How to not blow up your alternator when charging lithium batteries

[Grinchy]

I found this thread immensely useful and practical. Created an account just to say thanks!
I'm replacing a SLA in an car with an LTO and want to use battery for starting and regular key off draws. Willing to give up some efficiency for simplicity. Have run with the idea above to create a series resistor from an M5 machine bolt, I think this a more practical solution than using a DC DC charger.

[GordMay]

Greetings and welcome aboard the CF, Grinchy.

[Grinchy]

Thanks for the welcome.
Would the small value resistor (0.005 ohm) go before the battery terminal (like a shunt would) or in-line on the alternator positive.
Accessories will be on the shared positive where alternator and battery positive both terminate.
If the resistor is on the battery side than small efficiency loss both in and out of battery. If it’s on the alternator I will need to reterminate the alternator.
Thoughts?

[sy_gilana]

Yandina....Long time no see!

[YANDINA]

Originally Posted by Grinchy

Thanks for the welcome.
Would the small value resistor (0.005 ohm) go before the battery terminal (like a shunt would) or in-line on the alternator positive.
Accessories will be on the shared positive where alternator and battery positive both terminate.
If the resistor is on the battery side than small efficiency loss both in and out of battery. If it’s on the alternator I will need to reterminate the alternator.
Thoughts?

It would be in series with the positive battery terminal. If you can restrict it to incoming current that would be preferable. If you can't there will be a slight voltage drop on outgoing current however since the Lithium battery has a higher voltage anyhow, it should be no problem.

Hi Sy. I've been landlubberated for many years now.

For concerns about the BMS disconnecting due to maximum voltage I doubt that is a problem. The worst risk of damage to an alternator is if it is disconnected when putting out maximum amps - - although the regulator cutoff is instant, it takes too long for those heavy magnetic fields to dissipate causing a voltage spike. But at 14.6 +/- the output current is so small the risk of a voltage spike is negligible.

HOWEVER if the BMS shuts off due to over-current while charging that would be a problem. Fortunately it is unusual for your alternator to have an output higher than your BMS.

I suspect too, that with the drop in price of high voltage rectifiers in the last 30 years there is minimal $ saving using low voltage diodes and alternators are much more robust now days.

[mbartosch]

Originally Posted by Grinchy

Would the small value resistor (0.005 ohm) go before the battery terminal (like a shunt would) or in-line on the alternator positive.

Accessories will be on the shared positive where alternator and battery positive both terminate.

If the resistor is on the battery side than small efficiency loss both in and out of battery. If it’s on the alternator I will need to reterminate the alternator.

I don‘t get the idea behind the resistor. (And I am an EE).

In order to protect an alternator charging a battery based on a lithium chemistry you will need to limit the heat the alternator dissipates, either by limiting the charging current to a fixed maximum value (often implemented via a DCDC charger) or by monitoring the alternator temperature and regulating the field current accordingly.
You will also have to protect the bridge rectifier between alternator and battery from a voltage surge which happens if a load on the charging alternator is suddenly dropped by the BMS.
Neither can be done (properly) by a series resistor.

[goboatingnow]

I think two things are being mixed up

HVC disconnect typically ( note typically )occurs under low current situations hence the load dumping spike will be unlikely to damage the alternator regulator

The other is over stressing the alternator while charging lithium’s , this is best controlled by temperature limiting the alternator output.


It should be pointed out that modern automotive alternators are typically protected and limit load dumping to 35V/40V . ( ie ISO 7637-2 test conditions ) Without such protection typically you can get 80 V or more and this can last for up to 40-60 mS ( which is the real protection challenge )

Automotive electronics properly rated are designed to handle such events as well as battery reversal etc.

Never the less of the risk of complete alternator disconnect exists it would be better

(A) to have remote field shutdown of the alternator from the BMS

Or

(B) provide a substitute load. This could be a resistor like you say or sometimes others suggest a lead acid battery left in circuit.

I am a retired EE with sone experience in this area

The main issue with load dumping is protecting all the other electronics not the alternator in my experience , too much marine electronics is not qualified to withstand such events , ie designed to ISO 7637-2 or SAE J1113-11

[Dan Kimblad]

Originally Posted by DeepFrz

I came across this video posted by Victron Energy and thought it might be of interest to our members.

Thnx
That video was great.
It convinced me even more that I have done the right thing.
Since two year I use a water cooled alternator whit a heat exchange from sea water to the internal system only running for the alternator and charge 140 Amp at idling. I have measured up the internal temperature to 47 Celsius inside the alternator. IF i could lower that one even more then the charge Amp will rise up.

https://www.youtube.com/watch?v=6xjsDT2OuV4

I have change the ratio to 1:3,15 so my tacho is showing too much. But thats only a number.

