Charging a battery for an electric outboard

[DaveS]

Charging electric outboard battery

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!

There are several ways to go about it, but here's what I do. I've had an electric outboard for a few years and, accepting its limitations, find it Ok.

My approach for the battery was to get an additional 85 Ah "leisure" battery and put it in a plastic box fitted with a tape "basket" to allow easy slinging. This normally lives in a cockpit locker (strapped down) and is connected to a polarised socket. On the dinghy the outboard plugs into this socket; on the boat another plug goes into it. The cable from this plug is connected via a circuit breaker at each end to the 110 Ah domestic battery so that in effect the domestic battery is now bigger, being a bank of two, one of which can be easily detached to power the dinghy.

After using it for a longish run on the dinghy I generally don't close the connecting breakers until the main domestic battery has taken a good charge. I don't have wind or solar generation, but do have shore power, but the principle is the same.

 

[aquaplane]

I'm a frugal user of power and don't have access to 240V so I'm carefull as I suspect you are.

If your ships batteries are doing OK with what you are doing with them now I would be tempted to leave them alone and treat the tender battery as a seperate issue.

So if you are away from the boat for significant periods and only use the tender battery lightly, stick the solar pannel on it to charge it up while you are away.
If you are on a 2 week or longer cruise, monitor the tender battery and get the oars out if it looks like it's not going to last, seemples.

Think what you would do if we were forced back into the dark ages. You don't have to do it, but it's worth thinking about.

 

[Boh999]

Mighty interesting thread! I want to do something similar, but charge the dinghy battery with the house bank WITHOUT starting the sailboat engine. I got a lot of Ah and Solar Panels so in the middle of the day, why not use the surplus to charge the dinghy electrical outboard 48v LiFePO4 battery?

Having read up a bit, it seems 220v to 48v LiFePO4 charger is the way to go, i.e. go via the inverter. Hard to find quality DC-DC chargers that step up from 12v to 48v etc.

Why not...what size charger should I opt for? 50A? Or less? It'd be nice to be able to charge the dinghy battery rapidly, to get going again!

Cheers

 

[William_H]

OP has a 12v outboard. He wants to be able to recharge the 12v battery used for the o/b DaveS seems to have a solution.
However you need 14volts to recharge a 12v battery in a decent time. Current into the battery is a function of the difference between the charging source and the battery being charged. Hence if he connects the o/b battery in parallel with the ships battery a charge current will flow diminishing as the o/b battery is charged. If the o/b battery is very low in voltage a high current will flow. This can be limited by the suggested resistor. A good safety feature which will not waste much power or limit current much in practice.
If however the ships battery is being charged by solar wind or engine then voltage will rise so also getting more into the o/b battery. Hence the only realistic way to charge the o/b battery to any decent degree in a reasonable time is to have the ships system being charged. Note here that a VSR is just an automatic way of connecting the o/b battery to the ships system only when the ships battery is being charged and up to voltage. Not always the case under just solar or wind recharge.
The battery to battery charger would seem like the answer to decant charge from one battery to another quite fast. However I think you will find they are set up with an internal VSR so only charge when the source is above 13.7 volts or so.
So one last option something like this https://www.ebay.com/itm/400W-DC-DC-Step-up-Boost-Voltage-Converter-Constant-Current might be useful. This will step up the voltage of your ships battery even if not being charged from the nominal 12v up to 14volts which will charge the o/b battery. I would suggest fit an amp meter in the charge side to confirm actual charge current. Be aware of course that this could discharge your ships battery in charging the o/b battery. But it can be done without running the engine or having significant solar or wind charging. ol'will

 

[Plum]

However I think you will find they are set up with an internal VSR so only charge when the source is above 13.7 volts or so.
So one last option something like this https://www.ebay.com/itm/400W-DC-DC-Step-up-Boost-Voltage-Converter-Constant-Current might be useful

Thanks but that link does not work for me

Www.solocoastalsailing.co.uk

 

[Boathook]

I use an earlier version of one of these for my bowthruster / windlass battery.
https://adverc.co.uk/products/dc-dc-chargers
Been in place for many years with no problems (last famous words) ......

 

[Red Panda]

I'm very interested in this idea, as it's something I've been thinking about for my own boat when I treat myself to an electric outboard, and I'd to ensure this winter's upgrades prepare for it.
I haven't properly worked through the plan yet, but my general idea would be to use some sort of DC-DC charger to a charging cradle for the outboard battery.
Options I'll look at will include a 3-output Victron ArgoFet for alternator -> engine start, house and outboard.
I already have 20W solar trickle charging that keeps my 110 Ah house + 75 Ah engine start battery at 100% when on the mooring.
My additional 100W of solar is getting permanently mounted this winter, that's surplus energy when on the mooring so might as well get routed to an outboard battery.

I'll have a better think about this later and see if I can come up with a properly calculated solution.

 

[PaulRainbow]

OP has a 12v outboard. He wants to be able to recharge the 12v battery used for the o/b DaveS seems to have a solution.

