electrical voltage problem between banks

[billdorn]

I need some ideas on how to diagnose an electrical problem that just started. when running on bank 1 the alternator wont go above 12.5 volts or so according to dash. but when i switch to 2nd bank it runs at 14v. So i think i can eliminate the alternator as the problem.

I have 2 banks on a perko battery switch.

bank 1 has 2 batteries.
it is dedicated to the "house", which seems to be just the fridge as far as i can tell.
it also has a xantrex monitor hooked to it and it shows 12V and LOW, even with engine running.
if i measure the battery voltage right now sitting in the drive way of each battery it shows 13.7 volts??? but the boat gauge and the xantrex both show 12 volts? so 2 seperate gauges reading the same thing on bank 1.

bank 2 is is a single battery. it does have a bass tube directly wired too it.
measures 13.7 V with a meter right now in the driveway and also looked fine while running at around 14V.

I have a blue sea ACR that combines the banks and i can see the gauge drop from 14V to 12.5-13V whenever the 2 banks combine.

what should I test next?? Batteries are all mfg 2010, so not very old.

thanks

 

[Steve Craig]

Get all the batteries load tested. Any battery vendor should have the testing equipment.
Near new, yes, you'll still be surprised at the differences found in some cases.

 

[billdorn]

I bought one of these today and it says the batteries are low but good.

http://www.amazon.com/gp/product/B000K38UN6/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1

So traced out the system better. the on board battery charger is only hooked to bank 1, xantrex freedom 10. when plugged in it is charging 14V just fine now.

I got to thinking, the alternator is only running to one positive wire that goes to the switch. so the only thing different is the grounds. so i pulled all the grounds and cleaned and sanded the heck out of them on the battery terminal and it still only runs at 12v on bank 1 and 14 on bank 2.

just going to leave it plugged in and charging tonight. I need to figure out where the alternator senses the voltage from (wire the wires go) its all at the back of the engine in difficult areas to see in this boat.

 

[Steve Craig]

Putting the voltage tester on the + terminals of each battery(ies) you are seeing: 14V bank 1 with the built-in charger, 12V on bank 2 from the alternator.
Does the battery switch allow the batteries to connect to the same load ? ( Don't have a switch so unsure of application). Need to see a one-line on how the switch works.
Largest single load will be the starter. Full battery+ applied here, via relays, & requires a critical path directly back to the - battery terminal. Ground strap (-) "somewhere" on the block.
Another spot to check is directly at the alternator with the engine running.You should see about 14.4V between the single wire leaving it & any steel surface connected to it, engine block, mounting brackets etc.. Voltage drop between here & the battery can indicate a loose connection.

 

[ttmott]

The engine's alternator should be connected to the starter motor side of the main disconnect or the battery terminal of the starting motor. Consequently, the alternator needs to be on the engine's battery. The ACR simply is wired between the two battery banks and should not be switched with the main disconnect. The charger if multiple bank should be wired directly to the batteries or to the battery sides of the main disconnect. If the charger is a single bank it should be connected directly to the battery bank that has the highest AH which it appears to be the house bank. Now if the ACR is working correctly when the alternator is feeding the start battery at 13.0 volts or greater for 2 minutes the ACR will close and tie the two battery banks together so they both charge from the alternator. Conversely, when the charger is charging the house battery and is 13.0 volts or greater for two minutes the ACR will close allowing the batteries to be tied together and both charged from the charger. FYI, you should always keep the charger plugged in when the boat is idle; your batteries will thank you with many years do life.
So, if your grounds are all good the ACR may be defective; Or, if the ACR has the engine start disable option it may be wired incorrectly it would never close as designed.

 

[Mike Blake]

The last problem I had was bad connections. I cleaned all with sandpaper and not one problem after that. Fixed!! cleaply

 

[billdorn]

turns out I had a bad orange wire on the starter and when i pulled on it it broke off the spade. what threw me off is the volt meter at the dash reading 14V on bank 2, but only 12V on bank 1. seems like i should have had a problem no matter what bank was sending power to the starter.

my switch will merge the 2, and then would drop to 12v again. the ACR i have hooked up will auto join the 2 banks regardless of which bank is switched on. i have it this way because my xantrax charger only charges bank 1 regardless of switch position. (how it came, and i just figured this out)

but after i fixed it, a new problem arose. it cranked for a split second and then lost power on bank 1. then i couldnt find voltage from the battery to the switch. so i ripped out the cable thinking there was a problem, didnt see one, but it back in. and then it worked again. 5 minutes later same thing, it wouldnt crank, and i tossed a volt meter on the battery and it was measuring 6 volts. Does that mean i also have a battery cell problem?? then 2 minutes later it was fine again. its starting to worry me. I'm going to buy a new cable from battery to switch. only because its easy to replace.