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How much is too much Solar Power and how much is just enough?


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35 minutes ago, DaveP said:

I've had my solar panels occupying the first 3.5m of roof since 2013; the question of ladders did concern me, but it has turned out that very, very, few locks are badly placed.  I now tend to bow-haul the boat (at least partially) in or out as needed.  During the winter months, I have another pair of panels (1.0m x 3.5m) about 2/3 along the boat, again I'll bow-haul the boat to the right place.  These panels are offset to the centreline, so there is a wider shufflepath past them, although it's not the best.

 

Dave

 

 

Cheers Dave, I've never actually hauled the boat into a lock (although only actually been out cruising for a total of about 6 months so far). I've pondered it a few times but it looked too much of a faff, so I just drive in.  

I'm usually not going to realise there is a forward-placed lock ladder until I'm actually in the lock, but if that happens (and I can only remember 2 of them so far) I'll just reverse out and jump ashore with the centre line. and haul as you suggest. 

I feel that the benefits from the extra solar panels are going to be worth a bit of hassle at a few locks. 

There is a back up option anyway- I'm looking at panels a metre wide at the moment, which would actually give just enough width to walk alongside and get forward, if that was my only option. 

I've seen a few debates about tilting, and my current thinking is that a 240 watt panel tilted at the sun will generate more power in winter than a larger (say 400 watt) panel laid horizontal, so I'm looking at panels that are at most about 1 metre wide.

My first priority is to upgrade my engine charging capacity, and the solar will come after that, probably in early Sept.

So the boat should be all finished by October. 

(No, I dont really believe that 😀)

 

 

Edited by Tony1
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Tilting panels don't give that much more power than flat ones, best case is about 15% more -- there are more details on other threads. Whether it's worth all the hassle of tilting mounts is up to each boater to decide, many think it's better to have solidly mounted flat panels.

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4 minutes ago, IanD said:

Tilting panels don't give that much more power than flat ones, best case is about 15% more -- there are more details on other threads. Whether it's worth all the hassle of tilting mounts is up to each boater to decide, many think it's better to have solidly mounted flat panels.

Even worse when you pass someone in the morning and their panels are tilted in the wrong direction because they haven't moved them from the previous afternoon.

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9 minutes ago, IanD said:

Tilting panels don't give that much more power than flat ones, best case is about 15% more -- there are more details on other threads. Whether it's worth all the hassle of tilting mounts is up to each boater to decide, many think it's better to have solidly mounted flat panels.

 

If its definitely only a 15% gain then frankly its not worth the extra hassle of a tilting mount. 

 

But I have seen a number of conflicting reports about the effectiveness of tilting panels. 

 

In this example, a small solar panel that is steeply tilted puts out 0.41 amps, and when laid flat the output drops to 0.15 amps, so the tilting in this case more than doubles the current output. I know very little about solar or electrics, and I could well be missing something important in this demo, but at first glance this does make a compelling demonstration.

So at the moment I am leaning towards using tilting mounts based on seeing these sorts of reports, and from my own much less accurate observations over the last 8 months.

 

I do agree that its certainly a valid question each boater must consider for themselves, and for those with charging systems that can charge at say 100 amps, it might seem trivial and a waste of time to be tilting several large panels several times a day in search of an extra 3 or 4 amps over 8 hours of weak winter daylight, when they can just run their engine and create three or four times the amount of power in 45 minutes.

 

 

 

 

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Angling the panels makes more impact in the winter when the sun is st a low angle but little difference in the summer. However, in the winter even if angling the panels doubles the yield, two times nothing is still nothing. Once averaged over the year, because most solar is harvested in the summer when angling is less effective, the annual impact is low. There s are websites where you can put in location and panel direction and angle and it will give average yields throughout the year so you can check flat and angled.

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1 hour ago, Rob-M said:

Even worse when you pass someone in the morning and their panels are tilted in the wrong direction because they haven't moved them from the previous afternoon.

You don't need to move them during the day, just face them south -- which of course is an issue on a canal unless you can choose to moor where it runs east-west...

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18 hours ago, Tony1 said:

 

Can I ask Peter, how do you get to the lock ladder when singlehanding in locks, when the lock ladder is halfway along the lock?

There don't seem to be many like that, but I've come across a few. 

So far I use the roof to get to the ladder, but that will be difficult or impossible if the roof is full of panels

 

I've heard some people use the gunnels to reach the awkward ladders, but there are a few locks (like Hurleston) where I'm not sure they are wide enough for you to walk along the gunnels. 

