Am I risking my 20-year-old 60a alternator by installing a 30a 12v DC DC charger?

[Duggy]

Long-time lurker, first time poster.... (in fact, I have just realised I am coming on for 20 years using this forum and this is my first post!).

So - I am one year into owning my 2004 Beneteau Oceanis 331, which I am thoroughly pleased with. I keep the boat on a mid-river pontoon without shore power and I find myself in a constant state of worry that I will drain the two 100ah lead-acid batteries it came with if I spend any amount of time on the boat without running the engine (which I prefer to do only under load when I am actually out). I have no solar currently and no other means for generating power.

As a result, I have been buying various power upgrades over the last few months that I plan to install now I am on the hard over winter, including a 300ah Fogstar LiFePO4 battery, a Victron EasyPlus inverter/charger, various eye wateringly expensive tinned cables, busbars, solar panel, MPPT controller etc...

As per the thread title, I was just on the verge of puchasing a Victron 30a DC DC charger (so I could safely get some charge into the new house LiFePO4 battery from the engine when out and about), which I had sized based on it being 50% of the rated 60a output of the factory alternator that comes with the VP MD2030. However, it has occured to me that my 20 year old alternator is probably not as effective as it once was and since even new alternators are unlikely to generate more than 90% of their max rated amps at high revs, I am guessing that my alternator will have diminished somewhat over time and may be generating much less than 60a these days. How critical is this likely to be? Is this even an issue I need to be concerned about?

Obviously, I do not want to burn out the alternator if there is still some life left in it, but I am hesitant to downgrade to the Victron 18a DC DC charger and reduce my potential LiFePO4 charge rate, particularly if I find myself needed to replace the alteranator anyway at some point in the future.

Any advice/suggestions would be welcomed.

 

[PaulRainbow]

Welcome to the forum.

Your alternator will be fine.

 

[noelex]

You should not be concerned.

If you have any doubts, checking the alternator temperature with an infrared gun (a valuable tool on a boat) under several typical conditions will provide confirmation. The highest alternator temperature is usually observed at relatively low or moderate revolutions, where the alternator cooling is reduced (rather than when the engine is flat out).

Although I do not possess a Victron 30A DC to DC charger, I believe that the charging rate can be reduced via software, but it is unlikely you will need to do this.

 

[Refueler]

a) As Paul says - alternator should be fine.

but

b) I would seriously look at finding a way to keep all your batterys charged while boat is idle at mooring ... solar / wind or whatever .... NOT keeping the batterys up will be the killer that you are afraid of ..

 

[lustyd]

Although I do not possess a Victron 30A DC to DC charger, I believe that the charging rate can be reduced via software

Only on the new Orion XS, the older one didn't have this. A 30A will be fine, I had one on my similar setup and then replaced it with the XS which I downrated to 30A. I upgraded because the new one runs cooler and is slightly more efficient.

 

[Duggy]

Thanks for the quick responses from everyone. Reassuring to hear that this should be OK.

@Refueler - yes, I agree that I will need some sort of additional power source to ensure that I am keeping topped up. The last owner kept the boat in similar circumstances on a mid river pontoon and I suspect that the LA batteries often did not receive any charge for long periods of time. I am planning a fixed solar panel somewhere on the boat (exact location TBD) and perhaps also scope to have a roving panel I can bring out and position to supplement charge when I'm aboard.

@lustyd - useful to hear your experience with the 30A Orion. I can live with it being fixed at 30A as long as the alternator doesn't mind

 

[ithet]

Duggy,
Glad to see you have ventured onto the forums!

Can't advise on the alternator as I have a VCR and 3*95ah LA house batteries on my 331, max I have seen it put out is 45A. But I have a Photonics Universe 80AH semiflex panel which fits neatly on the hatch garage and keeps batteries well topped up via a Victron smart MPPT. I intend to get a large portable panel for when several days at anchor.

 

[Duggy]

I figured it was long overdue

I am definitely leaning towards using the hatch garage for mounting my solar as well. I realise that this location is not optimal because of boom shade, but it is space that is otherwise going unused and any benefit I can get for the cost of a panel feels worth it. It is good to hear that your 80w panel is enough to keep your batteries topped up while you are away.

