OptiMax Rough Idle When Cold - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  OptiMax Rough Idle When Cold

search | FAQ | profile | register | author help

Author Topic:   OptiMax Rough Idle When Cold

aussiejake posted 07-23-2008 07:27 PM ET (US)
I fixed the rough idle when cold on my Mercury OptiMax 135-HP motor by keeping my batteries at 100-percent charge ( or 12.8-volts). For once it was a cheap fix. ;-)
I run two batteries on the boat, both 800-cold cranking ampere rated. Is it of any benefit to start the motor using both batteries together?
Does it give it double the cold cranking amperes? Does it help the batteries to last longer?
I have always just started on one battery and when leaving the dock I turn the isolator to "2" so I can charge them both up while heading out to sea.
cheers
Jake

seabob4 posted 07-23-2008 08:38 PM ET (US)
Jake,
I'm sure our friend JimH will suggest moving this to "Small Boat Electrical", but, to best see what state your batteries are in, follow this. 12.8 Volts should be your battery "rest" voltage, when their is no load on them, nor any charging device sensed. Start your motor with the battery switch on "both", then check each batteries voltage with a multimeter with the engine at idle. You should see a small increase on both batteries. This will tell you your charging circuit is working.
There is no harm in starting the motor with the battery switch on "both". But that method won't increase your total starting amperage. Can you imagine throwing 1600 amps of juice at your starter? No, didn't think so. It just lets a stronger battery help out a weak one. Just never turn your battery switch to a position that will move through the "Off" position when the motor is running, unless you know for certain that your battery switch has a feature called an "Alternator Field Disconnect". This will fry the alternator's diode in a heartbeat.
jimh posted 07-23-2008 08:39 PM ET (US)
Connecting batteries in parallel combines their current output. If two batteries are each rated for 800-CCA, when they are in parallel you have the equivalent of 1,600-CCA rating.
jimh posted 07-23-2008 08:45 PM ET (US)
The Mercury OptiMax is reported to be sensitive to the battery voltage and particularly when running at low speeds, where the motor is probably a net consumer of power from the battery as its alternator has not produced any excess current. At low speeds the battery is probably still experiencing some discharge or at best a very small charge, so its terminal voltage is probably going to affect the operation of the OptiMax.
I am glad to hear you improved the motor's running characteristics at low speed by keeping the battery well charged and near optimum terminal voltage. That is a good tip for other OptiMax owners.
seabob4 posted 07-23-2008 09:11 PM ET (US)
JimH,
Connecting in parallel does not double output amperage, it doubles amp-hour capacity. Check to see if 4 gauge cable can handle 1600 amps without melting.
Treypescatorie posted 07-23-2008 10:02 PM ET (US)
By using a battery with a higher current rating , it doesnt mean that the starter sees that current. It just means that that much current is available if needed. Its like your house service. If it a 200 amp service , it means that all the circuits in the house can draw 200 amps max. If your tv is the only thing on in the house it will not draw 200 amps. Capisce?
seabob4 posted 07-23-2008 10:13 PM ET (US)
Capisce.
aussiejake posted 07-23-2008 10:56 PM ET (US)
Thanks for all this great info guys.
I suppose the best solution is just keep the batteries at full charge.
Jake
aussiejake posted 07-24-2008 01:20 AM ET (US)
Parallel Connection -- Batteries connected in parallel means that all the Positive (+) terminals are connected together, and all the Negative (-) terminals are connected together. Batteries wired in parallel supply the same voltage but higher current. The amp-hour ratings add for each battery, but the voltage stays the same. New batteries should not be paralleled with old ones. (See also Series Connection).