I suspect that the OP has sorted his charging out, the thread is 9 years old.

 

[PaulRainbow]

Mighty interesting thread! I want to do something similar, but charge the dinghy battery with the house bank WITHOUT starting the sailboat engine. I got a lot of Ah and Solar Panels so in the middle of the day, why not use the surplus to charge the dinghy electrical outboard 48v LiFePO4 battery?

Having read up a bit, it seems 220v to 48v LiFePO4 charger is the way to go, i.e. go via the inverter. Hard to find quality DC-DC chargers that step up from 12v to 48v etc.

Why not...what size charger should I opt for? 50A? Or less? It'd be nice to be able to charge the dinghy battery rapidly, to get going again!

Cheers

A new thread would have been better, your needs are totally different to the original thread, which is 9 years old.

It's already confused people.

 

[AntarcticPilot]

I suspect that the OP has sorted his charging out, the thread is 9 years old.

A new thread would have been better, your needs are totally different to the original thread, which is 9 years old.

It's already confused people.

Indeed, and I sorted out my requirements by selling the electric outboard and buying a Seagull!

 

[PaulRainbow]

Indeed, and I sorted out my requirements by selling the electric outboard and buying a Seagull!

Interesting fix, i'm surprised more people didn't suggest that

 

[lw395]

Interesting fix, i'm surprised more people didn't suggest that

It's only slightly less ridiculous than buying a pair of oars and rowing around in circles letting the freewheeling prop recharge the battery...

 

[RupertW]

Well it’s an old thread but I think it’s now well understood that the simplest practical way to charge the outboard battery is from the house bank. For example with a modest 315AH domestic bank I would lose only 45AH (plus inefficiencies) fully charging my Torqueedo battery from flat. And it’s usually just 15AH needed every day or two.

The only question is whether to 12v charge or AC fast charge via an invertor. I choose invertor despite the extra AH loss as speed matters more to me - domestic batteries get to float between 11:30 and 15:00 depending, so I have excess to use before dusk.

 

[PaulRainbow]

Mighty interesting thread! I want to do something similar, but charge the dinghy battery with the house bank WITHOUT starting the sailboat engine. I got a lot of Ah and Solar Panels so in the middle of the day, why not use the surplus to charge the dinghy electrical outboard 48v LiFePO4 battery?

Having read up a bit, it seems 220v to 48v LiFePO4 charger is the way to go, i.e. go via the inverter. Hard to find quality DC-DC chargers that step up from 12v to 48v etc.

Why not...what size charger should I opt for? 50A? Or less? It'd be nice to be able to charge the dinghy battery rapidly, to get going again!

Cheers

What outboard ?

What battery ?

How do you normally charge it ?

 

[PaulRainbow]

Well it’s an old thread but I think it’s now well understood that the simplest practical way to charge the outboard battery is from the house bank.

How would you charge a 48v LiFePO4 from the house bank ?

 

[RupertW]

How would you charge a 48v LiFePO4 from the house bank ?

The same way I described how I charge the 12v one - via an invertor and mains charger.

 

[AntarcticPilot]

It's only slightly less ridiculous than buying a pair of oars and rowing around in circles letting the freewheeling prop recharge the battery...

Well, the Seagull (a Forty Featherweight Minus) is only slightly heavier than the electric outboard it replaces, is lighter than the battery required for the electric outboard, and is ideal for low speed applications (my dinghy is not capable of planing). The fuel is readily available, and despite all the nay-sayers, Seagulls are extremely reliable once you know their ways. I grew up with them, and my brother and I stripped and rebuilt two while in our middle teens. Anything that can stand that sort of treatment and still work has to be worth some respect!

PS, it also only cost £60!

PPS, I forgot to say that my Seagull is only slightly younger than I am, but it appears to have had a factory refurbishment.

 

[PaulRainbow]

The same way I described how I charge the 12v one - via an invertor and mains charger.

Apologies, missed the bit about the inverter :nonchalance:

That'd be my suggestion, Torqeedo sell a 48v charger, it's only £700 :ambivalence:

 

[William_H]

Appologies I did not notice how old this thread was. The boost converter referred to from Ebay is at
https://www.ebay.com/itm/400W-DC-DC...=183843982240e8261f7c5b5f426ebb5388a963f6540b
Hopefully that will work as a link. They calim it will give up to 60v output so shopuld charge a 48v LiFe battery. However be very carefull charging LiFe abttery as they usaully need a specialised charger as over charrge can be disastrous. ol'will

 

[PaulRainbow]

Appologies I did not notice how old this thread was. The boost converter referred to from Ebay is at
https://www.ebay.com/itm/400W-DC-DC...=183843982240e8261f7c5b5f426ebb5388a963f6540b
Hopefully that will work as a link. They calim it will give up to 60v output so shopuld charge a 48v LiFe battery. However be very carefull charging LiFe abttery as they usaully need a specialised charger as over charrge can be disastrous. ol'will

Connecting a 48v LiFePO4 to a 48v power supply would be very foolish.