Low cost method to charge LiFePo4 from alternator?

[Franziska]

Hi,



we have a great working low budget LiFePo4 system on-board and are very happy with it.

This forum was a tremendous help in developing it.



We have been asked a number of times about details by other people who like to copy ours.

One question which arises frequently though we can not answer, because it does not apply to us. How to charge safely with an alternator without burning it.

This does not apply to us because we only have outboards and no alternators.


I am therefore wondering if there is a good working low budget method to feed the current supplied by the alternator efficiently to the charging bus bars which are in turn connected to the BMS.



If yes what's the best practice? I like to stress, I'm after a simple, low cost system which does the job without being overly complex.


Chinese components from Alibaba or the like are ok (our current system uses this stuff for several years while living full time cruising), please do not suggest high end stuff from Victron or the like.



Thank you for sharing your wisdom.

[wholybee]

Options:
1) Some factory alternators do have a temperature sensor built in. Those are fine. I can't recommend which. Adding an APD is recommended, but not everyone does it, and the risk is low if you don't (but there is risk).

2) Connect the Alternator to the engine starting battery, and use a DCDC charger between the starting battery and LFP. No APD needed.

3) Like 3, but instead of a DCDC charger, use a long and slightly undersized wire. The wire will get warm and limit current to protect the alternator. The Lead Acid will protect from load dumps. This is often called "hybrid" and there are many arguments about it. I am on the side of "Don't do it." But lots of people do with success.

[newhaul]

Originally Posted by Franziska

Hi,



we have a great working low budget LiFePo4 system on-board and are very happy with it.

This forum was a tremendous help in developing it.



We have been asked a number of times about details by other people who like to copy ours.

One question which arises frequently though we can not answer, because it does not apply to us. How to charge safely with an alternator without burning it.

This does not apply to us because we only have outboards and no alternators.


I am therefore wondering if there is a good working low budget method to feed the current supplied by the alternator efficiently to the charging bus bars which are in turn connected to the BMS.



If yes what's the best practice? I like to stress, I'm after a simple, low cost system which does the job without being overly complex.


Chinese components from Alibaba or the like are ok (our current system uses this stuff for several years while living full time cruising), please do not suggest high end stuff from Victron or the like.



Thank you for sharing your wisdom.

Simplest in my opinion is a dc2dc charger.

[Franziska]

Originally Posted by wholybee

Options:
1) Some factory alternators do have a temperature sensor built in. Those are fine. I can't recommend which. Adding an APD is recommended, but not everyone does it, and the risk is low if you don't (but there is risk).

2) Connect the Alternator to the engine starting battery, and use a DCDC charger between the starting battery and LFP. No APD needed.

3) Like 3, but instead of a DCDC charger, use a long and slightly undersized wire. The wire will get warm and limit current to protect the alternator. The Lead Acid will protect from load dumps. This is often called "hybrid" and there are many arguments about it. I am on the side of "Don't do it." But lots of people do with success.

Thank you!



1)
APD = Alternator Protection Device? Can you please confirm and perhaps recommend/suggest one which does not cost a fortune?

2)
a)
Will the LiFePo4 not destroy the starter battery by sucking a huge amount of juice out of it in short time?
Afaik, LiFePo4 takes as much as it can get.
b)
LiFePo4 have a higher charging voltage and max voltage when full then a typical lead acid starter battery. Does that not mean the LiFePo4 will not get charged up to 80-90% when charged via the lead acid battery?
Or, does the DC-DC charger increase the voltage to achieve this?
Any thoughts on a very reasonable priced suitable charger?
c)
If charging this way, does it matter how big the starter capacity in relation to the size of the LiFePo4 battery capacity?

3)
Interesting, but sounds like it could be a bit risky. So personally I would likely avoid to go down that path.

[PippaB]

Originally Posted by Franziska

T..
2)
a)
Will the LiFePo4 not destroy the starter battery by sucking a huge amount of juice out of it in short time?
Afaik, LiFePo4 takes as much as it can get.
b)
LiFePo4 have a higher charging voltage and max voltage when full then a typical lead acid starter battery. Does that not mean the LiFePo4 will not get charged up to 80-90% when charged via the lead acid battery?
Or, does the DC-DC charger increase the voltage to achieve this?
Any thoughts on a very reasonable priced suitable charger?
c)
If charging this way, does it matter how big the starter capacity in relation to the size of the LiFePo4 battery capacity?
...

a) since LFP voltages, even when deeply discharged, are higher than lead-acid it is the other way around, the LFP tends to charge the lead-acid battery, and keep its voltage high. If the alternator is charging both the the voltage is equal and the current goes to whatever will accept it (usually the LFP). But, that is for a direct connection, the recommendation is for a DC-DC charger between start and LFP. The DC-DC isolates the two batteries and handles the voltage differences.

b) yes, the DC-DC changes the voltage on the output side to match what is needed for that battery. On the input side it monitors the voltage and charges the output side when the input side is over 'x' - it uses the voltage on the input side to detect when the alternator is running, say at 13.4V or something in that area, and only activates charge to the LFP when the input voltage indicates the alternator (or solar, or whatever charge source) is running.

Absolutely no knowledge, but a quick search yields this:
https://www.alibaba.com/product-deta...337759482.html

c)no, not really. Starter and house banks are usually quite different in size. What matters is alternator size and DC-DC size. No point in putting an 80A DC-DC on a 40A alternator. You do want the DC-DC to be able to handle the maximum real-world alternator output so you can minimize run time of the engine. A little care has to be used with selection to make sure you can limit the DC-DC draw to that with which the alternator is comfortable, otherwise it will draw as much as the LFP will take (which, as you say, is a lot).

