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Old 04-07-2024, 08:42 AM   #1
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DC to DC regulator

I have just installed two 200 watt solar panels. Now I am thinking of adding a lithium battery. Can I let my regular alternator charge my battery to 80% and then let my solar panels to the rest?
MY question is if i don't use a DC to DC regulator will the Lithium battery draw too much power and destroy my alternator?
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Old 04-07-2024, 02:03 PM   #2
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You need to either change out the BIM (battery isolation manager) for a LiBIM which is a simple swap OR go to a DC2DC charger. I started off my Lithoum swap by switching to the LiBIM but found poor charging from it because itís only charging 40% of the time. I changed to the Victron 12-12-30 DC2DC charger but they have issues with overheating and this degrades the charge rate. Victron has come out with a new totally redesigned 12-12-50 DC2DC charger that is just now starting to become available, should be getting mine any day now. Here is a very good article that explains the pros and cons.

PS, there are getting to be a lot of reports of the LiBIM failing so buyer beware.

https://explorist.life/how-to-charge...le-alternator/
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Old 04-09-2024, 01:06 PM   #3
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Precision Circuits Inc makes a 160 amp Part Number: 00-10041-260 and a 225 amp Part Number: 00-10041-261 LIBIM. Below is a link explaining how they work. Direct replacement for your factory BIM
https://www.precisioncircuitsinc.com...i-BIM-Rev1.pdf
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Old 04-14-2024, 06:59 AM   #4
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DC to DC charger

Thank you, After reading several articles i think i am going to go with the DC to DC charger.
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Old 04-19-2024, 02:01 PM   #5
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The Victron 12-12-50 is finally shipping, just received mine today.
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Old 04-19-2024, 03:36 PM   #6
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The Victron 12-12-50 is finally shipping, just received mine today.
OK Brian, got a question.
We have 185 amp alternators. With a LiBIM the batteries would get 185 amps for 15 minutes, the nothing for 20 minutes and repeat. So at 40% operational that means the batteries are getting (185*.4) about 74 amps per hour. With a DC to DC 12-12-50 don't the batteries get 50 amps every hour?

Or is my math just way off, or my understanding of a DC to DC?
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Old 04-19-2024, 04:47 PM   #7
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OK Brian, got a question.
We have 185 amp alternators. With a LiBIM the batteries would get 185 amps for 15 minutes, the nothing for 20 minutes and repeat. So at 40% operational that means the batteries are getting (185*.4) about 74 amps per hour. With a DC to DC 12-12-50 don't the batteries get 50 amps every hour?

Or is my math just way off, or my understanding of a DC to DC?

Just because you have a 185 amp alternator does not mean that is the charge output that you will be getting to your coach batteries, they say to figure maximum of 70% from your alternator and more like 50-60% as it is running the chassis and itís systems. So if you are lucky to get 110 amps charge rate but only 40-42% of the time you are getting that is not as good at 50amp charge, 100% of the time while causing less wear and tear on the alternator and providing the higher voltage needed to completely charge a Lithium battery to 100%. If you have solar, the Victron DC2DC charger can be set to shut down and let solar do the work as itís networked with all my other Victron components. I have seen about 3 reports now of the Precision Circuits LiBIM failing and two people have now said that Precision Circuits does not recommend the LiBIM if you have over 400ah of Lithium as it canít handle it. If you want a higher rate than the new Victron 12-12-50 or the 12-12-30, they can be paralleled for a higher rating.

Here is a really good article that covers the pros and cons of both methods but I feel the DC2DC charger is the safest most effective way to charge my 1120ah battery bank off the alternator.

https://explorist.life/how-to-charge...le-alternator/
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Old 04-22-2024, 07:57 AM   #8
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I'm beginning to question the repeated assertions on the forums of how the Precision Circuits Lithium BIM works 20 minutes on, 20 minutes off. There is no mention of this at all in the product spec sheet. Instead, it seems to say that it stays on for the first full hour. From the spec sheet:

"The Li-BIM monitors the battery voltage of both the Lead Acid Chassis and Lithium Coach batteries over long periods of time. If it senses a charging voltage, it connects the two batteries together. If the charging system is drastically overburdened, the batteries will be isolated, however, if the Li-BIM sees a long term charging of both batteries it will allow the batteries to remain connected and allow the charging system to do its job. Once the batteries have charged for one hour, the Li-BIM will isolate the batteries to prevent overcharging, and will only reconnect the batteries for charging if one of the batteries drops to approximately 80% charge, and the other is being charged."
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Old 04-22-2024, 09:12 AM   #9
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I'm beginning to question the repeated assertions on the forums of how the Precision Circuits Lithium BIM works 20 minutes on, 20 minutes off. There is no mention of this at all in the product spec sheet. Instead, it seems to say that it stays on for the first full hour. From the spec sheet:

"The Li-BIM monitors the battery voltage of both the Lead Acid Chassis and Lithium Coach batteries over long periods of time. If it senses a charging voltage, it connects the two batteries together. If the charging system is drastically overburdened, the batteries will be isolated, however, if the Li-BIM sees a long term charging of both batteries it will allow the batteries to remain connected and allow the charging system to do its job. Once the batteries have charged for one hour, the Li-BIM will isolate the batteries to prevent overcharging, and will only reconnect the batteries for charging if one of the batteries drops to approximately 80% charge, and the other is being charged."

That is very interesting, perhaps they changed the design? I know that the ad on amazon still states the charge cycle is 15 minutes on 20 off, and that it says it is a frequently returned item.

Also too mention, I looked at the manual just now and also see below what you copied and pasted "The Li-BIM does not guarantee 100% battery charge, but prevents harmful battery charge levels."

I have never been a big fan of these, however what I liked (assuming it would work well enough) is that it would be a drop in replacement and keep the "AUX" start button functional (emergency start). What I didn't like is how it operated, for example if you wanted to charge your LifePo4 Coach batteries to 14.6V that would be impossibly to do if the chassis side was regulated at 13.8V (which is not uncommon) and the other thing I didn't like was that if you have enough LifePo4 capacity (perhaps even just one 100A battery that was low on its charge) that the engine alternator could run at 100% for an extended period of time and the alternator heat generated during 100% output for a long enough period certainly can certainly damage the alternator, I never made a big point about that as what I understood was that there was a timed cycle, but even then 100% on the 100% off and repeat this every 15~20 minutes isn't all that great of a design imo and for sure if the alternator ran at 100% for an hour then that would be even more concerning. I will also add, if I remember correctly Jayco has 80A self resetting breakers on the charge line that would help, but I suspect that it (I think there is two perhaps) would be tripping and resetting often which isn't a good method to regulate the current.

I recommend a DC2DC charger even more so now. ~CA

https://www.amazon.com/Battle-Born-B...ct_top?ie=UTF8
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Old 04-22-2024, 10:01 AM   #10
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A couple of thoughts,,,,
Just because the Alternator is rated at 185A. That does not mean that you will get that in normal use. That is a cold, best case rating. I would expect in normal use the max output would be around 165A.


The higher the demand, the higher the heat load, the lower the output. As the copper stater winding heat up, the higher the wire resistance. The same for the rectifier diodes, and voltage regulator. Electronics do NOT like heat. The more it is stressed the shorter it's lifespan.