 

I have proper gunnels not toy ones like on most narrowboats Tony, remember I have a widebeam so my locks leave plenty of room to walk down the side 

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On 24/07/2021 at 11:01, peterboat said:

I have proper gunnels not toy ones like on most narrowboats Tony, remember I have a widebeam so my locks leave plenty of room to walk down the side 

Assuming you plan to use the standard size mono panels (typically 1.78m long x 1.05m wide) fitted down the middle of the roof, you should have just under a foot down each side to walk along the roof on.

 

https://www.bimblesolar.com/solar/large-panels/380W-JA-solar

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On 23/07/2021 at 22:40, PeterF said:

Angling the panels makes more impact in the winter when the sun is st a low angle but little difference in the summer. However, in the winter even if angling the panels doubles the yield, two times nothing is still nothing. Once averaged over the year, because most solar is harvested in the summer when angling is less effective, the annual impact is low. There s are websites where you can put in location and panel direction and angle and it will give average yields throughout the year so you can check flat and angled.

Which is where the 15% came from -- actually it's 16% if you want to be *really* precise... 😉

 

Also don't forget that 16% is the best-case gain assuming you can tilt the panels facing south, which will often not be possible on a moored boat. If you average over all boat orientations, the gain drops to 8%.

 

My preference would be to get as many high-efficiency panels in as possible (6 x 380W will fit on most boats) and flat-mount them to keep the profile as low as possible, rather than using mounts to allow tilting which also raise them up further and make them look more obtrusive. Flat-mounted panels also have the benefit of being harder to nick, if you worry about that 😉

 

solar panel angle.png

Edited by IanD
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2 hours ago, IanD said:

Which is where the 15% came from -- actually it's 16% if you want to be *really* precise... 😉

 

Also don't forget that 16% is the best-case gain assuming you can tilt the panels facing south, which will often not be possible on a moored boat. If you average over all boat orientations, the gain drops to 8%.

 

My preference would be to get as many high-efficiency panels in as possible (6 x 380W will fit on most boats) and flat-mount them to keep the profile as low as possible, rather than using mounts to allow tilting which also raise them up further and make them look more obtrusive. Flat-mounted panels also have the benefit of being harder to nick, if you worry about that 😉

 

solar panel angle.png

 

Thanks Ian, this is very interesting, and is changing my view on tilting. This looks like its focused on domestic panels in fixed mounting positions on house roofs, and also its an annual chart.

Is there something similar, but just for the winter months?

I'm seeing the winter challenge as a separate thing to the rest of the year, really, in that the sun is usually pretty low.

 

As PeterF says, in summer the sun is much higher in the sky, so in the summer you lose less of your potential power when you lay the panels flat. Hence they still yield 84% of their potential power when flat, during the warmer months. 

But in winter, there might be a case to made for tilting- but ONLY if you can also point them southward, as you said above.

 

I guess the ideal world setup would be a mount that swivels to point south and also tilts to 50 degrees or so- but the cost of that would be very significant.

Without knowing the figures for the power gains when tilting panels in winter, and with the mounts not being too expensive, I'm inclined to get tilting mounts. BUT clearly its only worth using them in winter, and even then only if they are facing roughly south. 

Moorings seem to be a bit more tricky in winter, and I certainly dont want to further limit myself by only mooring in spots where the boat is pointing east of west.  That's not feasible at all, and if I find a nice, open, quiet mooring with a dry-ish towpath and a nice view, I'm not going to ditch it because the boat isnt facing the right compass direction to garner an extra 30Ah during the day. 

I got a distorted view of my panels efficiency last winter because I was in a marina moored with the bow almost due east, so the panels were ideally positioned the while time. 

The same wont be the case next winter, and for half of the time I imagine they'll stay flat.

 

Edited by Tony1
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I did find more detailed analysis elsewhere but I can't remember where -- if you search for "solar panel yield UK" you'll probably find it somewhere in the first couple of pages of results. All year round -- but especially in spring/autumn/winter -- a significant part of the power comes from diffuse light from the sky not direct sunlight, and this is maximum for flat panels.

 

As somebody pointed out earlier, you might get a bigger percentage improvement in winter by tilting (assuming south-facing), but the power is so low then anyway it won't make much difference in absolute terms. Also in winter a bigger part of the power (on average) comes from diffuse light -- so even if you get a (small) increase with tilted panels when the sun is shining, you'll probably lose some when it's not, which is far more common in winter...

