Alternator burn out charging lithium

[lmxr]

Originally Posted by LeighC

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

Nordkyn VRC-200


Not the cheapest but it does convert your alternator to a smart charger.

[team karst]

Originally Posted by goboatingnow

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 )

Diesel engine enclosures should take the forced outbound air from up high, and the replenish air injects down low. This is how cooling should take place. Now, it becomes a race of alternator death from overheating vs salt air induced corrosion. [emoji51]

This is exact opposite from gasoline systems trying to remove fumes.

[goboatingnow]

Originally Posted by LeighC

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

No. The sense voltage is merely the actual voltage present at the battery minus any voltage drop in the cables.

If you add a diode in series but sense on the alternator side of the diode then lower voltage at the battery will limit the current

[LeighC]

The 4wd off road guys in the Toyotas buy a special fuse that slots in the blade receptacle of the sense wire incorporating a diode in series & it tells the alternator that the voltage in the battery is 0.6 volts lower than it really is & this raises the battery voltage at the B+ terminal & hence the battery to around 14.7volts to fully charge a deep cycle wet calcium LA battery for camping, the current doesn't start to back off till it nears the 14.7volts, this is what I have found, I want to do the opposite for LIFep04, may be I can use a simple op-amp.

[LeighC]

Thanks for the reference to the Nordkyn VRC-200, yes I have read about them before,
they are the ultimate that I need if I had money, just trying to work out a cheaper solution. Thanks - Leigh

[goboatingnow]

Originally Posted by LeighC

The 4wd off road guys in the Toyotas buy a special fuse that slots in the blade receptacle of the sense wire incorporating a diode in series & it tells the alternator that the voltage in the battery is 0.6 volts lower than it really is & this raises the battery voltage at the B+ terminal & hence the battery to around 14.7volts to fully charge a deep cycle wet calcium LA battery for camping, the current doesn't start to back off till it nears the 14.7volts, this is what I have found, I want to do the opposite for LIFep04, may be I can use a simple op-amp.

Yes that’s the effect of a diode in the sense line. I didn’t suggest that. I suggested a diode in the charge line sensed on the alternator side of the diode. This just lowers the charge voltage

[lmxr]

Originally Posted by LeighC

[...]I want to do the opposite for LIFep04, may be I can use a simple op-amp.

An op-amp, a few resistors and a 5$ step-up converter from ebay to generate the higher voltage might do the trick of lowering the voltage. Another approach might be a resistor in the sense line powered by a little isolated DC-DC converter that pushes a small current through the resistor in the direction of the battery.

I guess it will sort of work but I do not expect it to perform anywhere close to a system that actually measures the alternator current and temperature and regulates based on that.

[LeighC]

Thanks Goboating now, sorry I misunderstood that you were talking about the B+ line out of the alternator, what diode would I need to handle 80amps & would I need a heat sink & would I be wasting power? Thanks - Leigh

[RaymondR]

Originally Posted by goboatingnow

No. The sense voltage is merely the actual voltage present at the battery minus any voltage drop in the cables.

If you add a diode in series but sense on the alternator side of the diode then lower voltage at the battery will limit the current

The sense circuit is designed so that the voltage input to the regulator is not by a current carrying conductor and there for there is no voltage drop between battery terminal and sense input to the regulator. E=IR, no I and therefor no E.

Putting a diode in the sense circuit will lower the voltage sensed by the regulator and it will therefor increase the excitation current to the alternator which will increase the current output which, if you are trying to reduce alternator heating, will have the opposite effect to that desired. Putting say a 1.5 volt battery in series with the main battery in the sense circuit would reduce the output.

The simplest way to reduce the alternator output is to put a resistance in the output downstream of the battery voltage sensing point which, in the case of a regulator with external sensing requires moving the sense circuit from the battery terminal to upstream of the resistance.

[LeighC]

Thanks RaymondR, Good idea, I will try a 1.5v dry cell in series with the sense wire to start with and see how it works when I get a chance, I was going to try a separate power supply, but the battery will be safer to prove a point. My belt set up is below par for high current & I have seen 110°C alternator body temps also.
Thanks everyone for their help, I will post the outcome - Leigh

[team karst]

Hopefully, the sense wire doesnt also source the field winding, which would significantly increase the current required. Do U have the capability to measure dc currents of several amps? D+ is a source of limited power, DF terminal might be a field input node.
My internal regulated alternator has a separate yellow wire that both powers the field, plus senses the remote Voltage. I can disconnect that yel wire, and the alt shuts down. When connected, it senses the house batt voltage, trying to keep it at 14.3 volts.

[goboatingnow]

I fail to see how raising the sense voltage will result in lower current to the battery. If the battery voltage plus the cell voltage is still below the alternator internal reference voltage , it will still pump out max field current.

[SailRN]

How not to blow out your alternator charging lithium batteries:

https://www.youtube.com/watch?v=jgoIocPgOug

And the lithium battery's BMS will disconnect, and if the alternator is charging at the time a load dump and spike will occur, creating diode and electronic mayhem on boat's electronics

[goboatingnow]

Originally Posted by RaymondR

The sense circuit is designed so that the voltage input to the regulator is not by a current carrying conductor and there for there is no voltage drop between battery terminal and sense input to the regulator. E=IR, no I and therefor no E.



Putting a diode in the sense circuit will lower the voltage sensed by the regulator and it will therefor increase the excitation current to the alternator which will increase the current output which, if you are trying to reduce alternator heating, will have the opposite effect to that desired. Putting say a 1.5 volt battery in series with the main battery in the sense circuit would reduce the output.



The simplest way to reduce the alternator output is to put a resistance in the output downstream of the battery voltage sensing point which, in the case of a regulator with external sensing requires moving the sense circuit from the battery terminal to upstream of the resistance.

I’m sorry there could be literally micro amps flowing in the sense circuit , and most sense lines are current sinks , A resistance in the sense line might have to be huge and would cause the sense terminal to have a lower voltage.

NOTE AGAIN I didn’t mention anything with the sense line and a diode.

The simplest way to reduce current is to place a high current diode in the CHARGING circuit and sense on the alternator side ( that’s even assuming your doing battery sensing which most people’s setup are not anyway. ) a splitter diode in effect achieves this and could be wired to provide two diode drops, this lowers the potential charge voltage and hence limits the alternator current

It’s not a perfect solution but it’s simple and conventional splitters will have the required rating.

[goboatingnow]

Placing a dry cell in the sense line could have an entirely arbitrary effect it could cause the regulator to shut down the field current almost completely.

You really need to know the precise alternator regulation point , ie 12.8 ( FePO4) plus 1.5 V might still be below the set point of the alternator.

I would not advise that method be used. ( nor is it long term sustainable)