Experiences Charging LFP (LiFePO4) from altnerator without a DC-DC charger

[dzl_]

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring advised methods and hoping for the best.


Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

[BeNimble]

Originally Posted by dzl_

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring advised methods and hoping for the best.


Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

I use a LiFePo 4-cell battery as the "house" battery in my Prius that replaces the lead-acid battery. Works just fine, used it for years, out lasted the prius put it in another prius.
Now note the prius has a dc-dc converter to charge the lead acid, not an alternator, but it outputs 14.2 volts so good enough for the lfp, in fact maybe better that it undercharges it.

[cadillackid]

I don’t have experience with lfp but now that I’ve been playing with batteries and chargers I can say that my alternator never charges my AGM fully .. even with a long drive, I put it on the Victron charger designed for AGM and they take quite a bit more.

But with lfp that might be beneficial ? My chevy volt battery was supposedly never charged above 85 or 90 percent. Seems ll like you’d be OK?

[dzl_]

Originally Posted by cadillackid

I don’t have experience with lfp but now that I’ve been playing with batteries and chargers I can say that my alternator never charges my AGM fully .. even with a long drive, I put it on the Victron charger designed for AGM and they take quite a bit more.

But with lfp that might be beneficial ? My chevy volt battery was supposedly never charged above 85 or 90 percent. Seems ll like you’d be OK?

The added complexity with LFP (in my limited understanding) is:
(1) lithium batteries have exceptionally low internal resistance, this means they will take as many amps as you can throw at them, exceeding the alternators abilities. So your alternator will break its back trying to supply the battery bank and may meet an early death due to heat.
(2) with a BMS the battery can be suddenly disconnected. Not sure if this would be a problem or not for a house bank. I believe it would be a potential problem if it were the only battery in the system. Not sure on this one.


The usual solution is a DC-DC (b2b) charger. But a external regulator is another less common option, a purpose built alternator built for something like an ambulance maybe that is designed for high continuous output might work, im not sure. Hoping to learn from people who have tried one or the other approach.

[cadillackid]

Originally Posted by dzl_

The added complexity with LFP (in my limited understanding is:
(1) lithium batteries have exceptionally low internal resistance, this means they will take as many amps as you can throw at them, exceeding your alternators continuous output. So your alternator will break its back trying to supply the battery bank and may meet an early death due to heat.
(2) with a BMS the battery can be suddenly disconnected. Not sure if this would be a problem or not for a house bank. I believe it would be a potential problem if it were the only battery in the system. Not sure on this one.


The usual solution is a DC-DC (b2b) charger. But a external regulator is another less common option, a purpose built alternator built for something like an ambulance maybe that is designed for high continuous output might work, im not sure. Hoping to learn from people who have tried one or the other approach.

so LFP wont do like my AGM do which is take a really heavy amperage for the first few minutes then level off? ie if i run my batteries down to say 55 or 60% then start the bus , my alternator will hit them (2 group 31s) with 75 amps or so total but will seemingly quickly level off to 45-50 total where they will slowly but surely lower amp draw as the ycharge up.. are you saying an LFP will pull amps hard till it reaches a higher SOC percentage as opposed to roll off like an AGM?



why would your batteries suddenly disconnect? they get too hot from charging and the BMS shuts off?

[john61ct]

The critical factor is **current limiting**

without tht, any sure gets burnt, not just alternators

unless the LFP pack is tiny compare to the source current offered

but then that is very bad for LFP longevity, need to keep the C-rate to 0.4C or so (depends on temperature).

I've used Balmar MC-614 VRs, those let you set the max current rate to a fine degree, better than any DC-DC.

Same with the Wakespeed and American Power Systems based on Al Thomason's original SAR FOSS project.

But if you're taking about an alt in a modern style mpg-conscious vehicle, especially Euro sourced, then that is not an option, to closely integrated with the ECU.

Originally Posted by BeNimble

I use a LiFePo 4-cell battery as the "house" battery in my Prius that replaces the lead-acid battery. Works just fine, used it for years, out lasted the prius put it in another prius.
Now note the prius has a dc-dc converter to charge the lead acid, not an alternator, but it outputs 14.2 volts so good enough for the lfp, in fact maybe better that it undercharges it.

That converter is current limited, nothing to do with source as alternator.

[john61ct]

Originally Posted by cadillackid

so LFP wont do like my AGM do which is take a really heavy amperage for the first few minutes then level off?…
LFP will pull amps hard till it reaches a higher SOC percentage as opposed to roll off like an AGM?

That is exactly correct, completely different behaviour from lead.

Even the best deep cycle AGM cannot pull more than 0.6-0.8C and that for only a short time in early Bulk stage, seven hours before it gets to Full, which it must reach for longevity.

LFP can get to Full in 90min, can easily pull 3-4C which is very bad for longevity, and amps do not start falling until the last few minutes, depending on the actual (throttled) C-rate.