 

From aesthetics and security points of view I also think flat panels are better, most of the tilting mounts raise them up significantly even when lying flat.

Edited by IanD
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25 minutes ago, IanD said:

I did find more detailed analysis elsewhere but I can't remember where -- if you search for "solar panel yield UK" you'll probably find it somewhere in the first couple of pages of results.

 

As somebody pointed out earlier, you might get a bigger percentage improvement in winter by tilting (assuming south-facing), but the power is so low then anyway it won't make much difference in absolute terms. Also in winter a bigger part of the power (on average) comes from diffuse light from the sky not direct from the sun, and this is highest for flat panels -- so even if you get a (small) increase with tilted panels when the sun is shining, you'll probably lose some when it's not, which is far more common in winter...

 

From aesthetics and security points of view I also think flat panels are better, most of the tilting mounts raise them up significantly even when lying flat.

 

Thanks Ian- its clear that even in winter, the benefits of tilting panels are not going to be anything like as much as I had initially imagined, especially given how important the compass direction also is. I had approached this issue too simplistically, as usual.

 

I'll try to dig out some winter-specific info before I come to a final decision. 

I have mushroom vents in the places I want to put panels, so I'm planning to replace those with the flatter vents. I also need to grind off the mounting stand things for the plank and the pole, which take up over 2m of roof length at the moment. They can both go indoors I think. 

 

There is one advantage that I do like with flat panels- midsummer energy advertise mountings (for smaller panels) that they say can be glued down, and dont need to be screwed. If I could do that, it would make things a bit simpler, and I do like to idea of fewer holes in the roof.  Another idea I had was to glue flat plywood panels 30cm square onto the roof, and then screw the panel mounting base to the plywood. At least that way there is a larger surface area being held by the glue. 

But one must consider the worst case, i.e. a winter storm with gusts across the roof at 60-70 mph.  

 

https://midsummerenergy.co.uk/buy/solar-panel-mounting/solar_panel_corner_mounts

 

This is the glue they advise using: 

 

https://sunworks.co.uk/product/solar-panel-adhesive/

 

 

 

 

 

Edited by Tony1
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1 minute ago, Tony1 said:

But one must consider the worst case, i.e. a winter storm with gusts across the roof at 60-70 mph.  

I have 4 little Z bracket "feet" on each of my panels, each stuck to the roof with Stixall. It's quite a neat, unobtrusive, low profile solution which still allows cooling airflow under the panels. They've been through everything the British climate has thrown at them and have been totally fine. 

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43 minutes ago, Tony1 said:

 

Thanks Ian- its clear that even in winter, the benefits of tilting panels are not going to be anything like as much as I had initially imagined, especially given how important the compass direction also is. I had approached this issue too simplistically, as usual.

 

I'll try to dig out some winter-specific info before I come to a final decision. 

I have mushroom vents in the places I want to put panels, so I'm planning to replace those with the flatter vents. I also need to grind off the mounting stand things for the plank and the pole, which take up over 2m of roof length at the moment. They can both go indoors I think. 

 

There is one advantage that I do like with flat panels- midsummer energy advertise mountings (for smaller panels) that they say can be glued down, and dont need to be screwed. If I could do that, it would make things a bit simpler, and I do like to idea of fewer holes in the roof.  Another idea I had was to glue flat plywood panels 30cm square onto the roof, and then screw the panel to the plywood. At least that way there is a larger surface area being held by the glue. 

But one must consider the worst case, i.e. a winter storm with gusts across the roof at 60-70 mph.  

 

https://midsummerenergy.co.uk/buy/solar-panel-mounting/solar_panel_corner_mounts

Those mounts are much too feeble for full-size panels like the 380W ones I gave the link to which weigh about 20kg each. You could use the Z-mounts from Midsummer, these need screws through the roof -- but then I'm not sure I'd like to rely on glue to hold down panels that big and heavy in a gale, if the wind gets under them they could turn into lethal giant frisbees... 😞

 

https://midsummerenergy.co.uk/buy/solar-panel-mounting/solar-mounting-feet-100mm

 

Suggest you look at bimblesolar, cheaper high-output panels, much bigger choice of mounting hardware especially for full-size panels -- they have some strip-type mounts designed for the job which should be fine if glued down since they have at least 10x the glue joint area of the Midsummer Z-mounts...

Edited by IanD
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I think its worth pointing out another plus from adding extra solar panels, at least during the summer. 

 

Between say April and Sept, with 1.2kw of solar, even on days with moderate cloud cover I would expect there will always be enough power to run the fridge and most other normal items aboard (as long as you are not totally overshadowed by trees). 

