Moderated Discussion Areas
  ContinuousWave: Small Boat Electrical
  Estimating Electrical Demand

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Estimating Electrical Demand
HMBJack posted 02-28-2005 11:57 AM ET (US)   Profile for HMBJack   Send Email to HMBJack  
I have two Honda four-stroke motors on my transom: a 90-HP and a 5-HP. I carry only one battery: a deep cycle with 500 cold cranking amps. It has a reserve of 100, but I do not understand what that means.

When trolling for salmon, I will shut down the main motor and use the auxiliary. The auxiliary motor has no alternator.

If I am trolling for 2 or 3 hours and I have all of my electronics on, should I be concerned that my battery won't have enough energy to start the main engine?

My electronics (operating from the battery) are as follows:
- a AM/FM/CD radio + two 6" speakers(50 watt per channel)
- a Garmin GPS (hand held powered with 12v connector)
- a Humminbird Fish Finder
- a 20 watt per channel VHF radio

Should I be worried?

If yes, possible solutions include:
1. carry an extra battery, or
2. install a 3 amp charging kit on the 5-HP which should offset any energy I use while trolling


Chuck Tribolet posted 02-28-2005 01:16 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Without the AM/FM/CD it shouldn't be a problem. You're pulling
less than one amp assuming the VHF is quiet and you aren't
transmitting. (BTW, it's probably a 25W VHF, that's the max
and I've NEVER seen a 20W).

The entertainment system is another story. 50 watts is about
four amps PER Channel. Some units pull full power even when
turned down, some don't.

Cranking amps don't matter in this application. Amp-hours
do. Your battery is probably around 60 amp-hours, so it
will run the GPS/fishfinder/VHF for about 60 hours, and
the stero for about 7.5 hours.

I think I'd put the alternator kit on.


Whaler Lover2 posted 02-28-2005 02:28 PM ET (US)     Profile for Whaler Lover2  Send Email to Whaler Lover2     
Go for the charger kit or get a bigger battery, 500CCA is pretty small.

I also vote skip the tunes and you should be ok. At least with the kicker you wont get stranded

JustinAndersen posted 02-28-2005 02:40 PM ET (US)     Profile for JustinAndersen  Send Email to JustinAndersen     
I'd go with the alternator kit as well. That way, if your battery is dead, you can pull-start the 5-HP and charge the battery. I do it all the time with my kicker.
HMBJack posted 02-28-2005 03:07 PM ET (US)     Profile for HMBJack  Send Email to HMBJack     
Thank-you for your input.

Conceptually, I like the idea of GENERATING electricity while the 5-HP is running (and while I'm drawing energy from the electronics).

Perry posted 02-28-2005 03:44 PM ET (US)     Profile for Perry  Send Email to Perry     
I've pull started a Honda 90 before, it started on the second pull. The motor came with a pull cord so one day I decided to test it and see if it would start. Sure enough it did!
bsmotril posted 02-28-2005 04:49 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
If you put an inexpensive ammeter across the battery, you'll know for sure. Anything else is speculation unless you have all the specs for the electronics current draw, and alternator output at the RPMs you run, then you can calculate it mathmatically. You can get an ammeter for less than $50. Cheap insurance.
Hudsojo posted 02-28-2005 05:35 PM ET (US)     Profile for Hudsojo  Send Email to Hudsojo     
What's the approx. cost of the alternator kit - with installation? I think I may add one as well.
HMBJack posted 02-28-2005 06:39 PM ET (US)     Profile for HMBJack  Send Email to HMBJack     
The alternator kit for the Honda 4 stroke 5-HP is $152 (PN 06310-ZV1-A00).

Interesting observation: the responses on this forum all pretty much suggest installing the alternator. Another popular forum, devoted to Bay Area Fishing all suggest carrying a second battery (not one suggested installing an alternator). Not sure but I'm now leaning towards carrying a second battery. I fish in the ocean off San Francisco and it is a very unforgiving place if you break down. One interesting remark was "you could actually pull start the Honda 90". One guy tried it and the bloody thing roared to life on the second pull (a starter chord is included in the tool kit). Interesting...

high sierra posted 02-28-2005 07:04 PM ET (US)     Profile for high sierra  Send Email to high sierra     
HMBJack, An modern outboard will start with a rope if the battery is charged. When the voltage drops low enough, it will NOT fire the ignition to work even though the motor turns over. An orbital battery by Optima is a great choice as second battery with a switch to only use one battery at a time. Wal Mart was carrying a deep cycle/starting batery that was excellent at 1000 amps.. I would have a battery of 900 to 1000 cranking amps ,(CA.) They are usually about 700 to 800 (CCA). A batteries power at 32 degrees. Cold cranking amps.) The way you are set up is not sufficient when problems arise. High Sierra
HMBJack posted 02-28-2005 07:07 PM ET (US)     Profile for HMBJack  Send Email to HMBJack     
Thank-you. It is the advise and knowledge of members like you that might save a life someday (no kidding).

