Alternator output at slow speeds

P

pcg

Member
I'm doing an energy audit for my C-Dory restoration project and I have two questions...

1) How many amps of charging current (to charge the house battery) can I expect to get from an outboard motor alternator when cruising at the optimum speed for high mpg, which I assume would be hull speed or less? I know this will vary with different outboards so I'm especially interested in those outboards with beefy alternators (i.e Honda BF90 and others).

2) Do any outboard motors have thermally regulated voltage regulators? In other words will they limit current to prevent overheating?

This boat will primarily be used for boondocking and wildlife viewing, so once we get to our destination we plan to putter around for days on end at slow speeds. I will have solar as well, but I'm specifically interested in what I can get from the alternator at slow speeds.

Thank you.
 
I think your best bet is to check the particular outboards specifications. Different outboards with different alternators will have different outputs. I'm guessing most larger outboards will put out anywhere from 30-60 amps at WOT. The smaller kicker motors are more likely in the 10 amp or less range, assuming they have an alternator.
 
I've checked the specifications and they don't specify alternator output at specific RPM. For example, the Honda BF90 alternator has 40A available for charging, but I assume that's at WOT.
What I'm asking for is for information about alternator capability at slow speeds. Surely someone has experience with this.
 
pcg,
This may or not be useful to you, but on my boat (twin 2003 40's) when idling in gear with one engine my voltage at my electronics is about 12.3v. I assume this means my electronics are consuming more energy than my engine is putting out and my battery is actually draining slowly at low rpms.
You may have better luck with a newer and larger motor, but I wouldn't count on getting much charge at low rpms.
 
There are none of the outboards in the range we may be using which will be thermo regulated. (You have to go to speciality alternators / regulators like the Balamar or Leiee Neville--used on Fire engines. or ambulances etc for that type of sophistication.

Having said that, I do have a temperature sensor on my LiFePO4 battery bank from the Sterling Battery to battery charger. This would be a waste of resources to use on a FLA or AGM battery.

The I find that most of the outboards at between 1500 and 2000 RPM are putting out fairly close to max rated capacity. So I don't know what you mean by slow speed. 3 knots or 5 knots?

What is your predicted power usage in 24 hours in amp hours? That is where you want to start. Then you want a good monitoring system, and the best batteries you can afford.
 
Thanks for your thoughts everyone. I'm going to plan on getting very little, if any, charge from the alternator while cruising around slowly. That was what I sort of expected, but I was hoping for something different.
thataway":3bj5v4eo said:
I do have a temperature sensor on my LiFePO4 battery bank from the Sterling Battery to battery charger.
Click to expand...
Yes, my BMS will shut off the charger if the LiFePO4 battery bank gets too hot. However, I'm concerned about the temperature of the alternator on the outboard. I plan on using a buck-boost DC-to-DC converter to charge the LiFePO4 bank when underway. It can supply 25A, taking its power from the alternator. I just want to make sure the alternator doesn't get too hot while delivering over 25A charge current for several hours on a hot day. I have no experience with alternators on outboard motors as my outboards never had them. This is new territory for me.

My question involved two scenarios. which I suppose might have been confusing...
1) Cruising slowly - what can I get from the alternator? I'm going to assume nothing.
2) Cruising at high RPM - I know I can get 25A to the house battery bank, but can I do it for long oeriods of time on a hot day without damaging the alternator?
 
thataway":3f0scskr said:
What is your predicted power usage in 24 hours in amp hours?
Click to expand...

This was my question as well. One problem here is - if you have a large deep cycle house battery that has been drawn down to 50% and it is connected to a relatively small and fragile alternator turning at slow rpm - it will be a sponge sucking as many amps from the alt. as it can get and the alt will attempt to oblige but its fan will not be turning fast enough to cool it producing those amp #'s. I say "fragile" because the average alternator is not designed to be a battery charger. They are mostly built to top up the starting battery and provide normal running amps.

Years ago somebody in our local police force got the idea to change the pulleys on patrol cars to allow the alt. to run faster while idling. After replacing several alternators with fried bearings from being over reved at highway speeds they followed Dr. Bob's advise and installed specialty alternators/regulators.

I once hooked up an alternator to a exercise bike to demonstrate how when it was attached to a battery and full fielded very few people could continue peddling it. The average alt. can consume 5hp so even idling your boat around - when you are charging a low battery you will be using more gas from the load placed on your main. You may be better off using a small invertor generator on the swim platform with a good 3 stage charger. Net gas usage may be negligible. When it comes to charging batteries there is no free lunch!

