DC to DC charger - not needed for boats with proper alternators.

[CaptainRivet]

Originally Posted by newhaul

Let's see 70 amps out of a 105 amp alternator is approx 68% of total possible . So you are derating the alternator by just over 30% which reduces the heat considerably. And at 3800rpm there is plenty of cooling air to keep the alternator from overheating.
Aside from how long do you actually think the 70amp output would really be needed.

The delco remy 36 is a schoolbus alternator type designed for high loads on low revs, so it would be fine with this, no problem.

[hjohnson]

Originally Posted by newhaul

One question why no solar on a sailboat? My 200 watts charges me right up .

27’ boat. I’ve got 120W on the dodger, and another 200w foldable that I can put out when I’m be at anchor or at the dock. The 120W can keep up with my systems in the summer.

But I tend to do much of my sailing in the winter, when not only do we get down to 9 hours of daylight, but much of the time It’s raining or at least heavily overcast. That said, when it drops below freezing, and is sunny, the panels become more efficient.

But in reality, it’s mostly that I just can’t for enough panels to be useful as anything more than a range extender.

[Simi 60]

Originally Posted by newhaul

Let's see 70 amps out of a 105 amp alternator is approx 68% of total possible . So you are derating the alternator by just over 30% which reduces the heat considerably. And at 3800rpm there is plenty of cooling air to keep the alternator from overheating.

We smoked 2 previous large frame alts (less amps but same size case) trying to charge AGM via a VSR.
Worked for a bit until it didn't.

[newhaul]

Originally Posted by hjohnson

27’ boat. I’ve got 120W on the dodger, and another 200w foldable that I can put out when I’m be at anchor or at the dock. The 120W can keep up with my systems in the summer.

But I tend to do much of my sailing in the winter, when not only do we get down to 9 hours of daylight, but much of the time It’s raining or at least heavily overcast. That said, when it drops below freezing, and is sunny, the panels become more efficient.

But in reality, it’s mostly that I just can’t for enough panels to be useful as anything more than a range extender.

Funny I prefer winter as well that's the only time we get reliable winds . Not to mention how beautiful the San Juan Islands are when nobody is there.

[newhaul]

Originally Posted by Simi 60

We smoked 2 previous large frame alts (less amps but same size case) trying to charge AGM via a VSR.
Worked for a bit until it didn't.

But not derated by a third .
That 70 amp draw out of 105 amp alternator is the key to your alternator surviving long term.

[motion30]

Originally Posted by Simi 60

But if I have a smart regulator why would I need DC- DC chargers?

I thought the whole idea of smart regs like the Balmar or Wakespeed was so I could charge from alt direct to Lifepo4 bank?

But that's not the whole story. Does your smart regulator allow you to charge the Start batteries and the house battery bank without them being connected?

[Simi 60]

Originally Posted by newhaul

But not derated by a third .
That 70 amp draw out of 105 amp alternator is the key to your alternator surviving long term.

They would have been derated by a 3rd if the charge curve was the same and the rpm were the same.

[newhaul]

Originally Posted by Simi 60

They would have been derated by a 3rd if the charge curve was the same and the rpm were the same.

No the derate using the dc 2dc is different derated but still turning at top efficiency for cooling is a different critter.

[sailingharry]

A significant problem with using a dc/dc charger to protect the alternator is it only derates the alternator at cruising speed. If you are running the engine at 1000 RPM for a while, not an ideal situation but possible, you could well see an overheated alternator (the DC to DC converter will be pulling more than the alternator can make). A smart external regulator protects the alternator in all operating conditions. It also gives you full output early in the charge cycle, which is helpful if you are only going to run the engine for 10 or 20 minutes.

[hjohnson]

Originally Posted by newhaul

Funny I prefer winter as well that's the only time we get reliable winds . Not to mention how beautiful the San Juan Islands are when nobody is there.

One of these years we’ll get up to Princess Louisa Inlet for New Years. Foiled twice now; two years ago by the heavy freezeup making potable water impossible to find, and last year heavy winds in the southern strait making it unsafe to bring the big boat up from Anacortes. Next year, maybe, we’ll make it.

[hjohnson]

Originally Posted by motion30

But that's not the whole story. Does your smart regulator allow you to charge the Start batteries and the house battery bank without them being connected?

Nah, there, a cheap dc-dc charger will maintain your start battery without any fuss. Also useful if you have a dual voltage system (12V starter, 24V house bank).

[newhaul]

Originally Posted by hjohnson

One of these years we’ll get up to Princess Louisa Inlet for New Years. Foiled twice now; two years ago by the heavy freezeup making potable water impossible to find, and last year heavy winds in the southern strait making it unsafe to bring the big boat up from Anacortes. Next year, maybe, we’ll make it.

Cap Santee? We home out of there for the summer crab season with the big boat .
The FV Sikai.

[Nicholson58]

Originally Posted by Simi 60

I still don't get this DC to DC charger saving the alt.

I am looking at fitting a 36si Delco Remy 105 amp @ 24v to our engine
At our 1150 cruise RPM there is 3800rpm at the pulley so we should be seeing 80amps.

Sterling 24v 35 amp DC to DC chargers X 2 is 70 amps pulling from the starts and alt.
Surely that'll still smoke the alternator if running for hour after hour after hour

The short version is that most alternators cannot output their full maximum rated output indefinitely. I have burned out several motor sailing all day or night. A large lithium bank or even a large AGM appears to the alternator as a giant short. We use a Balmar external charge controller limiting our alternator output to 50%. 80% was not enough with the alternator in a hot engine room in the tropics. You can also use a DC-DC converter as long as the end result is limiting the alternator output. I like the external controller and I believe one should have this anyway. One additional consideration is a cut off switch to turn off the alternator at near full charge. On an external regulator this switch is in line with the power from the oil pressure switch. The Balmar manual is clear what wire turns it on.

[Simi 60]

Originally Posted by hjohnson

Nah, there, a cheap dc-dc charger will maintain your start battery without any fuss. Also useful if you have a dual voltage system (12V starter, 24V house bank).

Find it hard to believe after spending the $$ that we'd have to go backwards and buy yet another charger.

Got to be a way of doing starts first and then house which is why I mentioned an AVR like the victron cyrix earlier.

If we had to have a backwards charger I do have a 240v victron ip67 24v 12amp charger which I used for the year we had no alternator at all
But seems a backwards step

[hjohnson]

Originally Posted by Simi 60

Find it hard to believe after spending the $$ that we'd have to go backwards and buy yet another charger.

Got to be a way of doing starts first and then house which is why I mentioned an AVR like the victron cyrix earlier.

If we had to have a backwards charger I do have a 240v victron ip67 24v 12amp charger which I used for the year we had no alternator at all
But seems a backwards step

The issue is that Lithium and Lead need significantly different charging profiles. On my boat, the alternator is doing strictly what the Lithium BMS is calling for, and that would not be healthy for the Lead.

The prime example is that most of the time, I want my Lithiums sitting at between 13.2v and 13.3v where it's best to let them rest, but I want the Lead to be sitting at 13.8v, which is where you want to store Lead.

The Orion-Tr I have was like $200, which isn't significantly more expensive than other options, and does its job with aplomb.