What sealant to use?

potter water · Posted: Tue Apr 10, 2012 11:32 am Post subject:

JUst a word to be cautious about the OEM gauges we use for our outboards. They are notoriously off in my experience over the last 15 years. I always carry a digital voltmeter that I can trust, and check gauges on each new boat or motor install. That allows me to mentally tweak what I'm seeing on the gauges and have a more realistic view of what is being indicated on the gauge. If gauges are right on the money great. I've not done the digital voltage meter checks on my new to me twin Suzies, but as I'm replacing the 6 year old batteries this year, I'll be making my own calibration table up for the analog "in dash" meters.

Ashley Lynn · Posted: Tue Apr 10, 2012 2:36 pm Post subject:

Thanks again for all the guidance.

NORO LIM · Posted: Tue Apr 10, 2012 3:52 pm Post subject:

thataway · Posted: Tue Apr 10, 2012 6:14 pm Post subject:

One of the problems is that outboard motors are poorly regulated. (Some better than others), but with Suzuki, Yahama and Honda I have often seen voltages of 14.7 volts. My Suzuki 140 runs 14.4 to 14.7. I don't have enough time on the Honda 90 (16 amp alt on the carbonated model) and using the Link lite to know what the voltage characteristics will be, but the 130 I had on the C Dory 25 (measured by Link 10) was in the 14. 4 to 14.7 range. No harm to my AGM batteries on any of these motors.

Generally you want to avoid gassing of any batteries--and it is a variation of current and voltage to get the best charge characteristics. AGM will take up to 30% of their capacity per hour with no problems. On my RV and some other units with large battery banks, I have a temperature sensor on the battery charger (130 amps 4 stage on the RV). The temperature sensor is important to prevent gassing.

Here is a quote from one battery expert:
"The charging of AGM batteries can be done by applying a constant-voltage, where the charging voltage is held to a range of 2.3 to 2.6V (at 25°C) and the current is allowed to vary. This lends itself to higher rates of recharge without damage or reduction of lifetime. Complete charge times of less than 1 hour are possible (C/1 rate). " AT 2.4 volts per cell, this is 14.4 volts (which is generally accepted as the ideal charging voltage in absorption phase for AGM)--but at 2.6 this is 15.6 volts! Optima states that their batteries can be charged at up to 15 volts, both with alternator, charger and cyclic use. Keeping the charging voltage at 14.4 volts is very acceptable--if your outboard motor is that well regulated. However, for the relitatively short periods we run our motors going up to 14.7 volts most likely will not shorten the life of the battery.

NORO LIM · Posted: Tue Apr 10, 2012 9:04 pm Post subject:

Thanks, Bob, for all the good information.

My tentative conclusions about the premature demise of my AGMS:

1. The smaller Yamaha engines' alternators may not be as well regulated as the larger ones. I have two F50's. I do frequently see 14.8 volts on my gauges.

2. I probably run the engines for longer periods than average. Last year's 2000 mile trek, for example, included many long days of running with nothing other than the engine alternators charging the batteries. A previous similar trip with flooded cell batteries caused no problems. It may be that a little bit of 14.8 in shorter bursts won't hurt.

Whatever the case, I'm back to using flooded cell batteries.

(Note to Admin - we seem to have strayed from the thread title a bit. Maybe some of this on batteries could be moved?)