Battery Voltage Motor Starting Question

[eric1966]

Hi I was wondering if anybody would know what the minimum battery voltage required to start a Mercury 250 Pro xs is ? I have new Odyssey 2150 batteries and if running the electronics how low could the voltage go before it would affect the Starting Motor ?
Thank you

[Shef]

You shouldn't have to worry about being able to start it with that monster. Don't believe the volt reading from you electronics either. If you really want to know, put a meter on the pos and neg posts. I run the same battery and power the following on my 2010 Puma: 2 power poles, livewells set on 3 (both recirc and pump in in the summer), HDS8 & 7, structure scan, LMS 332, hyd jackplate, Merc 250XS and the stero when anyone wants it on.

[eric1966]

Hi I was just wondering how many hours I could run an HDS 10, 8 and Structure scan before there would be an issue starting ?

[lpugh]

23.3 hours to pull that battery down to 10.5 volts, so I think about 12 hours of constant use without running the big motor would have you at about 12.40 volts which would still start it ok. That is with the back lights on on both units, you would get at least 25% more time with the back lights turned off.

Reserve Capacity, (RC) is a battery industry rating, defining a battery's ability to power a vehicle with an inoperative alternator or fan belt. The rating is the number of minutes a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery. The higher the reserve rating, the longer your vehicle can operate should your alternator or fan belt fail.

As Shef mentioned do not count on your electronics to read the voltage, there are to many voltage drop issues to be accurate. Check it at the source. If the electronics are reporting more than .300 volts lower reading you need to address that and find the cause!

Batteries are kind of like fuel tanks and you are the only one that can determine how much gas or Battery capacity that you actually need.

I personally run three Optima 31 (50 amps less reserve than the battery that you have), One of those three is also my cranking Battery for a 3.0 merc efi and I use a 101 lb trolling motor.

I have fished many tournaments in tidal conditions with wind running a 2 HDS units and my live well pumps most of the day and have never dropped the cranking battery to less than 80% charge.

The question that you have needs to be evaluated by you. There are low cost battery testers out there (less than $100) that will help determine what you need.
I test my batteries after every trip for state of charge and health (reserve capacity). By monitoring your batteries this way you will get a feel for what you actually need and plenty of warning when one is starting to fail.

My three battery system works great for me, does not mean it will for you. Running more battery than you need is a lot better than not having enough, the same as running out of gas! It just means a little xtra cost and weight. I also only put as much fuel in the tank as I am sure that I will need for the day. 20 gallons less fuel and a 60 lb lighter battery package helps keep my Bass Cat flying!

That motor requires a lot of battery and if it were mine I would not run it off a trolling motor battery, butt I would use the lighter grp 31 Optima. Nothing smaller. I will say that the battery you chose is a great battery and if it can not git r done, none will.

Be sure to recharge it after every trip, do not count on the big engine to do it for you.

[EuropeanAM]

Good information above. Now let's talk about what your 250 REQUIRES to start.

Simply put: When battery voltage drops below 11.0VDC, "Strange things are bound to happen". And by strange... it can be a wide array of problems, ranging from a no-start condition, to rough idle, warning horns, engine guardian (preventing acceleration), etc. etc.

So the short answer.... if voltage is dropping below 11.5 VDC, it's probably time to go for a run and put some juice back.

One of the huge benefits of these AGM batteries is that they RETAIN most of their cranking capacity, DESPITE drop in voltage. The advantage is that you will likely be able to get the engine to fire off after running your accessories for extended periods (despite lower initial voltage), as the battery's OVERALL capacity means that the voltage DROP during the starting cycle is not as great (as compared to lead-acid batteries).

[eric1966]

Thank you for the advice this is what I was looking for

[lpugh]

Don I assume you are talking about 11.5 during cranking or static! Did not think that motor would start below about 12.0 12.2 static volts. I have not personally checked that motor butt I would think it would have a least 1.0 volt drop while cranking even with that big battery? No first hand experience with that one just curious, and in need of more education.

Thanks Don


Modified by lpugh at 7:47 AM 5/15/2011

[JAZII]

It will start just below 11.6 volts, BUT IT WILL GIVE AN ALARM AND BE IN GUARDIAN MODE UNTIL VOLTAGE GOES ABOVE 11.6 VOLTS.

JAZII

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by JAZII &raquo;</td></tr><tr><td class="quote">It will start just below 11.6 volts, BUT IT WILL GIVE AN ALARM AND BE IN GUARDIAN MODE UNTIL VOLTAGE GOES ABOVE 11.6 VOLTS.

JAZII</td></tr></table>

In general, this is correct (provided that adequate AMPERAGE CAPACITY is available to actually activate the starter, while still powering the large array of electrical devices on the engine).

And yes Leon, I was speaking of STATIC voltage, based upon one of the Recommended AGM batteries (not a lead-acid battery, which at such voltage would only have approximately 50-60% of it's advertised Amperage capacity available).

The "perfect world" answer is that your 12V battery should always remain at 12V or above voltage.

That being said- we ALL know that folks reading this forum FISH. And hopefully- they occassionally find that perfect spot that they're not leaving until they are sure they've caught the best bag. This can sometimes mean SEVERAL hours of running livewells, two or more graphs, and various other "assistance" devices.

It's THIS day.... when you realize you've allowed battery voltage to drop down to 11.7, 11.6, or maybe even 11.5 or lower: that will SEPARATE A BARELY ADEQUATE battery from a REAL BATTERY.

Most of the AGM's on the list will START the engine under even these conditions- and once battery voltage again climbs to 12 volts or above prior to accelerating, the PCM will allow for normal operation (though it likely will have logged a low battery voltage fault in the Freeze Frame "Fault" History).