[john61ct]

Originally Posted by cadillackid

why would your batteries suddenly disconnect? they get too hot from charging and the BMS shuts off?

Also unlike lead, LFP longevity is much more sensitive to overcharging

The charge profile should not Float an LFP bank.

Soon as you hit your chosen definition of Full (e.g. 3.45Vpc) the bank should get isolated from the charge source.

In fact, since it is unhealthy for LFP to sit at Full for any length of time

again opposite of lead

you really should not go near Full unless loads are / will soon be ready to start pulling SoC% back down.

And when you won't be cycling for a while, best to pull down to a "storage SoC", around 3.2Vpc at rest.

[john61ct]

Originally Posted by dzl_

with a BMS the battery can be suddenly disconnected. Not sure if this would be a problem or not for a house bank. I believe it would be a potential problem if it were the only battery in the system.

Just ensure a lead battery is in parallel with alternator output

to absorb any "load dump" spikes/surges.

Most just use one already in place as a Starter batt.

But a cheap small one works fine.

There are pricey electronics-based "solutions" also, but I can't imagine a scenario where the extra expense would be justified.

[john61ct]

Originally Posted by dzl_

alternator built for something like an ambulance maybe that is designed for high continuous output

Yes, exactly also fire trucks, some police vehicles, unlike normal units targeted to consumer vehicles, not only actually produce their nameplate rated output, but can do so 24*7 without failing.

Leece Neville 4000 series are just an example.

Often found on eBay for just a few hundred, don't cost much to get reconditioned at a local alt shop, adapted to the (required) external VR

The large frame is what allows the high performance cooling, but may also require some re-engineering in the engine bay, custom serpentine setups, specially sized pulleys etc

All that stuff costs lots more than the alt itself

Compared to a decent solar setup combined with a portable inverter genset may make more sense,

or just adding a good DCDC for a few hundred ends up much more cost effective.

"All of the above" is often really only worthwhile if

high Ah per day usage, and

living off grid many months if the year if not fulltime, and

often travelling, rather than settled down in one spot for weeks.

That last factor is what points to investing in a solid charging from alt setup.

For those needing to weld off grid, also check out Zena's engine-driven welder / 200A alternator , and other apparently similar alternatives based on modding Delco CS-144, or LN's "weldernator" http://news.prestolite.com/content/weldernator

[dzl_]

Thanks John, I was hoping you would weigh in on this when I made the post, figured you might have some insight here.


So with a properly sized alternator, rated for continuous use, the risk to the alternator overheating is mitigated.


But now I'm wondering in this situation (assuming no external regulator or DC-DC charger) what would keep the alternator from exceeding the batteries max continuous charge current (or recommended charge current)

[john61ct]

Originally Posted by dzl_

So with a properly sized alternator, rated for continuous use, the risk to the alternator overheating is mitigated.

No!

it is the current limiting device in between, that prevents the LFP overworking the alt, drawing too many amps.

Even a 250A fire truck alt will get fried without the CL ext VR or a DC-DC.

Going big amps just helps you charge faster, if your bank is big enough that your C-rate stays reasonable low.


> But now I'm wondering in this situation (assuming no external regulator or DC-DC charger) what would keep the alternator from exceeding the batteries max continuous charge current (or recommended charge current

Current limiting is not optional, need it one way or another.

Some combiners (like VSR/ACRs) feature that, e.g. 15A current limit for the EchoCharge and 30A for the DuoCharge, but IMO those are crude instruments not suitable for LFP.

[dzl_]

Originally Posted by john61ct

No!

it is the current limiting device in between, that prevents the LFP overworking the alt, drawing too many amps.

Even a 250A fire truck alt will get fried without the CL ext VR or a DC-DC.

Going big amps just helps you charge faster, if your bank is big enough that your C-rate stays reasonable low.

Ahh okay that makes more sense, I misread/misinterpreted what you were saying about the Leece-Neville and continuous output large frame alternators.


Now it makes more sense.


So to summarize, regardless of alternator, a current limiting device (most notably a DC-DC (B2B) charger or external regulator needs to be used to limit current somehow.


That actually really simplifies things.


Do you see any major advantages to the External Regulator route over the DC-DC route?

[john61ct]

The external VR must include solid CL circuitry, not all do, adjustable current control **while keeping the V setpoint constant** is very rare and pretty darn pricey.

Same with DC-DC converters not sold as "chargers", that CL function is IMO critical to claiming that label with AC-DC rectifiers as well, along with automating the stop-charge function.

Originally Posted by dzl_

Do you see any major advantages to the External Regulator route over the DC-DC route?

External VR obviously can pump higher current rates, would need to stack multiple DCDC in parallel

plus the granular control, can turn the amps down a bit in hotter ambients.