And on most days, there will be more solar power coming in than I can use. 

That means I can fit a solar energy 'dump' system, which will divert excess solar to heat up water, once the batteries are full.

 

This could mean that on even moderately sunny or bright days, I would basically have hot water on tap for most daylight hours, and into the evening- without running the engine. 

At the moment I have to heat a pan/kettle on the cooker, or else run the engine for maybe 40 mins to get hot water- and that all uses either diesel or gas- and that's happening every day.

 

Now it must be said that if you are a person who cruises every other day in the summer, then hot water is not such an issue, as you'll be running the engine a fair bit anyway.

But in my case I do often like to moor for 3 or 4 days at a time, and have a good look around the local town or village- and it would be great to have hot water available for a lot of the day without me running the engine/cooker. 

 

So although the benefits of extra solar start to become a bit more marginal from say Nov to Feb, there are definite benefits in terms of hot water between say May- Sept, at least for someone with my sort of cruising pattern.

 

 

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4 hours ago, IanD said:

Those mounts are much too feeble for full-size panels like the 380W ones I gave the link to which weigh about 20kg each. You could use the Z-mounts from Midsummer, these need screws through the roof -- but then I'm not sure I'd like to rely on glue to hold down panels that big and heavy in a gale, if the wind gets under them they could turn into lethal giant frisbees... 😞

 

https://midsummerenergy.co.uk/buy/solar-panel-mounting/solar-mounting-feet-100mm

 

Suggest you look at bimblesolar, cheaper high-output panels, much bigger choice of mounting hardware especially for full-size panels -- they have some strip-type mounts designed for the job which should be fine if glued down since they have at least 10x the glue joint area of the Midsummer Z-mounts...

 

Had a look at bimble solar, and saw these magnetic mounting feet - each one apparently has 20kg of holding power, so there is a total of 80kg holding each panel down, plus its own 20kg mass. If unsure, you could add sikaflex, and maybe a couple of extra magnetic feet...

I like the look of these, I must say, especially given the mess I might make trying to drill and tap holes in the roof for machine screws.

 

https://www.bimblesolar.com/extras/mounting/magnetic-mounts-42

 

 

Edited by Tony1
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2 hours ago, Tony1 said:

 

Had a look at bimble solar, and saw these magnetic mounting feet - each one apparently has 20kg of holding power, so there is a total of 80kg holding each panel down, plus its own 20kg mass. If unsure, you could add sikaflex, and maybe a couple of extra magnetic feet...

I like the look of these, I must say, especially given the mess I might make trying to drill and tap holes in the roof for machine screws.

 

https://www.bimblesolar.com/extras/mounting/magnetic-mounts-42

 

 

Just bear in mind that if you use those magnetic feet a tea-leaf can have your valuable panels away silently in a few seconds equipped with nothing more than a bit of wood to lever the feet off the roof...

 

People have had all sorts of stuff nicked off the outside of boats including generators, gas bottles, diesel, basically anything worth money that isn't nailed down. Expensive solar panels that can very easily be detached might just be too tempting -- and I think these have been nicked too... 😞

 

Of course these occurences are relatively rare but do happen, and making it easy for thieves when you don't have to doesn't seem like a good idea to me.

 

Extra power in the summer can come in very useful as you say -- 6 x 380W panels should average about 7kWh-8kWh per day in summer, which can do a lot including providing hot water.

Edited by IanD
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12 hours ago, Tony1 said:

 

Had a look at bimble solar, and saw these magnetic mounting feet - each one apparently has 20kg of holding power, so there is a total of 80kg holding each panel down, plus its own 20kg mass. If unsure, you could add sikaflex, and maybe a couple of extra magnetic feet...

I like the look of these, I must say, especially given the mess I might make trying to drill and tap holes in the roof for machine screws.

 

https://www.bimblesolar.com/extras/mounting/magnetic-mounts-42

 

 

Buy self drilling bolts then Tony, 8 mm head electric drill with socket in it job done, they even have washers with rubber seals on them, PU adhesive as well no leaks and no rust Screwfix sell them

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I fabricated my mounts from 40 x 40 x 5 Aluminium angle - 30 x 30 sq. bar drilled and fixed to roof with stainless bolts into Riv-nuts - sealed. I use short and long extrusion pieces depending on the time of year to tilt - and which way I'm moored - I won't cruise during winter anyhow, so the panels can stay raised until 15 February.

