Overstressed alternator?

[zoidberg]

I have a Beta 14 c/w a 200-07338 Mini 75A compact alternator. I've just had fitted an 314Ah LFP battery and an Optima AGM LA unit for Start, with a DC/DC charger.
I've become a little concerned that, should I end up motoring for hours, the LFP battery will absorb everything the alternator can produce.... and it, the alternator, may then become severely overheated and fail.

Am I fretting about nothing?

If not, how best may I address the problem?

 

[Tranona]

The DC/DC will limit the amount of charge to 30A? so no danger of overloading the alternator. That is the whole point of using that method.

 

[Poecheng]

....and you program the DCDC charger so that its output is set for lithium.
Once the lithium is charged, the continual (absorption) charge should be avoided by the DCDC output charge dropping down to 13 something so that it is not continually adding low current into the LFP

 

[Buck Turgidson]

I did a little sanity check when I fitted my Lthium. I've got a 50 year old Yanmar with a 35A alternator so I ran the cool box and some other stuff all night open to take the batter down to 50% then next day with my dc/dc set to 15A max went motoring with a temperature sticker stuck to the Alt. it never got above 45°c and the battery was 100% in about 3 hours.

 

[zoidberg]

So I'm probably fretting about nothing....

I'll go get a temp sensor/sticker from somewhere. That'll give me something else to watch.

 

[Trident]

You are fretting over nothing - the DCDC is set up to 50% of the alternator capacity for that very reason - it can not allow the LFP to take too much and stress the alternator . The alternator can run all day at 50% capacity

 

[zoidberg]

You are fretting over nothing

It's in my nature!

Now I'll need to go find something else....



( And I've fitted the little jumper thingy.... on a string so it can't now go walkabout very far. )

 

[Neeves]

Have you fretted, in public, over your choice of anchors. If not - now might be the time.

Jonathan

 

[Dockhead]

So I'm probably fretting about nothing....

I'll go get a temp sensor/sticker from somewhere. That'll give me something else to watch.

I don't think you are, actually.

As others have said, you're set up well if the DC-DC is limiting the draw of the lithium to 30A. That should be fine, but it's sensible to monitor temperature. I do on my boat; I even have an alarm.

A lot of alternators have died at the hands of lithium batteries.

 

[noelex]

A continuous output of 50% of the rated output is considered safe for ”standard” marine alternators. Some models will protect themselves better, but the risk of alternator burn-out becomes a concern if this number is exceeded on many standard models.

Providing you have fitted one of the common DC to DC chargers limited to 30A, you are under this threshold so should be fine without any intervention. If the DC to DC charger is larger than 30A, there may be a problem.

If you have fitted a larger DC to DC charger, the output can sometimes be dialled back via the software. 50% is a good starting point, but you can measure the alternator temperature and adjust this up or down.

The lead acid start battery charges so quickly that the output will not normally overheat the alternator, so its energy absorption can largely be ignored.

An external regulator with temperature monitoring would extract more energy while more accurately keeping the alternator temperature within safe boundaries, but the improvement is only worthwhile if you swap for an alternator model designed for high-output continuous charging.

 

[zoidberg]

A continuous output of 50% of the rated output is considered safe for ”standard” marine alternators. Some models will protect themselves better, but the risk of alternator burn-out becomes a concern if this number is exceeded on many standard models.

Providing you have fitted one of the common DC to DC chargers limited to 30A, you are under this threshold so should be fine without any intervention. If the DC to DC charger is larger than 30A, there may be a problem.

If you have fitted a larger DC to DC charger, the output can sometimes be dialled back via the software. 50% is a good starting point, but you can measure the alternator temperature and adjust this up or down.

The lead acid start battery charges so quickly that the output will not normally overheat the alternator, so its energy absorption can largely be ignored.

An external regulator with temperature monitoring would extract more energy while more accurately keeping the alternator temperature within safe boundaries, but the improvement is only worthwhile if you swap for an alternator model designed for high-output continuous charging.

Thanks, noelex, for the above.
I'll implement that.

Meanwhile, I'm up to my scuppers in multi-crimping.....