset. It is not possible to use the opposite side battery bank to start an engine, or the genset, however either bank can be used to power the house circuits.


As a former sailboater I felt it important to know the condition of each battery, especially when the only way to recharge a battery was to start the engine.*
This of course is a very different boat and with a genset and 5 batteries, it is not as important to know the condition of each battery. I will leave well enough alone.


Tim

*

 

[FF]

IF you plan on monitoring the alt on the running engine , my preference is to pickup the voltage at the top of the starter solenoid.

This will give the same reading with the engine operating as anywhere else ,

BUT it allows the start system and starter to be monitored while actually starting.

I also much prefer RV solenoids as the combining method to join the engine and house while operating.

No voltage drop for the house set to fool the engine volt regulator.

Cheap $18. each and easy to trouble shoot.

 

[Fotoman]

Not sure why you would want to read individual battery voltage of a bank. The idea of putting them in parallel is that the operate as one. Unless I am not understanding the situation correctly.

 

[timjet]

Isolating each battery in a bank allows you to read the voltage of each individual battery. A battery that has a bad cell will show low voltage. The good battery in a bank will constantly be trying to charge the battery with the bad cell since it has the higher voltage. The net result is that the good battery is being constantly discharged. Having the ability to read the voltage of each battery will give you a heads up on a failing battery.

 

[FF]

"The net result is that the good battery is being constantly discharged. Having the ability to read the voltage of each battery will give you a heads up on a failing battery."
"

True BUT a V meter is a poor way to find the bad cell.

A hydrometer , with a temp compensating chart is the BEST way, costs very little and can be done each time you water the bank, if you are that compulsive.

Most folks simply purchase batts as a set , and usually wired together they age as a set.

 

[timjet]

Delfin,

Thanks for the congradulations. I've haven't enjoyed the boat yet, just worked on it. I'm getting burned out, so will take a break and get out an enjoy it. Here in So Florida the boating season, (if you can call it that) is over. It's very hot and not real comfortable. No matter, I'm going to enjoy it came hurricane or high water.

Your suggestions make sense. However it is very difficult to disconnect the batteries from each other due to their location. I've found that the easier a maintenance action is the more likely it is to get done. Regardless I understand your thinking and have given up on the idea of an isolation system. I however am going to take out my battery charger and reset it for charging AGM batteries. It too is not easy to get to, but will remove it and send it to Charles the manufacturer and have them recalibrate it for AGM's. Tell me more about adjusting the alternator output.

Do you have recommendations for a fuel sending unit. I need to replace mine.

 

[timjet]

FF,
I don't think the AGM's have the ability to check the fluid. Probably the best way is to recharge, let set for an hour or two and then put a load on the battery and check for voltage drop. I would only do this if I suspect a problem.

 

[FF]

The best way to monitor a batt set is to use an E -meter ,or similar product , and let IT monitor the charge discharge profile.

The fancy units from Bogartengineering.com can plug into a computer and give more history and information than anyone could possibly use.

$200 minibucks and your batt living is easy , cruising is really easy , and by never being KILLED (low voltage , over voltage alarms) the even cheap Sams Club or Sears golf cart batts will do half a decade.

Trojans 7 - 8 years and Surettes a full decade +.

 

[Avista]

Hi Tim,

Glad you are enjoying the boat.* I sent you an email, but thought I would post this here for the benefit of anyone interested.* I have a similar setup.* I have a BIG battery (1530 MCA Rolls Surrette) that is the port engine start battery and house battery.* I have an 8D battery that is the starboard engine start battery and can back up the house, and a third smaller group 31*battery that is a dedicated starter battery for the genset.
I don't monitor the genset battery, but check the specific gravity once a month.* the other batteries are monitored by a Link 2000 from Xantrex.* By using a shunt, I can monitor either battery and see it's state of charge, amps used, remaining amp hours, and more.* I no longer am using a big*inverter, but do like to know how much juice I am using on the hook as the dc fridge is running and I use a small inverter for the microwave and stereo.* With the link, I can make sure that I get the most life out of the house battery by recharging before it goes below 50%.

 

[timjet]

Hi Marc,
Will e-mail you soon.
I considered installing a battery monitor like you describe, but will get some time on the boat before I make a decision.
I have decided to install a digital voltmeter. They can tell you a lot about the state of charage of the battery. A boat maintainence book I have lists the state of charge of a battery based on it's voltage, but a digital meter is necessary to determine that. Since AGM batteries were developed after the book was written I'm not positive the figures he gives apply to AGM's. I need to do a little research on that.
I'll be down at the boat this weekend and plan on removing the battery charger. I called the manufacturer and found there is a setting that needs adjusting for AGM's. The PO replaced all 5 batteries in February at a cost of over $1500 and I know he didn't have the charger adjusted for the new batteries. The darn thing like everything else on this boat is difficult to get to.