But it's part of the vehicle, hard to transfer - any expensive mod work obviously can't, and with lots of modern computer-controlled vehicles, simply can't be made to work at all

Plus, only helps with the one energy source, the alt.

While the DC-DC conditions the profile from any source, can use an old shore charger, cheap DCDC converter, save money on cheap/dumb solar controllers, wind power etc

can also be seen as a front-end part of the bank, move both to other vehicles, even the most fussy locked down mpg efficient Euro designs

also can move with the pack to use on a boat, camper / trailer, off grid home, so lots more flexibility.

[Rock-N-Ruth]

Originally Posted by dzl_

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring advised methods and hoping for the best.


Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

We have 4 huge BYD 24v LiFeP04 batteries that allow us to live as if we are grid tied even though we never plug in or use the generator. That's right, never. We bought them in pairs, used, paying 880 for the first pair and 950 for the second pair. If we had built the same batteries from new cells our investment would be around 7500 smackers. Now 1830 bucks is a lot of scratch to us poor hillbillies, seriously. It's more than we paid for the bus. Over charging will ruin that investment. Two things gas you dont want to do with LiFeP0 batteries is over charge or charge when to cold.
I would never ignore the recommended charging profile for your LFP batteries. That could be a very costly mistake.
You can take input from your vehicle charging system into a solar charge controller that is configured for your LFP batteries, and it won't know the difference between your alternator and solar panels. Your alternator will just see the solar controller as a load.

[Rock-N-Ruth]

Originally Posted by dzl_

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring advised methods and hoping for the best.


Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

We have 4 huge BYD 24v LiFeP04 batteries that allow us to live as if we are grid tied even though we never plug in or use the generator. That's right, never. We bought them in pairs, used, paying 880 for the first pair and 950 for the second pair. If we had built the same batteries from new cells our investment would be around 7500 smackers. Now 1830 bucks is a lot of scratch to us poor hillbillies, seriously. It's more than we paid for the bus. Over charging will ruin that investment. Two things you dont want to do with LiFeP0 batteries is over charge or charge when to cold.
I would never ignore the recommended charging profile for your LFP batteries. That could be a very costly mistake.
You can take input from your vehicle charging system into a solar charge controller that is configured for your LFP batteries, and it won't know the difference between your alternator and solar panels. Your alternator will just see the solar controller as a load.

[Doktari]

I don’t have experience charging LFP without a DC-DC charger. So far so good with my Kisae Abso 50 amp DC-DC Charger. I hope it lasts. The current limiting is very useful. My belt started to squeal annoyingly so I turned down the current until I can get a new belt installed. I only have a 70 amp alternator so wanted current limiting charging the 200ah LFP battery. It’s a 1996 Chevy G30. I’m wondering if a slightly more powerful alternator is a option?. I’m going to to some testing with my clamp meter to see how much current is pulled running the ignition, lights, blower, fuel pump, etc. I’d also like a temperature sensor on my alternator. Or should it be inside the alternator on the diodes?
Also auxiliary cooling of the alternator might help. Ducting cold air, or maybe a bblower? My vehicle is a van so the engine compartment is hot!

[Doktari]

Originally Posted by Rock-N-Ruth

We have 4 huge BYD 24v LiFeP04 batteries that allow us to live as if we are grid tied even though we never plug in or use the generator. That's right, never. We bought them in pairs, used, paying 880 for the first pair and 950 for the second pair. If we had built the same batteries from new cells our investment would be around 7500 smackers. Now 1830 bucks is a lot of scratch to us poor hillbillies, seriously. It's more than we paid for the bus. Over charging will ruin that investment. Two things you dont want to do with LiFeP0 batteries is over charge or charge when to cold.
I would never ignore the recommended charging profile for your LFP batteries. That could be a very costly mistake.
You can take input from your vehicle charging system into a solar charge controller that is configured for your LFP batteries, and it won't know the difference between your alternator and solar panels. Your alternator will just see the solar controller as a load.

I noted that the manual for my Morningstar Prostar Mppt charge controller says that connecting its input to anything other than solar panels will void the warranty. I know people have connected alternators to Outback and Midnite controllers input in parallel with solar panels and the panels act to clamp the voltage. This can work reliably.
In theory one could use a 24 or 48 volt alternator this way to charge a 24 or 48 bolt house battery. And charge the the starting battery with a dc-dc charger. Has anyone tried this?

[Native]

Originally Posted by john61ct

For those needing to weld off grid, also check out Zena's engine-driven welder / 200A alternator , and other apparently similar alternatives based on modding Delco CS-144, or LN's "weldernator" http://news.prestolite.com/content/weldernator

John, the link you provided gives an SSL (site certificate/encription) error and if that is ignored, the website reports a 404 error (npage not found).

[john61ct]

Thanks for the update, looks like it got discontinued,

checkout the Wayback archive?

lots of DIY howto's on the concept out there.