[Franziska]

Great answers!

Thank you!

Any more recommendations to specific DC-DC chargers (or brands) someone used successfully?
Especially if the alternator has a high output?


How about this one, if their alternator could deliver 80A:
I just found this on AliExpress:
366,27€ | Battery Charger RVs Boat Car Dual Battery System 12V to 14.6V 40A-80A Lifepo4 Charger 10V to 16V for Lifepo4 Lithium Battery
https://a.aliexpress.com/_EzKvPtL

[Be Free Sailor]

Greetings from Denmark.

I have been using 30A Victron DC-DC charger on several cats over the years, and will use them again on my current project boat.

I get them from SVB
https://www.svb24.com/en/victron-ori...o-12v-30a.html

[Franziska]

Originally Posted by Be Free Sailor

Greetings from Denmark.

I have been using 30A Victron DC-DC charger on several cats over the years, and will use them again on my current project boat.

I get them from SVB
https://www.svb24.com/en/victron-ori...o-12v-30a.html

Thank you. I'm a bit hesitant because Victron is usually not part of a budget solution. Which is what this is about.

Great kit, but usually fairly expensive.

Still, interesting. Could one run several of these in parallel if the alternator can put out more?

Say 2x the 30A units connected on the input side to the lead acid battery which is itself connected to a 60A alternator?

Then connect the two outputs to the charging busbars connected to the BMS?

[Pete7]

Originally Posted by Franziska

Great answers!

Thank you!

Any more recommendations to specific DC-DC chargers (or brands) someone used successfully?
Especially if the alternator has a high output?


How about this one, if their alternator could deliver 80A:
I just found this on AliExpress:
366,27€ | Battery Charger RVs Boat Car Dual Battery System 12V to 14.6V 40A-80A Lifepo4 Charger 10V to 16V for Lifepo4 Lithium Battery
https://a.aliexpress.com/_EzKvPtL

I think that is going to be too big. The output from the outboards is likely to be quite small and there will be a difference between pootling along at crusing revs compared to flat out.

I think you will need to put a battery on one of the outboards for a short time and measure the volts and Ah at different revs to see what the effect it. One of thos temperature guns could be useful too, though appreciate this means lifting the outboard hood.

Pete

[wholybee]

Originally Posted by Franziska

Thank you. I'm a bit hesitant because Victron is usually not part of a budget solution. Which is what this is about.

Great kit, but usually fairly expensive.

Still, interesting. Could one run several of these in parallel if the alternator can put out more?

Say 2x the 30A units connected on the input side to the lead acid battery which is itself connected to a 60A alternator?

Then connect the two outputs to the charging busbars connected to the BMS?

Yes, APD == Alternator protection device. AFAIK, there are only 2 popular ones. Sterling and Balmar. The Balmar is under $100, which is cheaper than most DCDC chargers.

Victron is of course preferred. I have a Renogy DCDC. Renogy is often spoken ill of as being a POS, but I think most of that is from people that refuse to use other than Victron. I love Victron and all of my solar is Victron. The Renogy DCDC was cheaper, 60A, and selectable via a switch to 30A. So I have a switch Off/30A/60A, and really like that ability. It works fine and I have no complaints.

[Franziska]

Originally Posted by Pete7

I think that is going to be too big. The output from the outboards is likely to be quite small and there will be a difference between pootling along at crusing revs compared to flat out.

I think you will need to put a battery on one of the outboards for a short time and measure the volts and Ah at different revs to see what the effect it. One of thos temperature guns could be useful too, though appreciate this means lifting the outboard hood.

Pete

Thank you. Nothing to do with our outboards. It's not for us!
I'm asking for people who like our LiFePo4 setup, but do have Diesels and alternators and like to use them.

[Pete7]

Originally Posted by Franziska

Thank you. Nothing to do with our outboards. It's not for us!

Oh, oops missed that bit. In that case the cheapest way is the long wire route. You need a temperature gauge to ensure the alternator isn't getting to hot.

Worth popping over to the 12v FB group, they have a lot of experience of the long wire route.

https://www.facebook.com/groups/144684286108763

[Franziska]

Originally Posted by Pete7

Oh, oops missed that bit. In that case the cheapest way is the long wire route. You need a temperature gauge to ensure the alternator isn't getting to hot.

Worth popping over to the 12v FB group, they have a lot of experience of the long wire route.

https://www.facebook.com/groups/144684286108763

Thank you. I let people know who want to go down that path.



Personally I think I would use the DC-DC method. Not sure I like a wire getting warm/hot on my boat, even if it's in a controlled manner.



As I'm not on Facebook, I can unfortunately not read the details. Still, possibly interesting.

[Pete7]

Originally Posted by Franziska

Personally I think I would use the DC-DC method. Not sure I like a wire getting warm/hot on my boat, even if it's in a controlled manner.

A DC>DC for us too because it gives more control over what is happening. The Victron one can be switched on and off via the app on a smart phone which is nice if your at the wheel coming into a harbour.

Pete

[Franziska]

Originally Posted by Pete7

A DC>DC for us too because it gives more control over what is happening. The Victron one can be switched on and off via the app on a smart phone which is nice if your at the wheel coming into a harbour.

Pete

Hmm. Why would it be important to switch it off when coming into port?