I will install a second battery + switch with the spec. you suggest.

ocuyler posted 02-28-2005 07:22 PM ET (US)     Profile for ocuyler  Send Email to ocuyler     
I believe that for offshore situations, a second battery is mandatory. I suggest (2) 100 amp/hr combo starting/deep cycle lead/acid or better. The should be isolated from each other with an 1/2/Both/Off switch. #1 is ONLY a starting battery. #2 is a house battery for when you have no charging going on.

I would also install the charging system on the kicker.

And listen to all the music you want...

steelhead5 posted 02-28-2005 07:25 PM ET (US)     Profile for steelhead5  Send Email to steelhead5     
Ive got a montauk with a similiar setup. I think with the weather we have up here you should put duel batteries up in the cc. I did, and my boat is trimmed out so nice, and I have a heavy suzuki df70 and a honda 8-HP on the transom. Its nice to have that peace of minda of lots of amps if needed to start.
Lil Whaler Lover posted 03-01-2005 09:33 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     
A simple solution could be to take a battery pack when you go out. It would permit a jump start if necessary and is very inexpensive. Mine also has a built in light and small air compressor. Very handy to have around.
Chuck Tribolet posted 03-01-2005 09:48 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
high sierra, a modern outboard will only start with a rope
IF it's equipped with a rope. My Evinrude 90 isn't, and it's
not an option.


Perry posted 03-01-2005 12:52 PM ET (US)     Profile for Perry  Send Email to Perry     
A modern outboard like my old Honda 90 will start with a rope with a battery that has some juice (will turn over but not fast enough), but not a totally dead battery. I think that if the battery had enough amps to start you at the ramp and looses some amps while fishing or anchored, it should have enough power to pull start.
17 bodega posted 03-01-2005 01:00 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
I like the idea of the battery pack. I just discovered what I thought was a dead battery at the boat ramp the other day. It was poor and corroded terminals.

I am now carrying a spare, fully charged deep cycle marine battery on board for emergencies.

high sierra posted 03-01-2005 03:22 PM ET (US)     Profile for high sierra  Send Email to high sierra     
Chuck , some of the older? motors haven't the ability to be rope started. Most new motors come with a rope, believe it or not. The main thing is the computer in a majority of the motors today require a near full battery to make them fire, even though the motor will crank over at a lower voltage. I'm sure there are exception as will be pointed out by someone. For example the E TEC electrics are self excited and will start with a dead battery, so says the dealer. Hate to find out the hard way. high sierra
CHRISWEIGHT posted 03-01-2005 04:34 PM ET (US)     Profile for CHRISWEIGHT  Send Email to CHRISWEIGHT     
Has anyody successfully started a 90-HP Mercury with a rope? We gave it a go a few days ago and could not rope start it.
jimh posted 03-02-2005 09:10 AM ET (US)     Profile for jimh  Send Email to jimh     
I think you are in the minority here by having more outboard motors than batteries aboard. The usual ratio is 2:1 or higher in favor of batteries.

One solution to this problem would be to have two batteries. The second battery is wired only to the electronics. It receives charging current from the main engine via a voltage sensitive relay. The relay only operates when the voltage of the main starting battery is above 13.2 volts. This will occur when the main engine is running and supplying battery charging current and has fully charged the main battery.

The second battery for only electronics can be smaller. A small Group-24 or a deep cycle of similar size.

With the set-up I propose you will have these advantages:

--the electronics can never discharge the main starting battery;
--the electronics will run completely separate from the main battery and will not be affected by voltage spikes or sags that occur during engine start;
--the starting battery will always receive charging current when the main motor is running;
--the electronics-only battery will receive charging current only after the main battery has reached full-charge level.

A voltage sensitive relay (VSR) only costs about $75. A second battery will be about the same or less. For $150 you will have much piece of mind.