As pointed out, the nominal voltage of our charging system is about 13.9 Vdc. Add in Voltage drop, you will NEVER fully charge a LiPo battery bank at this voltage.
When I go LiPo it will be with a DC to DC converter.
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Old 04-22-2024, 10:12 AM   #11
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I am one of those people that like to talk vs read.
I just got off the phone with Danny at Precision Circuits and he said that the Li-BIM goes 15 minutes on and 15 minutes off. Everyone is saying 15/20 which is 42% but 15/15 is 50% of the time.
Still, the more I dig into this, the more I think I am leaning towards a DC to DC, however, I really like having the AUX Start button. I am thinking of just having that button activate a 12VDC coiled relay that has some high amperage contacts on it and just jump both sides of the DC to DC via the contacts.
We will see, I am not switching to lithium until next winter.
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Old 04-22-2024, 10:21 AM   #12
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Just another thought to add to what Rnagel951 shared above. From even a non-electrical standpoint, most alternators have needle bearings inside that will be damaged from too much heat for too long of a time (even other bearing designs can become damaged). So even if the electrical components inside the alternator don't fail on you, the bearings likely will fail given enough time running at 100% output. While there are many different alternators and designs, some having a larger or multiple fans and some having a larger frame (both provide better heat dissipation), as a rule of thumb you really shouldn't use more than around 50% of the alternators rated capacity continuously. ~CA
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Old 04-22-2024, 10:55 AM   #13
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I am one of those people that like to talk vs read.
I just got off the phone with Danny at Precision Circuits and he said that the Li-BIM goes 15 minutes on and 15 minutes off. Everyone is saying 15/20 which is 42% but 15/15 is 50% of the time.
Still, the more I dig into this, the more I think I am leaning towards a DC to DC, however, I really like having the AUX Start button. I am thinking of just having that button activate a 12VDC coiled relay that has some high amperage contacts on it and just jump both sides of the DC to DC via the contacts.
We will see, I am not switching to lithium until next winter.
I started off using the LiBIM but saw poor charging performance out of it and went to the DC2DC charger. Since I already had the LiBIM installed, I just put battery disconnects on the cables to it and installed a toggle switch to cut off the IGN wire and this disables the LiBIM. If there is a case I needed to use the AUX start, all I need to do is turn on the disconnects and flip the toggle switch and I have AUX start. This also gives me a backup in case of issues with the DC2DC charger. You could do this as a backup using the factory BIM as you are not relying on it to charge and tax your alternator. But then again, Lifepo4 are not suppose to be used in a cranking situation because of the heavy draw can damage or shut them down so a better option would be to use a jump box or start the generator and use a battery charger.

If you talk to PC again, I would ask them what the rating is as far as total battery Ah as it’s not in the specs either. On a Facebook Super C group there is a discussion and the LiBIM failing and two comments saying the PC told them it’s is only good up to 400ah of battery and if you have more, a DC2DC charger is a better choice. Personally, I like the Victron DC2DC charger as it is networked to the rest of my system and is controlled by SOC and not voltage which is more accurate for Lithium, I can setup all charging parameters and is fuse protected.

The description on Battleborns website says 15 on 20 off, PC told you 15 on and 15 off so maybe they have changed them.

https://battlebornbatteries.com/prod...ation-manager/
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Old 04-22-2024, 10:56 AM   #14
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I Like the idea "repeach" has regarding a high amperage contractor to retain aux (Oh crap) battery jump functionality. Even if the LiPo battery BMS shutdown the house side if to much current is drawn. It might be enough to get the engine turning. When starting the Max current draw is when first engaging the starter.

Love having a backup plan!
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Old 04-22-2024, 11:15 AM   #15
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Just a thought to add, if you do have or add an AUX start relay which connects the Coach and Chassis battery(s) together, you should take precautions to make sure the DC2DC charger is disconnected or at least disabled when using the AUX start, as with such a wiring configuration, the aux start relay when closed (on) will also be connecting the output and input of the DC2DC charger together. Will this damage the DC2DC charger? I am not sure, but I will say doing that would be very concerning especially if the DC2DC charger is powered\switched ON, and I highly suggest that it would be better not to find out if damage will occur and instead avoid that from happening in the first place. ~CA
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Old 04-22-2024, 11:46 AM   #16
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Just a thought to add, if you do have or add an AUX start relay which connects the Coach and Chassis battery(s) together, you should take precautions to make sure the DC2DC charger is disconnected or at least disabled when using the AUX start, as with such a wiring configuration, the aux start relay when closed (on) will also be connecting the output and input of the DC2DC charger together. Will this damage the DC2DC charger? I am not sure, but I will say doing that would be very concerning especially if the DC2DC charger is powered\switched ON, and I highly suggest that it would be better not to find out if damage will occur and instead avoid that from happening in the first place. ~CA
It could be a concern depending on the DC2DC Charger. On the Victron unit I have, it is fused and internally protected. It auto connect/disconnects based on engine start detection which is set up on a delay for the charging system to fully energize before it starts charging. It can also be wired to a manual switch if needed.
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Old 04-22-2024, 11:51 AM   #17
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...

If you talk to PC again, I would ask them what the rating is as far as total battery Ah as itís not in the specs either. On a Facebook Super C group there is a discussion and the LiBIM failing and two comments saying the PC told them itís is only good up to 400ah of battery and if you have more, a DC2DC charger is a better choice.
...
I did tell him I am thinking about 600 ah of Lithium and he said no problem.

I like your idea of of the disconnect. We will see, again, not until next winter.
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