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12 hours ago, peterboat said:

Buy self drilling bolts then Tony, 8 mm head electric drill with socket in it job done, they even have washers with rubber seals on them, PU adhesive as well no leaks and no rust Screwfix sell them

 

Cheers Peter, I'll get some of these- I'll check, but I think the bimble solar panel mountings have 6mm holes, which seems a tad small. But they must be ok to use- bimble have a decent reputation.

 

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6 hours ago, alistair1537 said:

I fabricated my mounts from 40 x 40 x 5 Aluminium angle - 30 x 30 sq. bar drilled and fixed to roof with stainless bolts into Riv-nuts - sealed. I use short and long extrusion pieces depending on the time of year to tilt - and which way I'm moored - I won't cruise during winter anyhow, so the panels can stay raised until 15 February.

 

Thanks Alastair. I did quite like being in the marina last winter, in that everything was to easily to hand, including water, coal, all sorts of shops, etc- and there was a sense of safety and security. There was even an electrical hookup (which worked out much cheaper than running the engine to create electricity).

But when I finally left at the end of March, I really did enjoy the sense of freedom. 

I'm not going to cruise very far next winter, but I will still be CCing in the general area of Cheshire, Shropshire and Staffs- at least as far as closures will allow. 

 

So I wont be able to rely on getting extra power from tilting my panels up. There will be some suitable moorings to face the panels south and gain the extra power, but probably not lots. 

I think my plan will be to find some locations where there is a small town within 5 miles, where the towpaths are half decent for cycling, and where it's not too overlooked by trees etc. 

I'll probably move between a couple of dozen good mooring spots, but I wont be able to be too picky about the solar benefits of any particular spot. 

 

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  • 4 months later...

Sorry to dig up a slightly old thread and to back-track a bit to the discussion on alternator charging lithium batteries…

 

I’ve got a 170amp dedicated alternator for charging the house battery and a separate, smaller one for the starter battery. Victrons BMS 12/200 seems like a great way of getting a fairly hefty regulated current into the batteries but I think it only works with Victron batts… 

 

The DC to DC chargers whether Victron or otherwise also look good but they are expensive! The largest rated 12v - 12v one is 30amps so you might need 4 of these to get a decent charging current from your alternator and that’d set you back £800. The Sterling one is better value at about £450 for the 120a model. 
 

A lot of the information is based around vehicles with just one alternator, does anyone have advice on an effective set up using 2 alternators? Is the larger alternator connected just to the house battery or to the starter as well, how is it protected in the event of the BMS stopping charging when batts are full/cold etc? 
 

The Renogy one looks quite good, mush better price. I wonder if 2 of these could be paralleled to get a higher output… 

 

https://uk.renogy.com/12v-60a-dc-to-dc-on-board-battery-charger/

 

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10 minutes ago, WillCful said:

Sorry to dig up a slightly old thread and to back-track a bit to the discussion on alternator charging lithium batteries…

 

I’ve got a 170amp dedicated alternator for charging the house battery and a separate, smaller one for the starter battery. Victrons BMS 12/200 seems like a great way of getting a fairly hefty regulated current into the batteries but I think it only works with Victron batts… 

 

The DC to DC chargers whether Victron or otherwise also look good but they are expensive! The largest rated 12v - 12v one is 30amps so you might need 4 of these to get a decent charging current from your alternator and that’d set you back £800. The Sterling one is better value at about £450 for the 120a model. 
 

A lot of the information is based around vehicles with just one alternator, does anyone have advice on an effective set up using 2 alternators? Is the larger alternator connected just to the house battery or to the starter as well, how is it protected in the event of the BMS stopping charging when batts are full/cold etc? 
 

The Renogy one looks quite good, mush better price. I wonder if 2 of these could be paralleled to get a higher output… 

 

https://uk.renogy.com/12v-60a-dc-to-dc-on-board-battery-charger/

 

 

I have roughly the sort of setup you describe, and I can give you some pros and cons, but I have to say up front that B2Bs are NOT the way I would go if I were starting all over again.

 

An alternator controller such as the mastervolt unit can do all of what my complex B2B setup does, but a lot more efficiently and simply.

You can probably have that unit supplied and installed by Ed Shiers of Four Counties Marine (who is a genuine expert in this field) for around £600-£700- job done.

 

If you have a good quality 170 amp alternator, I would guess you can probably have it putting out at least 120 amps continuous charge without getting too hot, which means all of your daily electricity usage can be put back into the batteries in less than an hour of engine running. 

