Fewer parallel cells in the battery pack. Better DC air conditioner options. Lower current for easier/cheaper BMS selection.
Experiences charging LFP from alternator WITHOUT a DC-DC charger
- Thread starter Dzl
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How about this unit? https://www.mastervolt.com/products/charge-mate-to-connect-two-batteries/charge-mate-pro-90/. It says that you can parallel them for more current. Can use the BMS to control the on/off switch. Two birds with one stone?
I believe that's just current limiting. Without a boost dc-dc circuit I don't see the point.
If there is sufficient voltage by the time you get to the house batteries, you could use the BMS to control the relay and prevent overloading your alternator with a single unit. Can use 2 of them for 180a max and not nearly as expensive and current limiting as dc to dc solutions. It may take a boost to overcome the drop but I'm going to have to measure it to know for sure.
You need very low resistance to get 180a above like 13v SOC (which is pretty low) without some sort of voltage boosting, there just isn't enough of a potential difference. Sure you can protect your alternator from the worse case scenario of a fully discharged battery, but I'm not convinced that's actually necessary and if it is do I need to spend more than the alternator is worth to protect it? On a boat out at sea I can see the want to play it safe, a vehicle though?
What I was thinking of doing previously was having two relayed connections B2B, one direct, the other with a inline resistor to handle the worst case. It would be pretty easy to fire the direct one most the time but disable that and fire the extra resistance one below say 13V. Ideal constant current? no, but it's like $20 of parts. But this thread has convinced me not even to do that.
I can see the case for an external regulator or a high current dc-dc device with voltage boost, or even a current limiting only device where that is all that is needed, but a large current limiting only device seems silly.
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That's fair and I agree. I think the heavy-duty alternators in these trucks are made for big loads with long duty cycles. The questions are: How much voltage will you see at the house battery? How will the alternators perform with LiFePO4 at very low SOC? My truck is across the state having the camper shell mounted so I can't test it right now. When I get it back, I'll mock it up and simulate a load and measure the temp at the alternator. I'd love it if someone else gave it a shot and let me know how it went, though 
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Bzzzt
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I like the idea of having a resistor reserved for worse case scenarios. If there actually is a danger of overloading the alternators (endlessly debatable) it only exists between 0 and maybe 10% state-of-charge. After this the rising battery voltage should limit the amps to a reasonable level. If you are being reasonably careful with your batteries you should be able to avoid these low SOC situations though - so you are right that this is probably unnecessary.
Likewise - the voltage boost is only really required if you insist on maintaining the maximum charge rate between 90 and 100% state-of-charge.
Between 15-90% state-of-charge the LiFePO4's voltage and flat voltage profile is almost as good as it gets for unregulated charging from a 14.4 volt source! Whether you get 100 amps or 200 amps depends entirely on how scrupulous you are about wiring and connections.
This was one of my big reasons for selecting the electrodacus BMS, It's pretty easy to program the outputs to do stuff like this if I need to (direct connect disconnect below 13v for alternator protect, disconnect both above 14v for the charging shutoff). I was originally thinking 2 Overkill BMS's (to get 200a capability) + an arduino setup to enable/disable stuff, but the electrodacus can do all that (with no max current limitation!).
As for the need of that in my truck I still don't know, but I should have enough stuff to start alternator testing and determining my resistance to where the pack will be this weekend. Full install is probably a month or two out still as I'm waiting on battery cells and then I'll need to build the packs however (I have a LOT to build besides the electrical and work + fam as well). I did get factory workshop manuals in yesterday (2007 Expedition EL) and I don't see a temp sensor for the alternator specifically, but do now know the ECU monitors and sets the target alternator voltage and does stuff like idle up to meet draw if needed and temperature is a factor (cold lead battery needs higher voltage apparently). So even this 14 year old truck has a fairly sophisticated alternator setup.
This thread is getting long, but Bzzzt has posted his results and Luthj and a few others have added their experiences. Besides tales of woe from the marine we haven't had any horror stories of exploding alternatorsThat's fair and I agree. I think the heavy-duty alternators in these trucks are made for big loads with long duty cycles. The questions are: How much voltage will you see at the house battery? How will the alternators perform with LiFePO4 at very low SOC? My truck is across the state having the camper shell mounted so I can't test it right now. When I get it back, I'll mock it up and simulate a load and measure the temp at the alternator. I'd love it if someone else gave it a shot and let me know how it went, though
Getting off-topic and I have not researched AC much, but what options are way better than the Cruise N Comfort stuff? The HD-12L 8K unit (which is somewhat split) is listed as 42 nominal amps @ 12.8 Volts DC on low, 49A on high, so where you getting 78A? It's hard to see how one style AC system could be drastically better than another for a particular BTU rating (with the exception of bad designs like those dumb portable AC units that only blow hot air out the window).
There is a pretty big difference in COP (coefficient of performance) for various designs. Mini splits often use 30-70% less power for the same cooling output than compact/RV units, and are much quieter doing it.
You should also make sure the conditions used for the ratings are equal, as not all manufacturers use the same conditions.
