charging voltage 13.2 enough?

sonus

Seaman Apprentice
Joined
May 6, 2005
Messages
35
Getting the boat ready for summer.I installed the battries yesterday,one optima blue top starting/deep cycle,one red top starting.I measure 14 volts at the alternator and 13.2 at the batts.I do have an isolator installed and I know a voltage drop is normal.But is 13.2 enough.After I'm out for the day I put my vector auto charger on them but I would like to see my dash voltmeter read a little higher while out ot the water.On a related issue the boats ammeter is always showing a discharge even when the motors running and there are no accesories being used.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: charging voltage 13.2 enough?

You don't say what engine, HP, or year so we can't be of much help. If you made the measurement at idle, the output is ok. The amp meter may be wired backwards but with everything off, even at 13.2 volts it should show a charge condition.
 

sonus

Seaman Apprentice
Joined
May 6, 2005
Messages
35
Re: charging voltage 13.2 enough?

Thanks Upinsmoke.Its an 84 volvo AQ200D,305 GM block.It's a trailer boat, readings taken at idle and at about 1500 RPM without much of a change.As for the amp meter,I don't think it's backward because if I turn on any lights or a blower it does dip further into the negative.I own this boat for a little more than a year and I've never seen that amp meter in the positive side,but I never got stranded even after ten hours on the water with a lot of stops and starts.I have done a lot of reading on this site over the winter and am much more knowledgable than I was a year ago and I am determined to put this boat into A-1 condition.So I'm trying to figure out if this charging system is working properly and what I can do to improve it.Thanks to all for any additional info or suggestions.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: charging voltage 13.2 enough?

Measure voltage at the alternator output or its input to the isolator. If its higher at that point you can assume the isolator is dropping a fair amount. Check where the amp meter is connected. For realistic readings, it should be between the isolator and the alternator. You might also check voltage with all accessories turned on. It may be the alternator is working but the output is low. It can be bench load tested and rebuild at any automotive electric shop (starter/alternator/generator rebuilder).
 

sonus

Seaman Apprentice
Joined
May 6, 2005
Messages
35
Re: charging voltage 13.2 enough?

Thanks Upinsmoke.The voltage at the isolator input is 14.0,so there is a .8 drop.I checked on the optima site for recommended voltages and it was around 13.3 for the blue and 13.65 for the red,or vice-versa,so I seem to be low at 13.2.I had the alt. rebuilt last year and it seems to be fine.I am considering doing away with the isolator and installing a battery combiner instead,probably buy it at west marine.Does anyone know of any drawbacks to the combiner?I'm thinking it should be an easy swap and solve the problem. Thanks to all!
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: charging voltage 13.2 enough?

Call me old fashioned but I prefer the simple ON-OFF-1-2-BOTH battery switch. Simple, versatile, durable and nothing (virtually) to go wrong. But they are not for those who tend to not understand how they should and should not be used.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: charging voltage 13.2 enough?

I not a fan of the optima batteries, they are too voltage picky, cost way too much, and never seen anyone who bought a second set.<br /><br />I also do not like batteries switches as I belive they kill more alternators than any other device. The problem is when turning the switch if at any point you have no battery connected with the motor running you blew your alternator diodes. Only takes a fraction of a second.<br /><br />I am a big fan of battery isolators, as they protect your alternator by having both batteries connected. Even if you turn your battery switch thru the off position with the motor running it will not blow your alternator.<br /><br />I have had a battery isolator since 1980 and have not had one battery that did not last at least 6 years. I do charge about once a month all season long and fully charge both batteries when I get home while I unload the fish and gear from the boat.<br /><br />In the old days the voltage drop problem you have could be solved very easy. Alternator that have an external regulator you just wire the battery back to the sense line of the regulator. Or the output of the isolator. This causes the regulator to adjust the voltage so the output of the isolator is the voltage the regulator is set for.<br /><br />Today most regulators are internal to the alternator and there is no way to feed battery voltage back to the regulator with out making internal changes to the alternator.<br /><br />In your case you could add a battery switch but keep your isolator to protect your alternator. The effect of this is your isolator would always charge both batteries as it does now. Yes you would still have a .7 volts voltage drop accrossed the isolator. However with the battery switch set to the 1 position then battery one would receive the full alternator output. In your case that would be 14 volts. Battery 2 would be the same as today. Change switch to position 2 and battery 2 gets full 14 volts. Even with a poor switch the isolator would still have a battery connect so the alternator diodes will not blow.
 

Andrew Leigh

Chief Petty Officer
Joined
Jun 17, 2003
Messages
431
Re: charging voltage 13.2 enough?

Hi,<br /><br />When a battery is flat and a charger / alternator is connected the battery will draw high current. It is usual to limit this current otherwise you would damage the charger / alternator. When the high current is drawn then there will normally be a corresponding voltage drop. Ohms law.<br /><br />As the back e.m.f. of the battery changes with charge so the voltage will increase as the current decreases.<br /><br />So if you are measuring 13.2V when totally flat I would not be concerned. However if the battery is in good condition then the voltage is too low.<br /><br />Charging voltages are critical for battery life, over or undercharging will permanently damage the battery. The following article will provide the voltage ranges per cell (remember to multiply by 6 for the 6 cells in your batteries).<br /><br /> Battery Charging <br /><br /><br />Cheers<br />Andrew
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: charging voltage 13.2 enough?

The only way a battery switch will damage a rectifier/regulator is if it is switched to OFF with the engine running or if the switch is not a make-before-break design and you change switch positions while the engine is running. That's why I said battery switches are ok but not for those that don't understand their purpose and how to use them.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: charging voltage 13.2 enough?

I agree with what Upinsmoke said 100 percent. Most good batteries switches are MAKE BEFORE BREAK but there are still many that are not. If you are not sure what type switch you have then always turn off the motor before switching.
 
Top