On board charging for a 12v Trolling Motor Battery - No shore power

[Moonbeam]

I have recently purchased a Bison 68 that I'm currently using with an old 12v 70Ah lead acid starter battery. But, I'm considering buying a 12v 100Ah LiFePO4 battery to use instead. But either way, I need to be able to charge the 12V battery on board when away from shore power as most time is spent at anchor for several days at a time.

I have a CTEK MXS 5 amp mains powered battery charger that I had hoped would work off my humble Maplins 150w inverter. But it does not (Inverter alarm goes off). So... I'm now in need of a decent charging solution.

The boat set up is 2 x Varta LFD 140 (280Ah total) 12V house bank that, when anchored, is charged via a single 260 watt solar panel via a Victron smart MPPT 100/20 charger. The main demands from that battery bank are a 110 litre 12V fridge running 24/7 plus other minor demands like fresh water pump, electric toilet, etc. By the morning the house battery bank is down to about 91% according the the Victron BMV-700. The solar usually has it back to 98% by about midday and in float/100% by about 2pm, but can be later if weather is dull or panel in shade etc.

What are my best options? From my research, they seem to be

1: A larger inverter (size?) to use mains chargers.

2: DC to DC battery charger, like an Victron Orion 12/12 18?

3: Some kind of switch to channel the Victron Smart solar charger to divert charging to another battery?

4: Something I've not thought of...

Considerations are: Keep costs low, and the trolling battery to be charged will need to sit in a removable and accessible location, being plugged in and out of the charging system easily (harness with Anderson plugs?)

The Victron Orion seems designed to work from the alternator/start battery set up rather than just a house battery bank to another battery. Is the Orion feasible?

Do I even have enough capacity in the house bank for this whole idea? Or do I need to get my dreaded petrol outboard up and running again!

Would love an epropulsion, but too pricey.

 

[rogerthebodger]

I am currently setting up a similar setup and I am using a 30-watt solar panel to charge my LiFePO4 battery

 

[Boathook]

I have recently purchased a Bison 68 that I'm currently using with an old 12v 70Ah lead acid starter battery. But, I'm considering buying a 12v 100Ah LiFePO4 battery to use instead. But either way, I need to be able to charge the 12V battery on board when away from shore power as most time is spent at anchor for several days at a time.

I have a CTEK MXS 5 amp mains powered battery charger that I had hoped would work off my humble Maplins 150w inverter. But it does not (Inverter alarm goes off). So... I'm now in need of a decent charging solution.

The boat set up is 2 x Varta LFD 140 (280Ah total) 12V house bank that, when anchored, is charged via a single 260 watt solar panel via a Victron smart MPPT 100/20 charger. The main demands from that battery bank are a 110 litre 12V fridge running 24/7 plus other minor demands like fresh water pump, electric toilet, etc. By the morning the house battery bank is down to about 91% according the the Victron BMV-700. The solar usually has it back to 98% by about midday and in float/100% by about 2pm, but can be later if weather is dull or panel in shade etc.

What are my best options? From my research, they seem to be

1: A larger inverter (size?) to use mains chargers.

2: DC to DC battery charger, like an Victron Orion 12/12 18?

3: Some kind of switch to channel the Victron Smart solar charger to divert charging to another battery?

4: Something I've not thought of...

Considerations are: Keep costs low, and the trolling battery to be charged will need to sit in a removable and accessible location, being plugged in and out of the charging system easily (harness with Anderson plugs?)

The Victron Orion seems designed to work from the alternator/start battery set up rather than just a house battery bank to another battery. Is the Orion feasible?

Do I even have enough capacity in the house bank for this whole idea? Or do I need to get my dreaded petrol outboard up and running again!

Would love an epropulsion, but too pricey.

I would go the dc to dc battery charger. A good one won't drain the main battery bank as it will shut down. I've got an adverc? one to charge my bow thruster battery.

 

[ylop]

But either way, I need to be able to charge the 12V battery on board when away from shore power as most time is spent at anchor for several days at a time.

How often does it need charged? Your proposed Li option would give you close to 3x the range… have you considered just getting two of those and charging on shore power either at home or marina from time to time? Roger’s suggestion of a dedicated 30W panel might top up a short trip ashore over the course of a day?

Considerations are: Keep costs low, and the trolling battery to be charged will need to sit in a removable and accessible location, being plugged in and out of the charging system easily (harness with Anderson plugs?)

By the time you buy a lipo (or two!) and the various bits of wiring water proof connectors, ways to secure it etc, you probably are about half way to the cheaper “proper” electric outboard options?

 

[Alex_Blackwood]

I am currently setting up a similar setup and I am using a 30-watt solar panel to charge my LiFePO4 battery

+1 Solar panel even if portable. Rig it up when you leave the boat and stow on return. You will want a half decent controller if not a very small panel.