You should also make sure the conditions used for the ratings are equal, as not all manufacturers use the same conditions.
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Its a matter of space, if you have it, the mini splits are a great option. There are euro (220V) models that are ~30 SEER (4 COP). Almost worth a dedicated inverter!
There are some inverter 8k BTU window units which could be used with a powered duct/fan over the shroud (for inside a trailer or RV).
There are some inverter 8k BTU window units which could be used with a powered duct/fan over the shroud (for inside a trailer or RV).
This thread was sidetracked into discussion of air conditioning in the end but I’d like to revive it. I learned a lot.
In the attachment a Victron distributor shows two devices to charge house batteries from an alternator as part of integration as backup into an All In One. It probably assumes lead acid batteries. For a standard alternator the Cyrix is recommended which, in it’s lead acid to LFP version, is Cyrix-Li-ct at either 120a or 230a: https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf
For a “smart” alternator (in the UK the “smart” alternator is known as a “Euro5/6) the Orion DC to DC devices are recommended: https://www.victronenergy.com/uploa...Smart-DC-DC-chargers-isolated-250-400W-EN.pdf. They appear to max out at 360 watts however.
To steer this conversation in a selfish direction I have a Prius Prime. The Prime has DC to DC converter which replaced the alternator. The converter apparently has a max of about 100 amps (fused at 125a). The Prime has a 12v flooded lead acid battery in addition to the traction battery.
The Cyrix amperage appears potentially too high. The Orion lower than I prefer. I realize there are other manufacturers.
If I want to charge an LFP from the Prime which of these should I choose? And it appears some have at least imagined using direct cables perhaps with proper monitoring and a resistor to manage excessive amperage?
Happy for further updates on what has been tried. Here is video if anyone is interested in how the Prius eliminated the alternator:
In the attachment a Victron distributor shows two devices to charge house batteries from an alternator as part of integration as backup into an All In One. It probably assumes lead acid batteries. For a standard alternator the Cyrix is recommended which, in it’s lead acid to LFP version, is Cyrix-Li-ct at either 120a or 230a: https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf
For a “smart” alternator (in the UK the “smart” alternator is known as a “Euro5/6) the Orion DC to DC devices are recommended: https://www.victronenergy.com/uploa...Smart-DC-DC-chargers-isolated-250-400W-EN.pdf. They appear to max out at 360 watts however.
To steer this conversation in a selfish direction I have a Prius Prime. The Prime has DC to DC converter which replaced the alternator. The converter apparently has a max of about 100 amps (fused at 125a). The Prime has a 12v flooded lead acid battery in addition to the traction battery.
The Cyrix amperage appears potentially too high. The Orion lower than I prefer. I realize there are other manufacturers.
If I want to charge an LFP from the Prime which of these should I choose? And it appears some have at least imagined using direct cables perhaps with proper monitoring and a resistor to manage excessive amperage?
Happy for further updates on what has been tried. Here is video if anyone is interested in how the Prius eliminated the alternator:
Attachments
To be sure I understand the question. You have a Prius prime, with a built-in DC-DC device, and you want to charge Lifepo4 with it. You want to know if you should use a Cyrix switch, or an Orion DC-DC charger.
These are 2 completely different devices. First, what is the voltage output of the Prime DC-DC?
Is the voltage output sufficient to charge Lifpo4? If it is too low (12V-13.8V) then you must use the Orion or something like it to boost the voltage. Yes, this would limit your current, probably more than you like. You can install them in parallel to get more output current.
If you have sufficient voltage, and you also have a Victron battery and BMS, then you might be able to use use the Cyrix. It isn't clear in the datasheet if the Cyrix will work with other than a Victron BMS. Also, you might need to limit current. A lifepo4 could easily pull more than 100A and overload the Prime output. In that case, you are back to the Orion, which will limit current to 30A.
To be clear, the Orion will limit current to 30A. The Cyrix is not a limiting device, so you need to otherwise limit current to not exceed it's specs or the specs of the prime.
Most likely, the Orion would be the better option. Two of them would give you 60A, which is a good output if you have 100A available.
These are 2 completely different devices. First, what is the voltage output of the Prime DC-DC?
Is the voltage output sufficient to charge Lifpo4? If it is too low (12V-13.8V) then you must use the Orion or something like it to boost the voltage. Yes, this would limit your current, probably more than you like. You can install them in parallel to get more output current.
If you have sufficient voltage, and you also have a Victron battery and BMS, then you might be able to use use the Cyrix. It isn't clear in the datasheet if the Cyrix will work with other than a Victron BMS. Also, you might need to limit current. A lifepo4 could easily pull more than 100A and overload the Prime output. In that case, you are back to the Orion, which will limit current to 30A.
To be clear, the Orion will limit current to 30A. The Cyrix is not a limiting device, so you need to otherwise limit current to not exceed it's specs or the specs of the prime.
Most likely, the Orion would be the better option. Two of them would give you 60A, which is a good output if you have 100A available.