Series Connection -- Batteries connected in series have the Positive (+) terminal of one battery tied to the Negative (-) terminal of the next battery. Power is taken from the two terminals at the end of the series string. Batteries wired thus supply the same current but higher voltage - for example, four six-volt batteries in series will give 24 volts. The amp-hour rating will be that of the smallest battery if different types are connected.
this was interesting and may help in the discussion.
cheers
Jake
jimh posted 07-24-2008 08:57 AM ET (US)
Please use SMALL BOAT ELECTRICAL to discuss vessel wiring and battery distribution. This discussion is on the topic of the Mercury OptiMax rough idle characteristics when cold and the affect of battery voltage on that condition.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: OptiMax Rough Idle When Cold
aussiejake	posted 07-23-2008 07:27 PM ET (US) I fixed the rough idle when cold on my Mercury OptiMax 135-HP motor by keeping my batteries at 100-percent charge ( or 12.8-volts). For once it was a cheap fix. ;-) I run two batteries on the boat, both 800-cold cranking ampere rated. Is it of any benefit to start the motor using both batteries together? Does it give it double the cold cranking amperes? Does it help the batteries to last longer? I have always just started on one battery and when leaving the dock I turn the isolator to "2" so I can charge them both up while heading out to sea. cheers Jake
seabob4	posted 07-23-2008 08:38 PM ET (US) Jake, I'm sure our friend JimH will suggest moving this to "Small Boat Electrical", but, to best see what state your batteries are in, follow this. 12.8 Volts should be your battery "rest" voltage, when their is no load on them, nor any charging device sensed. Start your motor with the battery switch on "both", then check each batteries voltage with a multimeter with the engine at idle. You should see a small increase on both batteries. This will tell you your charging circuit is working. There is no harm in starting the motor with the battery switch on "both". But that method won't increase your total starting amperage. Can you imagine throwing 1600 amps of juice at your starter? No, didn't think so. It just lets a stronger battery help out a weak one. Just never turn your battery switch to a position that will move through the "Off" position when the motor is running, unless you know for certain that your battery switch has a feature called an "Alternator Field Disconnect". This will fry the alternator's diode in a heartbeat.
jimh	posted 07-23-2008 08:39 PM ET (US) Connecting batteries in parallel combines their current output. If two batteries are each rated for 800-CCA, when they are in parallel you have the equivalent of 1,600-CCA rating.
jimh	posted 07-23-2008 08:45 PM ET (US) The Mercury OptiMax is reported to be sensitive to the battery voltage and particularly when running at low speeds, where the motor is probably a net consumer of power from the battery as its alternator has not produced any excess current. At low speeds the battery is probably still experiencing some discharge or at best a very small charge, so its terminal voltage is probably going to affect the operation of the OptiMax. I am glad to hear you improved the motor's running characteristics at low speed by keeping the battery well charged and near optimum terminal voltage. That is a good tip for other OptiMax owners.
seabob4	posted 07-23-2008 09:11 PM ET (US) JimH, Connecting in parallel does not double output amperage, it doubles amp-hour capacity. Check to see if 4 gauge cable can handle 1600 amps without melting.
Treypescatorie	posted 07-23-2008 10:02 PM ET (US) By using a battery with a higher current rating , it doesnt mean that the starter sees that current. It just means that that much current is available if needed. Its like your house service. If it a 200 amp service , it means that all the circuits in the house can draw 200 amps max. If your tv is the only thing on in the house it will not draw 200 amps. Capisce?
seabob4	posted 07-23-2008 10:13 PM ET (US) Capisce.
aussiejake	posted 07-23-2008 10:56 PM ET (US) Thanks for all this great info guys. I suppose the best solution is just keep the batteries at full charge. Jake
aussiejake	posted 07-24-2008 01:20 AM ET (US) Parallel Connection -- Batteries connected in parallel means that all the Positive (+) terminals are connected together, and all the Negative (-) terminals are connected together. Batteries wired in parallel supply the same voltage but higher current. The amp-hour ratings add for each battery, but the voltage stays the same. New batteries should not be paralleled with old ones. (See also Series Connection). Series Connection -- Batteries connected in series have the Positive (+) terminal of one battery tied to the Negative (-) terminal of the next battery. Power is taken from the two terminals at the end of the series string. Batteries wired thus supply the same current but higher voltage - for example, four six-volt batteries in series will give 24 volts. The amp-hour rating will be that of the smallest battery if different types are connected. this was interesting and may help in the discussion. cheers Jake
jimh	posted 07-24-2008 08:57 AM ET (US) Please use SMALL BOAT ELECTRICAL to discuss vessel wiring and battery distribution. This discussion is on the topic of the Mercury OptiMax rough idle characteristics when cold and the affect of battery voltage on that condition.