I have lived off grid since 1979 and in the early years amassed a good sized pile of burnt out alternators :P :P

Regards

Rob
 
Robert H. Wilkinson":3qtuxa6a said:
thataway":3qtuxa6a said:
What is your predicted power usage in 24 hours in amp hours?
Click to expand...
This was my question as well.
Click to expand...
As I mentioned in my first post, I'm in the process of doing an energy audit. I know my predicted energy usage - worst case is 125 Ah. But that's not germane to the question I posted because I already know that. It's the unknowns I need to get answered. ;)

Once daily energy requirements are known, the planning of a system like this is really a balancing act of trying to determine house battery capacity vs. available charging sources, such as solar when it's available, shore power when it's available, generator (which I have, but dislike using), and the alternator. Planning for days of no sun means a bigger battery bank, unless I can get some energy from the alternator while cruising at slow speed. Hence my question. Of course I always have the option of charging from the alternator at high RPMs. I just want to completely understand all scenarios and what's possible. Its all part of the design process.

There are two reasons I chose a C-Dory - 1) It seems to ideally fit our need for a pocket cruiser we can use for boondocking, and 2) this amazing group. Honestly, the value of being able to tap into the resources on this forum is priceless. Thank you all for taking the time to share your knowledge and experience. I need it and very much appreciate it! :)
 
What li FePO4 batteries do you have? (Brand, capacity)

What outboard do you have? (Brand, year and HP)

Why the Buck Booster rather than Victron Orion, which comes in 30 or 18 amps. How do you have the profile of the BB set?

Yes, many of the older, and some smaller outboards use the Stator, Larger have been using alternators for some time.

You can easily put a temperature transducer on the alternator case, and either use a relay to cut off the voltage to converter or an alarm system.

I have snap disc thermostats/contactors on my cooling fans for the batteries and inverter.

I found out the hard way--had a 4 hp motor hooked up to drive a 150 amp alternator belt drive. Could not start the motor. Put a variable field current on, and then started and brought the load up to what I needed. Still there are easier and better ways.

I ended up with a second belt drive off my 10 hp Yanmar generator engine--and the variable field, so I could taylor the load for the DC vs the AC (amps measured draw on my control panel. All was manual, but it worked for 4 years of cruising. I also had a 150 amp alternator on the Main engine (90 HP, that had a "smart" regulator [for its day], and we ran it all of the time, but had a blower in the engine room to keep things cool.)
 
thataway":2ytdsr4s said:
What li FePO4 batteries do you have? (Brand, capacity)
What outboard do you have? (Brand, year and HP)
Click to expand...

I have none of these yet. All I have is literally a bare boat. (See my photo album.) I'm just in the planning stage at this time. I have fiberglass work to do, but want to plan the electrical first. So I'm free to pick the components that make the most sense for my use, as well as a new outboard that makes the most sense.

Re. batteries... At some point I will need to decide whether to get a separate BMS which will give me more choices in Li batteries, or go with something like Victron's Lithium SuperPak which has a BMS built-in, including high temp shutoff. I like the idea of simplifying the design and using the SuperPak as it's one less item (BMS) that I don't have to find room for as space is tight as it is. Do you have an opinion on this?

thataway":2ytdsr4s said:
Why the Buck Booster rather than Victron Orion, which comes in 30 or 18 amps.
Click to expand...
Thank you for that suggestion Bob! I like that product, especially the Bluetooth capability, which I have found very useful (I have he Victron BMV-712 in my camper.).

thataway":2ytdsr4s said:
You can easily put a temperature transducer on the alternator case, and either use a relay to cut off the voltage to converter or an alarm system.
Click to expand...
Yes. It would be nice if I didn't have to do that though.

thataway":2ytdsr4s said:
I have snap disc thermostats/contactors on my cooling fans for the batteries and inverter.
Click to expand...
One thing I'm struggling with now is where to put this stuff so that it can cool via the ambient air. I really don't want to add fans. Trying to keep things as clean and simple as possible. [/quote]
 
thataway":ve8p858t said:
What li FePO4 batteries do you have? (Brand, capacity)
What outboard do you have? (Brand, year and HP)
Click to expand...
I have none of these yet. All I have is literally a bare boat. (See my photo album.) I'm just in the planning stage at this time. I have fiberglass work to do, but want to plan the electrical first. So I'm free to pick the components that make the most sense for my use, as well as a new outboard that makes the most sense.

