Visit our Popular Forums

RaymondR · 10-10-2021, 13:43

"It think the idea that lithium batteries will kill your alternators by making them output huge amounts of power (supposedly due to their low resistance), is simply wrong. Alternators regulate to a voltage, they don't care about the resistance. An alternator (on any any battery that can accept its full charge, include big LA bank) with a regulator that doesn't sense the temp of the alternator, seems to be the issue here?"

One of the ways to prevent an alternator from overheating and burning out is to introduce more resistance into the charging circuit to fool the regulator into "seeing" a higher battery voltage and consequently reducing the current output.

JustMurph · 10-10-2021, 14:02

I totally agree and that's exactly why (for example) the big alternator on my mates boat doesn't work all that hard, unless a big load gets turned on and drags the voltage down. We really need to upgrade the wiring, or use an external regulator.

Flod · 10-10-2021, 14:05

Quote:

Originally Posted by JustMurph

We've recently changed from lead acid to LiFePO4 in a mates cat and have found no change in the outputs of the alternators (3GM30s, one with a standard Hitachi 55A and one with a larger alternator of unknown spec). In fact both produce slightly less power, as the voltage the alternator sees is higher.

Likewise in the old setup in my cat, there was no issue charging a LiFePO4 bank with my 3YMs, from their pair of standard Hitachi 55s. Just as with the lead acid, they charge at a high rate for a while, then output drops as they get hot.

So what's the issue here? Standard relatively modern internally regulated alternators seem to have temperature limiting. Do the big aftermarket externally regulated alternators not? How does a big $ master volt not have temperature limiting?

It think the idea that lithium batteries will kill your alternators by making them output huge amounts of power (supposedly due to their low resistance), is simply wrong. Alternators regulate to a voltage, they don't care about the resistance. An alternator (on any any battery that can accept its full charge, include big LA bank) with a regulator that doesn't sense the temp of the alternator, seems to be the issue here?

What am I missing?

I totally agree with this. My standard yanmar Hitachi 60 amp have coped with the transition to lifepo4 without any problems for 3 full seasons now. It outputs 55ish amps for like 45-50 minutes and then get hot and dial down to 12-20A. No problems whatsoever

Hermia II · 11-10-2021, 08:54

I'm with GOBOATINGNOW! This is my exact experience. One can add that many marine "House Bank Alternators" have external regulator. Balmar has two temp sensors, one for the alternator casing, and it can reduce charge by 50% at a certain temp. Mastervolt AlphaPro 2 and 3 has one temp sensor which can be used for either battery or casing. I don't however know how to set it, using the sensor for the casing. Must be different from using it for the battery.

Gert- · 12-11-2021, 01:57

Most alternators are not designed for the typical charge application as used in sailboats. The shift to LiFePo4 increased the problems: long term charging at high amps due to low internal resistance…
Some external regulators are designed to overcome these problems; once set correctly, they can limit the field current of your alternator, based on temperature of your alternator and your battery bank.
I just exchanged my Hitachi alt on my 3YM30 for a standard industrial 90A alternator (Prestolite, just 140€), bypassed it’s standard regulator, added the MV Alpha Pro III controller and a MV shunt. This setup allows me to control the output at low revs (20% capacity of 90A), output at high revs (now set at 50%), and have the temperature sensor of the Alpha Pro limiting the output once the temperature of the alternator gets too high.
I am not a Mastervolt fan at all, but this combination is simply brilliant! The master adjust software allows you to set all thresholds on a laptop, for either FLA or LiFePo4.

skenn_ie · 12-11-2021, 03:13

Quote:

Originally Posted by SV-NoBadDay

Hi,

I am new to lithium batteries and after watching a Victron video on charging lithium a low RPMs i got a little concerned about my current set up.

I have a 14v125A alternator - the max charge current my lithiums will take is 90amps but...I have two...does this make the max amps 180?