 

[ithet]

I figured it was long overdue

I am definitely leaning towards using the hatch garage for mounting my solar as well. I realise that this location is not optimal because of boom shade, but it is space that is otherwise going unused and any benefit I can get for the cost of a panel feels worth it. It is good to hear that your 80w panel is enough to keep your batteries topped up while you are away.

Realised it is the 60W I have, but this works OK even brings batts up a bit. Boom shading is an issue but these ones have two parallel circuits of cells which helps. The 80W would just fit (I think) but come right to edge of the garage and could get trodden on. A bigger panel could be fitted by rebuilding the air vent but I think a portable panel strategically positioned when at (occasional anchor) is my way forward. BTW, we managed five consecutive nights off grid this summer with just two days having to top up with engine.

 

[lustyd]

two parallel circuits of cells

Two strings, connected in series with bypass diodes. It won't help as your panel voltage is 9V when one side is in bypass, which is too low to charge your battery. You'd need another panel in series to make this effective since then it could hit 27V with one string shaded or 18V with two shaded in any combination.

I suspect in reality your panel is shaded a lot less that you imagine. Ours are across the coachroof so in theory all 4 strings on the two panels are shaded by the boom but almost never are.

 

[Alex_Blackwood]

Two strings, connected in series with bypass diodes. It won't help as your panel voltage is 9V when one side is in bypass, which is too low to charge your battery. You'd need another panel in series to make this effective since then it could hit 27V with one string shaded or 18V with two shaded in any combination.

I suspect in reality your panel is shaded a lot less that you imagine. Ours are across the coachroof so in theory all 4 strings on the two panels are shaded by the boom but almost never are.

?? from his photo, he has 18 cells in the panel I suspect, only suspect as I have no real knowledge of the panel, that there are two sets of 9 series connected cells connected in parallel. Could be wrong, not unknown.

 

[rogerthebodger]

I have a solar panel on my hatch garage andto prevent shading I simplly position my boom on the sout side of the boat *I am in the soutern hephere) if in the noth poition the boom on the north sied to maxanize the sun on the solar panel

 

[lustyd]

?? from his photo, he has 18 cells in the panel I suspect, only suspect as I have no real knowledge of the panel, that there are two sets of 9 series connected cells connected in parallel. Could be wrong, not unknown.

It's a pretty standard setup these days and common to all panels with two bypass diodes. There are two strings of cells, each with a bypass diode. All cells are in series, but each half can be bypassed if shaded.

It's too complex/expensive to add a bypass for each cell, but that would in theory be better.

 

[PaulRainbow]

?? from his photo, he has 18 cells in the panel I suspect, only suspect as I have no real knowledge of the panel, that there are two sets of 9 series connected cells connected in parallel. Could be wrong, not unknown.

It's a pretty standard setup these days and common to all panels with two bypass diodes. There are two strings of cells, each with a bypass diode. All cells are in series, but each half can be bypassed if shaded.

It's too complex/expensive to add a bypass for each cell, but that would in theory be better.

Sorry gents, but you are both mistaken.

That particular panel is made up of 36 half cells. 18 half cells in each string, the two strings then connected in parallel.

Each half cell is 0.5V ( or thereabouts), so each string is 18V (or thereabouts). The 2 strings in parallel are then obviously 18V. If part of one string is in shadow you still get 18V from the other string, but a reduction in voltage and current from the string in shadow.

Shading has a greater effect than might be expected, even with this type of panel. You only need to cover a small area of panel and the voltage loss can render that string virtually useless.

 

[lustyd]

Thanks Paul, couldn’t see any mention of that on the product page so assumed it was standard other than the 5 busbar cells. The PU website seems remarkably lacking in detail.
60W semi flex panel

 

[Alex_Blackwood]

Sorry gents, but you are both mistaken.

That particular panel is made up of 36 half cells. 18 half cells in each string, the two strings then connected in parallel.

Each half cell is 0.5V ( or thereabouts), so each string is 18V (or thereabouts). The 2 strings in parallel are then obviously 18V. If part of one string is in shadow you still get 18V from the other string, but a reduction in voltage and current from the string in shadow.

Shading has a greater effect than might be expected, even with this type of panel. You only need to cover a small area of panel and the voltage loss can render that string virtually useless.

What's half a cell between friends.
Becomes clear when looking at the PU website picture rather than the photo.