Charging a battery for an electric outboard

[AntarcticPilot]

Dear All,

Having recently bought an electric outboard, I am now looking into ways of recharging the battery for the outboard. As one of the reasons I got an electric outboard was to avoid having additional fuels on board, I don't want to consider small generators, though that is one obvious (and cheap) solution. Ideally, I want to be able to charge the battery from the 12 volt cigarette lighter outlet (obviously, with the engine running). Equally ideally, I would like to be able to monitor the state of charge of the battery (a 70 Ah leisure type battery).

I don't use shore power. We have a Rutland 913 charging the two main batteries, but the regulator (HRDi) is only suitable for use with two batteries.

While we are away from the boat, I have a small solar panel that should trickle charge the battery, but this is a low amperage job that will take many days to replace the power used in a short outing with the outboard.

Suggestions welcome!

 

[fireball]

Well - with the Rutland already in place wouldn't it be simplest to just get a replacement regulator that will charge 3 batteries?

Alternative could be - put a switch in the output from one of the outputs so it puts the volts to a socket you can plug the EO battery into (eg the engine battery if you have a dedicated one) ...

 

[AntarcticPilot]

Well - with the Rutland already in place wouldn't it be simplest to just get a replacement regulator that will charge 3 batteries?

Alternative could be - put a switch in the output from one of the outputs so it puts the volts to a socket you can plug the EO battery into (eg the engine battery if you have a dedicated one) ...

Sorry - didn't make it clear that part of the spec is to be able to charge when the wind isn't blowing - the Rutland needs 10-15 knots wind to charge. The information about the Rutland was really to make it clear that the "main" battery bank is normally well charged.

 

[pvb]

Sorry - didn't make it clear that part of the spec is to be able to charge when the wind isn't blowing...

Seems your only choice then is a bigger solar panel, or to charge it by running the engine. Do you have a smart regulator? You should also charge the outboard battery through proper terminal connectors - don't rely on a cigarette lighter socket.

 

[fireball]

well - why didn't you say so?!

What charging equip do you have from your engine altenator? Is it split diode or a smart charger? Simplest option would be to put a smart charger in with 3 outputs (incase the rutland breaks down!) and then plug the OB into that (as PVB says - don't do a Cig Socket - choose something a bit more robust please!!)

 

[VicS]

As pvb says don't use a cigarette lighter socket. They are OK for cigarette lighters that clip in firmly but make poor and unreliable contact with the plugs normally available to fit them.
The result can be overheating, even melting, of the plug, possible damage and even shorting of the wiring esp when used for what might be quite a high current connection.

There are some decent similar type of sockets available in which the plug locks into the socket. Use one of those at least, otherwise a decent conventional plug and socket that will withstand the maximum charging current that is likely.

I was wondering if a VSR could be used to charge from one of the existing battery circuits. It would automatically close to charge your outboard battery when the engine is running or when there is sufficient output from the Rutland but would automatically open again when the engine is stopped and the Rutland is not charging.

The trouble with electric outboards is that you have to recharge the battery! With a small petrol engined one you just refill its tank.

 

[AntarcticPilot]

As pvb says don't use a cigarette lighter socket. They are OK for cigarette lighters that clip in firmly but make poor and unreliable contact with the plugs normally available to fit them.
The result can be overheating, even melting, of the plug, possible damage and even shorting of the wiring esp when used for what might be quite a high current connection.

There are some decent similar type of sockets available in which the plug locks into the socket. Use one of those at least, otherwise a decent conventional plug and socket that will withstand the maximum charging current that is likely.

I was wondering if a VSR could be used to charge from one of the existing battery circuits. It would automatically close to charge your outboard battery when the engine is running or when there is sufficient output from the Rutland but would automatically open again when the engine is stopped and the Rutland is not charging.

The trouble with electric outboards is that you have to recharge the battery! With a small petrol engined one you just refill its tank.

First, what is a VSR? Sorry to be thick, but I'm afraid this is fairly new territory for me. I'm OK with A-level physics kind of electrics - Ohm's and Kirchoff's Laws and their ramifications, but this is too specialized for me. I was very surprised to find that there wasn't an off-the-shelf solution for this one - it seems to be such an obvious thing to want to do!

I had considered the recharging angle; I just hadn't realized it would be tricky, especially with a boat whose electrics are about 20 years old. Everything works, but by today's standards it is a little primitive, and as it all works, I have no wish to try and upgrade it.