 

I would also add that if you have lithium batteries, solar panels would be a great investment as they work really well with lithiums, so that about 1000 watts of panels will mean you wont need to run the engine at all (for recharging anyway), for maybe 8 months of year. 

 

If you go down the B2B route, there are a number of things I've observed that you might bear in mind: 

 

Sterling sell a B2B unit rated at 60 amps input, for about £300 (the BB1260).

I have two of these, and they put out around 45-50 amps, but more annoyingly, they seem to sometimes throttle back to 40 amps or less, as I think the internal heat control systems kick in and reduce their output. Its a shame as they are incredibly flexible units with all sort of configurability and options, but one thing that is not configurable is the output current. You have the option of full power (about 50 amps), or half power (about 30 amps). 

 

You could parallel two of these to get about 100 amps, but I think they lose a lot of energy in operation, give off a lot of heat, and I don't know whether they will give the full 50 amps each continuously, or will throttle back periodically as mine seem to do. I'm not writing them off, because I'm no expert- but I would look into that very carefully before parting with £600 for two of these units. On the plus side, Sterling's technical support is very good- I just didnt have the electrical nous to fully grasp the details that were explained. 

 

They are a very safe option for lithiums, in the sense that they absolutely will not give out more than 50 amps (maybe 55 amps), so your alternator will never be overworked and thus overheat, but an alternator controller is a simpler option, and probably cheaper overall.   

I understand that the mastervolt unit is even smart enough that it reduces the draw from the alternator at lower revs, and increases it as the revs increase, so you avoid drawing huge current from the alternator at tickover.  

 

My system uses two lead acid batteries (one of which is the starter battery). Each of these lead acid batteries is fed by its own alternator, and each acts as a source, being wired to a B2B unit, and from the B2Bs the current feeds into the batteries via a fuse, etc. 

I only set it up this way because I dont have a single high-power alternator such as you have. My alternators are rated at 100 and 90 amps respectively, but I find that if they put out more than 50 and 40 amps they quickly get to 100 degrees and beyond (normal operating temp is around 60 degrees, so 100 degrees plus is a concern in the longer term). 

 

Out of interest, I did notice that they can give more output and stay fairly cool at higher revs, since the fans are running faster, but on a day to day basis you need a system that runs safely at high or low revs. 

 

But you dont need a complex mish mash as I've got. Even if you do go down the B2B route , your 170 amp alternator should run two B2Bs on its own, and thus leave the other alternator to charge the starter battery. 

 

I looked at the Renogy units, but I have no info about how they perform. That said, there will be user off-grid and yachting forums that discuss these, so there will be info out there. 

I would have loved a victron B2B, but as you'll have seen they only do a 30 amp unit, so you'd need 4 of these to get 120 amps charging current, and that gets you over £800- and for that money you could have an alternator controller professionally fitted. 

 

 

 

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43 minutes ago, WillCful said:

Sorry to dig up a slightly old thread and to back-track a bit to the discussion on alternator charging lithium batteries…

 

I’ve got a 170amp dedicated alternator for charging the house battery and a separate, smaller one for the starter battery. Victrons BMS 12/200 seems like a great way of getting a fairly hefty regulated current into the batteries but I think it only works with Victron batts… 

 

The DC to DC chargers whether Victron or otherwise also look good but they are expensive! The largest rated 12v - 12v one is 30amps so you might need 4 of these to get a decent charging current from your alternator and that’d set you back £800. The Sterling one is better value at about £450 for the 120a model. 
 

A lot of the information is based around vehicles with just one alternator, does anyone have advice on an effective set up using 2 alternators? Is the larger alternator connected just to the house battery or to the starter as well, how is it protected in the event of the BMS stopping charging when batts are full/cold etc? 
 

The Renogy one looks quite good, mush better price. I wonder if 2 of these could be paralleled to get a higher output… 

 

https://uk.renogy.com/12v-60a-dc-to-dc-on-board-battery-charger/

 

 

It might be worth starting a new thread on this subject.

My boat had the lithium's installed by the previous owners. It has a 160ah lithium as the house battery and a 100ah starter battery, and the engine has a 40a starter and 100amp house alternator. It looks to have been professionally installed, but the installer clearly couldn't work out how to utilise the twin alternator setup, so only the 40a alternator is utilised to charge both the lead acid and lithium.

 

I have tried to look into using the 100a alternator to charge the lithium, but it's not straightforward....connecting it direct to the lithium will destroy the alternator. I think there are smart regulated alternators you can get now that can charge lithium batteries directly, but I'm not sure! 

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