[randydandy]

What would be wrong with having the alternator charge the starting bank of AGM's and a DC to DC charger from the starting bank to the house bank? It seems to me if you have a 120 or even a 140 amp alternator, your not really losing much if any by using a 60/80 amp dc to dc charger. I'm willing to bet that most here either use a standard duty alternator or a "heavy duty" alternator with maximum current ranging from 80-140 amps. At best these alternators only want to put out 2/3 of the maximum current continuously at idle. So I'm not sure your losing anything by installing a 60 or 80 amp dc to dc charger. Not to mention, most Lithium battery's don't want to charge faster than 50 amps on a single LIPO4 100ah. Of course most will have a larger bank. It seems the sweet spot is about 60-80 amps for a 200-400ah bank.

[goboatingnow]

Look into the costs of a 80A dc dc charger !!!

Easier to just go for an external regulator and properly control the alternator.

Standard alternator regulators are not designed to charge batteries, whether Lead acid or lithium. They are designed to act as a constant voltage power source for the cars electrical needs.

[Networker]

Originally Posted by randydandy

What would be wrong with having the alternator charge the starting bank of AGM's and a DC to DC charger from the starting bank to the house bank? It seems to me if you have a 120 or even a 140 amp alternator, your not really losing much if any by using a 60/80 amp dc to dc charger. I'm willing to bet that most here either use a standard duty alternator or a "heavy duty" alternator with maximum current ranging from 80-140 amps. At best these alternators only want to put out 2/3 of the maximum current continuously at idle. So I'm not sure your losing anything by installing a 60 or 80 amp dc to dc charger. Not to mention, most Lithium battery's don't want to charge faster than 50 amps on a single LIPO4 100ah. Of course most will have a larger bank. It seems the sweet spot is about 60-80 amps for a 200-400ah bank.

I have 1500ah, so a DC to DC charger doesn’t work. I do have one, but it’s for the lithium bank to charge the starter battery.

To protect the alternator, I simply added a Sterling Alternator protection device for $100 to the mix. I’ve been toying with the idea of also adding a lead battery to the lithium bank, that way if somehow the lithium went out, the lead would take the charge and protect the alternator, and act as a quick backup.

[randydandy]

Originally Posted by Networker

I have 1500ah, so a DC to DC charger doesn’t work. I do have one, but it’s for the lithium bank to charge the starter battery.

To protect the alternator, I simply added a Sterling Alternator protection device for $100 to the mix. I’ve been toying with the idea of also adding a lead battery to the lithium bank, that way if somehow the lithium went out, the lead would take the charge and protect the alternator, and act as a quick backup.

Good call. I've got a 600ah battery with (2) dc to dc chargers charging the house from the start bank. We had a number of things to do to the boat and this was an easy way to get this part of the refit partially completed. Sometime next year I'll probably get all of the wiring sorted out, install an alternator protection device, and charge the house directly. Is the Sterling device sacrificial in any way?

[Networker]

Originally Posted by randydandy

Good call. I've got a 600ah battery with (2) dc to dc chargers charging the house from the start bank. We had a number of things to do to the boat and this was an easy way to get this part of the refit partially completed. Sometime next year I'll probably get all of the wiring sorted out, install an alternator protection device, and charge the house directly. Is the Sterling device sacrificial in any way?

It is indeed sacrificial, and I should carry a spare. The wakespeed is the traffic cop that keeps the chaos to a minimum. The Sterling is the insurance policy.

[randydandy]

Originally Posted by Networker

It is indeed sacrificial, and I should carry a spare. The wakespeed is the traffic cop that keeps the chaos to a minimum. The Sterling is the insurance policy.

Good to know. I've got a Balmar MC-614 regulator and figuring out how to program that thing is another one of my hurdles. I understand the Wakespeed uses an app and bluetooth?

[Networker]

Originally Posted by randydandy

Good to know. I've got a Balmar MC-614 regulator and figuring out how to program that thing is another one of my hurdles. I understand the Wakespeed uses an app and bluetooth?

I had the MC618 and I know it has a Bluetooth option, as well as a magnetic pen option. Not sure about the 614 though.

The wakespeed has an app (however, only the Android version can upload a configuration so I question the usefulness of the iPhone app), but shockingly it does NOT have a Bluetooth option! You need an esoteric USB cable from the android phone to the wakespeed to program it. Or use a laptop and their basic terminal language which is a bit too much for me to want to learn.


Steve


Steve