And yes, petrol outboards can just be refuelled, but they are unwieldy objects that leak petrol if mis-handled. They are also heavy, with the weight in a single lump. Finally, they are noisy! The electric outboard scored on weight, cleanliness, simplicity and quietness. There is also the issue of multiple fuels aboard.

 

[stevesales]

What capacity are your 'house' batteries?

 

[VicS]

A VSR is a voltage sensitive relay. They are commonly used for charging two or more batteries from a single source rather than diode splitters because they do not suffer from the volts drop which you get across diodes.

They remain open until the volts have risen to 13.7, thereby allowing the normal battery ( engine start perhaps) to recharge at least partially then they close to connect the auxiliary battery. They open again if/when the volts drop back to normal level.

 

[Evadne]

I had considered the recharging angle; I just hadn't realized it would be tricky, especially with a boat whose electrics are about 20 years old. Everything works, but by today's standards it is a little primitive, and as it all works, I have no wish to try and upgrade it.

And yes, petrol outboards can just be refuelled, but they are unwieldy objects that leak petrol if mis-handled. They are also heavy, with the weight in a single lump. Finally, they are noisy! The electric outboard scored on weight, cleanliness, simplicity and quietness. There is also the issue of multiple fuels aboard.

Don't worry, you're not alone, I use an electric o/b for getting up and down the creek to the mooring for the reasons you state. Charging is done at home, so I'm of no help there sadly, I presume you're talking about what to do on extended trips, other than using the oars, when avoiding marinas. For recharging over a weekend you'd be looking at a fairly quick mains charger anyway, a generator (or fuel cell) or running the engine for several hours. A spare battery would be more convenient than those IMO.

 

[AntarcticPilot]

What capacity are your 'house' batteries?

110 Ah for both engine and house batteries. However, they would NOT be the charging source for the outboard battery; indeed, it sounds like a VSR is the way to go as suggested elsewhere.

 

[stevesales]

You'd half discharge the house battery then if you just bung the motor battery across it with a current limiting resistor without running the engine. 2 ohms will give 6A charge so you'd need a 15 watt resistor. I can't see any reason why this won't work with the engine running as well since the house battery will see a controlled charge voltage. You'll loose 12W into the resistor but that's nothing. However do complicate things if needed. That's what boats are for after all!

 

[AntarcticPilot]

You'd half discharge the house battery then if you just bung the motor battery across it with a current limiting resistor without running the engine. 2 ohms will give 6A charge so you'd need a 15 watt resistor. I can't see any reason why this won't work with the engine running as well since the house battery will see a controlled charge voltage. You'll loose 12W into the resistor but that's nothing. However do complicate things if needed. That's what boats are for after all!

I wouldn't attempt to charge it from the house battery without running the engine - of course, I would simply flatten the house battery.

 

[stevesales]

I explained that you wouldn't. You'd still have 35 Ah left without running the engine (actually more because the house battery voltage would fall off during transfer of energy to the other battery). It would take 12 hours to charge and I imagine you'd be running the boat engine during this time.

 

[VicS]

If fancy electronc wizardry floats your boat ... I suspect it doesn't ..... you could consider one of Charles Sterlings battery to battery chargers.
It will do what a VSR will do but it will also optimise the charging and extract the maximum from the alternator.

Not sure if it would work with the Rutland ... you would have to ask Mr Sterling it it is not clear in the on-line literature... and stand by for one of his one word answers

See http://www.sterling-power.com/products-battbatt.htm

 

[AntarcticPilot]

If fancy electronc wizardry floats your boat ... I suspect it doesn't ..... you could consider one of Charles Sterlings battery to battery chargers.
It will do what a VSR will do but it will also optimise the charging and extract the maximum from the alternator.

Not sure if it would work with the Rutland ... you would have to ask Mr Sterling it it is not clear in the on-line literature... and stand by for one of his one word answers

See http://www.sterling-power.com/products-battbatt.htm

Well. they look like a good product - but for me, the price is way too high. That's more than I have paid for outboard and battery so far!

 

[Fantasie 19]

Is taking the battery home to charge not an option???

 

[Graham_Wright]

Don't outboards have built-in alternators?

 

[VicS]

Don't outboards have built-in alternators?

The electric ones don't ... but what a good idea fit a big alternator and then it'll charge its own battery as it goes.

 

[MonniotC]

I think you will eventually realise that electric outboards are not practical as motors for yacht tenders because of the problems associated with battery charging, particularly if you don't have regular access to shore power. I have one in the corner of my garage. Flover 33s used twice. I'm open to offers.