Cicada posted 03-02-2005 10:21 AM ET (US)     Profile for Cicada  Send Email to Cicada     
I think we have parallel threads going here that relate to each other. I've been evaluating the electrical system for the Outrage and have many of the same concerns and questions.

A little research into the VSR from BEP Marine shows that the maximum size of the house battery you can use is related to the charge output of your motor.

Unfortunately with the anemic output of the Johnson 150 the VSR wouldn't work properly with a battery above 60 AH.

What's the charge output on the Honda 90?


Cicada posted 03-02-2005 10:27 AM ET (US)     Profile for Cicada  Send Email to Cicada     

You may find some of the information and comments interesting here:


andygere posted 03-02-2005 12:20 PM ET (US)     Profile for andygere  Send Email to andygere     
I'm in the process of reconfiguring the battery system on my Outrage 22 Cuddy. Currently I have dual batteries on a 1-2-Both-Off switch, and a 200 hp main engine (40 amp alternator) and a 15 hp kicker (6 amp alternator), with the house circuit on the common leg of the switch. After reading several good articles on the forum and in the reference section, and brushing up on my 12 volt electrical system knowledge with the "12 Volt Bible", I've decided to install a system like the one jimh describes in this thread. To simplify things, and make for a clean installation in a small space, I ordered a BEP Marine Battery Distribution Cluster, which combines separate on-off switches for the start and house battery, an emergency parallel switch and a voltage sensing relay in one compact package. I paid $145 direct from BEP, which is comparable to buying a stand alone VSR for $75 and 3 compact switches. I haven't installed the system yet, but out of the box I'm impressed. It's well made, compact, and has multiple ports for routing the cables. Also, the folks at BEP answered questions for me over the phone, and were really prompt and helpful. Here's a link to the unit I purchased: I'll post a new thread on the performance of this system once I've installed it and used it for a while.

I'm still undecided on how to wire the kicker to this system. BEP says I can wire it to the start lug of the switch along with the main engine, but I'm concerned that the low alternator output will cause the relay to chatter as Paul notes in this thread. I may simply wire it to the house battery leg of the system, so it will charge only the house battery during trolling, when my electronics (including radar) may run for several hours without current from the big motor's alternator. Any thoughts on this?

One more thing to think about when planning changes to the battery and charging system: don't forget to consider the cost of tinned battery cables, lugs, heat shrink tubing and the like. The Ancor company seems to have a monopoly on these products, and you really pay through the nose for them.

HMBJack posted 03-02-2005 12:50 PM ET (US)     Profile for HMBJack  Send Email to HMBJack     
News Update,

I concur nearly 100% with JimH's assessment.
Here's what I have now:

- two outboards (a 90 & a 5hp)
- two batteries: both are size 24 wet cell, deep cycles.
- two automatic float chargers (1 is 1 amp, the other is .6 amp). I have the luxery of storing my boat in my garage.
- One battery (dual purpose marine) is wired INDEPENDENTLY to my 4 electronics (GPS, VHF, F Finder & Stereo w 2 speakers).
- The other battery is devoted to starting the 90hp and for the rare use of the bilge pump and nav. lights.
- The two batteries SHARE the negative line which is tied to the boat's bonding wire. I think this is a good thing.
- The positive lines however are separate and very independent. Thus, my electronics can't draw off my starter motor.
- The Honda 90 alternator will only charge the starter battery when it is running. The 2nd battery for electronics (70 amp hours) should be plenty for my daily needs and will be re-charged when the boat goes back in the garage at the end of the day.
- If the starter motor fails, there's a good chance the 2nd battery will have enough in it to turn the 90hp Beast.
- In the meantime, both batteries are getting charged 24X7 via the float trickle chargers. So when I splash the boat, both batteries S/B 100%.

Sound like a plan?

GF30 posted 03-05-2005 12:34 AM ET (US)     Profile for GF30  Send Email to GF30     
And if you lose all the battery power, you can still start the engine with a rope, as long as you still have gas!
newportguy posted 03-05-2005 10:31 PM ET (US)     Profile for newportguy  Send Email to newportguy     

I started a 115 Evinrude with a rope so the 90 should start if the flywheel has the notch to hook a rope in. You just wrap it around the flywheel a couple of times and pull. Lift yout cowl and see if your flywheel does not have a place with a groove cut into the wheel.


jimh posted 07-17-2005 06:02 PM ET (US)     Profile for jimh  Send Email to jimh     

Post New Topic  Post Reply
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.