Thanks @wholybee . Output is 14v. The Cyrix devices do have an amperage limit of 120 amps but the phrase “Continuous current and breaking capacity at 12V or 24V” probably means you destroy the equipment at that point. https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf
It appears there are no devices under $100 which limit amperage to around 50-70amps when a 12v lead acid and depleted 12v LFP are connected together. Does that seem right?
Interesting the folks at Lion say this: https://lionenergy.com/products/lion-safari-ut-1300
“Can I charge from an alternator: Yes, the Safari UT will take too much current so you must limit it with the wire you use to charge it. For example, if you need 10-12 feet of wire, a 10-12 gauge wire will work to limit the current. Double check the actual current with a current meter and size the fuses appropriately. You may need to add fuses and other protective equipment to protect the system. To prevent possible damage to your alternator we recommend using the Redarc (Model #BCDC1225D), which is a DC-DC charger. It will safely charge your batteries while you are driving.”
I’m not intending to simultaneously charge and drive so this makes it sound like if I can get the wiring size right and use proper fuses that might suffice?
It appears there are no devices under $100 which limit amperage to around 50-70amps when a 12v lead acid and depleted 12v LFP are connected together. Does that seem right?
Interesting the folks at Lion say this: https://lionenergy.com/products/lion-safari-ut-1300
“Can I charge from an alternator: Yes, the Safari UT will take too much current so you must limit it with the wire you use to charge it. For example, if you need 10-12 feet of wire, a 10-12 gauge wire will work to limit the current. Double check the actual current with a current meter and size the fuses appropriately. You may need to add fuses and other protective equipment to protect the system. To prevent possible damage to your alternator we recommend using the Redarc (Model #BCDC1225D), which is a DC-DC charger. It will safely charge your batteries while you are driving.”
I’m not intending to simultaneously charge and drive so this makes it sound like if I can get the wiring size right and use proper fuses that might suffice?
@wholybee here is one more option. Victron sells an Argo Diode Battery Combiner. https://www.victronenergy.com/upload/documents/Datasheet-Argo-Diode-Battery-Combiners-EN.pdf
If, instead of connecting two batteries to a DC load, you connected the lead acid to the DC load of the depleted LFP would the device limit the amperage to the 40 or 80 amps (leaving out the “combining” battery altogether)? Surely that won’t work right? ($50 being a lot more attractive than $300.)
This would be only for temporary recharging and not permanently wired.
If, instead of connecting two batteries to a DC load, you connected the lead acid to the DC load of the depleted LFP would the device limit the amperage to the 40 or 80 amps (leaving out the “combining” battery altogether)? Surely that won’t work right? ($50 being a lot more attractive than $300.)
This would be only for temporary recharging and not permanently wired.
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Bzzzt
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This is the way I do it and it has handily kept the current around 70-80 amps into a 240Ah battery. It's trial and error as far as the wiring goes. I think one thing to keep in mind is that if you draw the batteries right down, say to 12 volts, the initial charging current could be quite high (I have seen 160 amps).
No the argo diode combiner will not limit current. If you exceed its rated current, you will damage it.
If you are going to charge from the 14V Prius supply, I strongly recommend the DC-DC charger solution. Renogy make a 20A charger for $119, not to much more than your $100 target. 60A is $233. There are better brands, but that is the budget solution. It solves several issues, not just over current. It charges the Lithium battery with a correct charge profile. It protects alternators from BMS disconnect. I don't know if anything in the Prius would be damaged by a BMS disconnect, but I am sure if it is damages it would be a really expensive fix.
Some people to use undersized wire to limit current. It does work for a low tech answer. I am not in favor of that, as I believe it to be a fire hazard. Lifepo4 batteries are expensive. Your Prius was expensive. It just doesn't seem prudent to save a few dollars of safety.
If you are going to charge from the 14V Prius supply, I strongly recommend the DC-DC charger solution. Renogy make a 20A charger for $119, not to much more than your $100 target. 60A is $233. There are better brands, but that is the budget solution. It solves several issues, not just over current. It charges the Lithium battery with a correct charge profile. It protects alternators from BMS disconnect. I don't know if anything in the Prius would be damaged by a BMS disconnect, but I am sure if it is damages it would be a really expensive fix.
Some people to use undersized wire to limit current. It does work for a low tech answer. I am not in favor of that, as I believe it to be a fire hazard. Lifepo4 batteries are expensive. Your Prius was expensive. It just doesn't seem prudent to save a few dollars of safety.
Thanks @wholybee. I don’t feel need of the precise profile as this would only be for emergency use. My challenge with the 20a charge is that it is hardly more watts than I can pull off a cigarette lighter. I’m hoping for at least .5-1C charge rate and the car can “spare” something like 80 amps (it is fused at 125). I didn’t realize this would be so difficult and costly.
Thanks for offering your knowledge here. Happy for any additional information from you or others. Thanks @Bzzzt.
Thanks for offering your knowledge here. Happy for any additional information from you or others. Thanks @Bzzzt.
@wholybee sorry to both you again. I’m guessing this doesn’t work either?
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