 

[B27]

Firstly, you should check that the LifePO4 battery will actually power the Bison.
Many have current limits around '0.5C' which means your 100Ah battery might be limited to 50A.
What does the Bison actually draw as an inrush current?

Secondly you need to ask how much power you need for how long , how often.

I've been thinking about this myself and I reckon for a typical cruise of a few days around the Devon or Cornwall coast, I might want anything up to an hour's outboard use in a day, I could possibly have a few days of that with no engine charging
If that was all at full current then that's a lot of amp-hours.
So it would be good to gather some actual data of Ah used by the Bison in real life conditions.

If your solar is typically charging 280Ah of batteries from 90% to 100% by midday, you could say that's about 28Ah in the morning, and extrapolate that you've got another 28Ah or a bit more available in the afternoon?

So if you were simply to divert the solar to the lithium battery would that yield enough for your outboard use?
On the face of it, it looks like it probably would.
But how resilient to dull days and shorter days later in the season do you want to be?
Can you afford to accept that sometimes the outboard battery won't get charged?
I probably can, if it has enough capacity for say 3 days typical use.

My boat is a weekender really, so I'm happy to come home after a few days then leave it mooring where the solar panel(s) will sort things out before I next go sailing. I only have 50W of fixed panel and another 60W of 'temporary' to plug in.

But I'd also like the flexibility of being able to charge everything from the engine alternator, which is probably most simply done using a B to B charger or DC-DC converter. To get any useful charge from the way I tend to use my engine, I'd prefer to be looking at 20A or more of B to B.

The thing is, I feel that once I switch to an electric outboard, I will be a bit committed.
At the moment I can rely on my Yamaha, it worked yesterday, so I'm pretty confident it will work tomorrow.
If I don't use it for a month, I would not be surprised if it needed a carb clean next time I wanted it.

 

[B27]

+1 Solar panel even if portable. Rig it up when you leave the boat and stow on return. You will want a half decent controller if not a very small panel.

Something like a 30W solar panel will yield something like 10Ah on a fairly good day?
How much outboard run time is that?
Then of course if you spend a chunk of the sunny part of the day ashore with the tender, you're losing a lot of photons!

There's a huge difference between solutions which work every day in all weather and things which work part time on a good day.

 

[Boathook]

The thing is, I feel that once I switch to an electric outboard, I will be a bit committed.
At the moment I can rely on my Yamaha, it worked yesterday, so I'm pretty confident it will work tomorrow.
If I don't use it for a month, I would not be surprised if it needed a carb clean next time I wanted it.

I didn't use my malta for nearly a year and it started 4th pull. The petrol was e5 and I had dosed it with an enzyme additive plus also running the malta after the fuel tap was turned of. Might have saved me buying an epropulsion if i had done this a few years ago !

 

[B27]

I didn't use my malta for nearly a year and it started 4th pull. The petrol was e5 and I had dosed it with an enzyme additive plus also running the malta after the fuel tap was turned of. Might have saved me buying an epropulsion if i had done this a few years ago !

I've been involved with many outboards and many other small engines with carburettors for something over 45 years.
Yes they sometimes start relatively easily after various periods of neglect.
The point is that the probability of not starting easily increases over time.
With an outboard on the sea, I want a very high probability of it starting.

Also a big gain of an electric outboard would be not having to store a petrol engine on a small boat, where it's an awkward, dirty, smelly thief magnet.

 

[B27]

....ay?

By the time you buy a lipo (or two!) and the various bits of wiring water proof connectors, ways to secure it etc, you probably are about half way to the cheaper “proper” electric outboard options?

This line of thought would be more useful with numbers.
100Ah Battery from Eco-Worthy, £220.
Bison, about £160?

Cheapest e-propulsion thing about £1200?

It's possible to reduce the battery cost, but that £220 is a solid, off the shelf solution, delivered in the UK inc VAT.

What batteries do cheaper off the shelf e-outboards have?

 

[Alex_Blackwood]

Something like a 30W solar panel will yield something like 10Ah on a fairly good day?
How much outboard run time is that?
Then of course if you spend a chunk of the sunny part of the day ashore with the tender, you're losing a lot of photons!

There's a huge difference between solutions which work every day in all weather and things which work part time on a good day.

I think he may find that any on board charging setup would be pretty much useless in that case. No?

 

[B27]

I think he may find that any on board charging setup would be pretty much useless in that case. No?

Not at all.
If you have plenty of battery on the yacht, then recharging the outboard using a B-to-B charger in the evening or next day is a solution.

Or simply having a big enough outboard battery to last several days of your anticipated use.

I'm seeing a lot of electric outboards on tenders this year, but I think it's mostly people who just charge them at home.

 

[KompetentKrew]

With a lead acid battery like you're currently using to power the Bison, surely you can just parallel it with the house bank? Use a pair of jump leads.