I do also have a battery isolators with two AGM banks (as well as the lithium bank) attached to it.

I am wonder if i need to install an external regulator to protect my alternator...anyone know?

Sorry if a silly question...any help would be appreciated.

Thank you
Paul

Install a ballast resistor between the alternator output and the rest of the electrics. Alternatively, an external regulator (recommended on any boat) that has current limiting.

rgleason · 13-11-2021, 01:56

This statment is inaccurate:

larger alternator of unknown spec). In fact both produce slightly less power, as the voltage the alternator sees is higher.

RaymondR · 13-11-2021, 08:49

Quote:

Originally Posted by rgleason

This statment is inaccurate:

larger alternator of unknown spec). In fact both produce slightly less power, as the voltage the alternator sees is higher.

Depends on the size of the ballast resister and whether one has a battery voltage sensing circuit between regulator and battery terminal.

I have used a bike spoke in the charging connection between alternator and battery terminal and just slid the connecting wires together and apart on the spoke to adjust the alternator output as a contingency measure.

skenn_ie · 13-11-2021, 09:32

Quote:

Originally Posted by Stu Jackson

Yes, you should get an external regulator.

Have you already installed the Liths?

The reason is simple: only an external regulator, preferably with temp sensors, will allow you to dial back the AO so it doesn't burn up due to the high acceptance of Liths.

It's also true for AGMs.

You should also get rid of the isolators, which drop Voltage thru them by ).7 to 1V.

WADR, it appears you could use some reading on this subject. Try marinehow.com Is for Sale.

Trivia: I is the symbol for current so Io is output current. Amps is the unit of measure.

Non-trivia: There is a circuit referred to as an "ideal diode" which does the job of a rectifier but with a voltage drop usually of 30mV. Check eBay for supplies.
Infineon in collusion with Bosch, produce a press-fit rectifier with a forward voltage of 0.1V, but so far, I haven't been able to find if they can be bought. AFAIK, they are only available to manufacturers of alternators.

skenn_ie · 13-11-2021, 09:37

Quote:

Originally Posted by Stu Jackson

WADR, huh?!?

The internal regulator measures the V at the back of the alternator, and is preset, usually not adjustable. So, let's say it is set for 14.2V.

The AO goes out and to an isolator that drops let's say 0.7V. 14.2 minus 0.7 = 13.5V.

That's the highest V that can get to the batteries (neglecting voltage drop completely ford this discussion).

All that will happen is that the batteries will be woefully undercharged, and NOT "causing the regulator to wind back the alternator output." That will simply not happen, it is not how it works.

You can compensate for the isolarot voltage drop by inserting a diode between the sense input of the regulator and the alternator output. That will boost the alternator output by approx 0.7V.

skenn_ie · 13-11-2021, 09:43

Alternators with integrated regulators usually have air circulation from forward speed of a road vehicle. Even with the fan which usually accompanies them, they probably don't get the cooling that they require for longevity. That is just part of the recommendation to mount the regulator remotely. Digital "intelligent" regulators are better still as they do a significant amount of on-the-fly analysis of battery and alternator.

goboatingnow · 13-11-2021, 09:48

The issue isn’t specific to lithium per se. If you up the charging voltage from the alternator with lead acid , the same overheating occurs. Secondly boat alternators are often running at low speeds and hence cooling is inadequate not helped by the engine enclosure.

Lithium just exposes the same issue at the stock alternator voltage. You can run the output through a big diode and reduce the alternator output accordingly ( sensing on the alternator side of the diode )

rgleason · 13-11-2021, 09:55

Yes. Agreed. They are fooled and putting out less. Its not an ideal situation however.

LeighC · 13-11-2021, 16:19

I thought when you lower the voltage at the sense wire of the alternator the voltage goes up at up at the battery which is exactly what you don't want with LIFeP04, I am trying to raise the voltage at the sense wire, what is the best way to do that?
Thanks - Leigh