Re. batteries... At some point I will need to decide whether to get a separate BMS which will give me more choices in Li batteries, or go with something like Victron's Lithium SuperPak which has a BMS built-in, including high temp shutoff. I like the idea of simplifying the design and using the SuperPak as it's one less item (BMS) that I don't have to find room for as space is tight as it is. Do you have an opinion on this?

thataway":ve8p858t said:
Why the Buck Booster rather than Victron Orion, which comes in 30 or 18 amps.
Click to expand...
Because I don't know any better. Thank you for that suggestion Bob! I'm still on a Victron learning curve. I like that product, especially the Bluetooth capability, which I've found very useful. I have the Victron BMV-712 in my camper.

thataway":ve8p858t said:
You can easily put a temperature transducer on the alternator case, and either use a relay to cut off the voltage to converter or an alarm system.
Click to expand...
Yes. It would be nice if I didn't have to do that though. Trying to keep it as simple as possible, but I do want to be able to goose the LI batteries with the alternator if I need to.

thataway":ve8p858t said:
I have snap disc thermostats/contactors on my cooling fans for the batteries and inverter.
Click to expand...
One thing I'm struggling with now is where to put this stuff so that it can cool via the ambient air. I really don't want to add fans. Trying to keep things as clean and simple as possible. On the other hand, perhaps the addition of a fan(s) would allow me to put some of this stuff under the berth area, where I've removed the foam. It it's all Bluetooth it can be out of sight and I can monitor it with a remote device, and I can sure use the space. The battery for sure will be there. Any opinion on this?

Thank you Bob!
 
This 30-minute limit on editing is...not a good idea. I'm active on several other Internet forums and have never seen a restriction like this. I normally use preview a lot, but sometimes I hit submit and don't realize it until later. Really, a one hour limit would accomplish whatever the 30-limit thing is supposed to accomplish I think and would result in less stuff like the above. I had no idea there were two versions and now I can't delete one.
 
Ha! That's true. I was referring to the non-alternator charging systems that are under the flywheel on many outboards. I don't know what year the Honda 90 in question is, but I really thought the early non-EFI ones didn't have an actual alternator. Does this matter? No, and yes. My experience with the earth magnetics and a stator system under the flywheel means they don't make very much power until a lot of RPMs are attained - like at least 3500. Alternators on the other hand, can make a ton of power even near idle speeds, which I concede is often a product of a pulley. Anyway....that's why I brought it up.
 
So from hondas web site my 225 makes 90 amp and my 15 kicker makes 12 amp. I fish on both depending on the current and conditions. I run 2 electric downriggers that are always moving up and down plus all the other electrical stuff most have and I have no problem with the 3 batteries on board staying charged when trolling for 6 hours at idle. I do not think that the rpm has anything to do with output and i have never noticed any heating problems after a 8 hour run at wot. But if you really need to know break out the volt meter and find out.

What motors do you have?
 
Well I just sent this question to honda corp help desk. lets see what they say. never hurt to ask the people that build them.

MODEL 225
SERIAL NUMBER
HOW CAN WE HELP YOU? My motor is rated to produce 90 amp, 60 for charging, is that at idle or wot?
TITLE* Mr.
FIRST NAME Tom
LAST NAME Elliott
EMAIL ADDRESS tom.elliott.fish@gmail.com
PHONE 4252206567
ADDRESS LINE 1 724 118th St Ne
ADDRESS LINE 2
CITY Marysville
STATE WA
ZIP CODE 98271
 
And I just remembered that I have ran all my battery's down once on my 22 and once on the 27, both times I pull started my kicker and recharged the batteries while idling. So there is enough out put to charge 2 dead batteries while at idle. Hope this helps
 
Pcg: I have 2 battleborn 100 amp hrs each. A Sterling 30 amp battery to battery charger. I have the Victron multiples 2000/80/50 inverter charger. I have a 10 amp dedicated Li battery charger (Chinese, monitors amps in & voltage. I monitor with victron 702 (would use 712 if doing today.)

Before I started on the Li path I followed the use in an RV got 10 years. Plus I read a lot. RV, boating, & off grid forums. The technology is changing. New products & sources of information are posted almost daily.

My Honda 150 puts out about 44 amps. I don’t want to use more than 30 amps. I have not been monitoring regularly, except that I have been close to 100 % S O G each evening.

Output of batteries fused at 350 amps. Location of batteries: under port side of The V berth.I cut 3” vent ports & snap discs at 100* f. Computer muffin fans. The inverter charger is on other side. Cables less than 4 ft. 2/00. 500 amp switch.
 
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