This will discharge the main bank a bit, but no problem because you're getting it back up o 100% every day, anyway. Maybe it'll take 2 or 3 days to get back up to 100% on the days you need to charge the Bison's battery.

You only need a B2B charger if you use a lithium battery for the Bison because it's a different battery chemistry and you need to be careful not to expose it to too high a voltage ((3.3v per cell??). But if the battery is the sea chemistry as you house bank then your SmartSolar is already calibrated for the right bulk/absorption/float voltage levels.

Not sure what kind of current would be drawn when charging but the spec for the BMV-700 says it handles 1000A anyway (seems like a lot!) so you can monitor how much you're discharging the main bank - just ensure the negative jump lead is connected to the other side of the BMV's shunt, not to the house battery itself.

 

[Moonbeam]

Thanks for the replies chaps.

Purchased the Bison as I finally got fed up almost dislocating my shoulder the last time trying to get the petrol outboard running. Took over 40 pulls to start, then did not run well and then refused to start once we stopped at a beach... it nearly got left there! But it had been in hibernation, so probably to be expected.

Difficult to say what the usage pattern will be for the Bison. But have a pontoon mooring, so it's just for occasional trips to the shore or exploring rivers and creeks. So, fun only.

Bison say it draws 64 amps at full chat. Have only used it once, with the old and retired 70Ah car starter battery. Ran it for approx 40 mins at mostly speed 3, some at 4 and a very short blast at 5 from the 5 speed settings. Once back at the boat, rested the battery before testing it with the Topdon battery tester which claimed it was down to 33% charged, and a 'bad' battery to be junked. But the CTEK recondition charge at home has it back to 'good' and healthy. But that 5 amps charger took all day to get there.

As some have suggested, I'm thinking the separate dedicated solar panel and charger might be a good option seeing as I have the space for it. Might be able to fit a 100w panel. Low cost too. Perhaps just have a second cheap lead acid deep cycle battery. Toggle between the 2.

In the meantime, I went out to the shed this morning to fettle with the petrol outboard. Set it up in the water butt. Put some fresh BP 'Active' 97 Octane E5 petrol in plus some Forte injection cleaner.... It started first pull !!!!!

 

[Sea Change]

I think it would be a very good idea to have a pair of LFP batteries for an electric outboard- one stays behind on charge, and on long expeditions you could bring both.

You can buy supposedly waterproof LFP batteries ready fitted to a pelican type case, with a battery monitor etc, on Alibaba.

I would say, based on a probably above average amount on experience using a Bison 68 with a small portable LFP battery, that the key thing to get right is the connections. I was just using crimped eye terminals which fitted the M8 threads on the battery. Simple, but it was very easy to drop an end in to the bottom of the dinghy, and it doesn't take much saltwater to cause corrosion. It would wick up the strands of the cable, and manifest itself with excess heat when running. Solution was to keep cutting six inches off and fit a new eye. I'm not sure if there's a perfect long term answer- Anderson plugs seem good, but you'd really want something with a sprung cover, like a commando socket.

 

[Sea Change]

need to be careful not to expose it to too high a voltage ((3.3v per cell??).

You can go up to about 3.7v without worrying too much, although it's not great for lifespan. For regular use there's little point going above 3.5v, IMHO.

 

[noelex]

If you have excess solar energy I would not install a dedicated solar panel to charge the LiFePO4 battery. A DC to DC battery charger is the best solution.

 

[Alex_Blackwood]

Not at all.
If you have plenty of battery on the yacht, then recharging the outboard using a B-to-B charger in the evening or next day is a solution.

Or simply having a big enough outboard battery to last several days of your anticipated use.

I'm seeing a lot of electric outboards on tenders this year, but I think it's mostly people who just charge them at home.

Yes to be serious if he wants to charge overnight on board. then B-B. With a small solar panel he could always take it on the tender and have it connected to the battery for charging while he goes off to the pub, sightseeing or shopping, what ever

 

[RupertW]

Not at all.
If you have plenty of battery on the yacht, then recharging the outboard using a B-to-B charger in the evening or next day is a solution.

Or simply having a big enough outboard battery to last several days of your anticipated use.

I'm seeing a lot of electric outboards on tenders this year, but I think it's mostly people who just charge them at home.

We have had an electric outboard for 10 years now and almost always charge it from main domestic battery bank. With 400Ah lead acid batteries and 400W solar, then the typical charge of 500Wh every 3 or 4 days is easy to manage and barely noticeable as we always have excess which is normally used to heat a tank of water once batteries go to float after lunch.

 

[noelex]

The best time to charge the LiFePO4 battery is when the solar output is regulated. The excess power can be used charging the battery instead of being wasted. In this way the power is "free". There is no detrimental effect on the house bank or need for additional dedicated panels.

The OP has indicated that the house bank is usually "98% by about midday and in float/100% by about 2pm". The solar controller is regulating the power for a reasonable portion of the day so there should be enough of time for charging the LiFePO4 battery.