The above devices have always confused me, particularly in the context of adding LiPO batteries to a motor home. So, the following is my imperfect understanding of how they work and I would appreciate any corrections or expansions of the following. Why? I am about to buy a new Thor Axis which I believe has the Precision Circuits BIM and I want to add LiPO batteries, solar and do something to limit alternator loading. Bear with me as this will be a bit long:
BIRD is an acronym for a Battery Isolation Relay Device or maybe Bidirectional..... Until somewhat recently most were made by Intellitec and consisted of relays and a heavy solenoid (made by Trombetta) that controlled power between the coach and the chassis batteries. It also included a switch to connect the two to start the chassis battery when it was run down by using the coach batteries.
More recently Precision Circuits (reportedly founded by an ex Intellitec employee) developed a better device, a BIM (an acronym for battery isolation manager) that did the same thing, but was mostly solid state except for the solenoid and had better voltage switching criteria. Most newish MHs use this device.
Either work well in isolating and managing the connections to the two battery systems. Neither have current limiting between the two battery systems which isn't necessary with lead acid batteries whose internal impedence and the fixed voltage of the chassis alternator inherently limits charging current from the alternator.
But LiPO batteries have a much lower impedence, at least intially and ultimately need a charging voltage of 14.4-14.6V to allow them to reach full charge (so do FLA batteries btw). The lower initial impedence can overload the chassis alternator if not limited.
So in order to solve the over loading problem, Precision Circuits offers a lithium version of their BIM for a few bucks more than the normal one. According to PC,.it cycles the solenoid connection on and off (how much on and off is confusing in the PC literature) to limit the load on the alternator. But it does nothing for the fixed voltage, typically 13.5-14.0 V of the alternator which is too low for full charging.
Enter DC to DC chargers. In their simplest form they take an input DC voltage and produce a higher DC output voltage. This can work to take the 13.5-14.0 V output of the alternator and convert it to the 14.4-14.6V that the LiPO battery needs. With a bit more circuitry it can load the alternator to produce even more current by presenting it with a lower inpedence. But it needs to be limited otherwise it overloads the alternator.
Victron and maybe others offers a DC to DC charger to resolve both problems, preventing overloading and producing a higher charging voltage. Victron calls theirs the Charge Mate Pro. It limits current to 30 amps for one model and manages the DC voltage output to fully charge a LiPO battery. But how do you hook one of these up to your coach's DC system?
One way would be to splice the device in between the alternator and the BIM or BIRD. This should limit the current and manage the alternator voltage. The one draw back is since DC to DC chargers are not bi directional (it acts like a diode) it will not allow the BIM to start the engine or charge the chassis battery. But apparently the Victron is meant to be installed in place of the BIM or BIRD. It has an ignition input like the BIRD that turns it on when the chassis ignition is on and it has a switch input that lets the coach battery start the chassis engine when its battery is run down. Does it also allow the coach battery to charge the chassis battery when it is in storage? Victron's literature is a bit obtuse on these questions.
Sooooo, I could someone who has actually used a Victron or one of its competitor's DC to DC chargers describe how it is installed and how it dealt with these issues?
My coach did not come from the factory with a B.I.R.D. charging setup, but most do/did.
So when I bought my coach 5 years ago I installed Keyline's Voltage Sensitive Relay (VSR) so my alternator will charge both my engine battery back and my house battery bank.
I have been using Keyline VSR for ~50,000 miles and it has worked flawlessly; and I have been very happy using this device; plus and I think it is cheaper and more reliable than an Intellitec B.I.R.D..
That said, I do not know if using a VSR in conjunction with a LiFe04 (200AH) battery bank will protect he alternator from overheating or not?
So, I emailed Keyline in October... asking if I can just add a LiFe04 to my existing VSR...in parallel with my 420AH-FLA battery bank; and they said: "Yes, it will work." However, I'm still skeptical.
I would prefer Keyline to put out an application note on this, but they have yet to do so. Here is there website, phone & email if you wish to contact them yourself to find out more:
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Has anyone actually contacted any of the chassis manufacturers to ask if their alternators can withstand charging a partially discharged LiFePO4 battery bank? Very few lithium battery users are ever likely to require charging from 10% SoC or less. Most will probably only need to replace a couple of dozen Ah. I'm still of the opinion that all this extra hardware isn't necessary. It reminds me of those infomercial ads for oddly named drugs, that basically are trying to sell a solution to a problem that isn't a huge or widespread problem in the real world. Most of the dire warnings seem to be coming from Victron, or other websites and users that seem to like Victron hardware. I'm not saying their stuff isn't good, but they do "have a dog in the fight".
I put 4000 miles on my drop in (2X100Ah) 200Ah Relions last February, and everything is still intact and functionng as designed as far as I know, both the 220A MB alternator, and the Relions.
This blog is sort of what I mean.... no significant comments about the horrors of destroying your alternator by charging your batteries with it. 2017 Sprinter specific. https://windinmyface.com/Sprinter-Al...r-Primary.html
It is pretty easy to tell if the load on the alternator is high and if it is overheating. After I install the Li batteries and before I do any thing else , I will measure the charging amps from the alternator with the Li batteries mostly discharged and I will measure the alternator case temp. If the temp is ok, 200 or less, then I won’t do anything more. I hope that is the case.
Alternators have performance curves, this is an example of the performance curve for the 240 amp alternator that Ford currently uses on the F53 and F59.
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Randy - Manhattan, Kansas
2015 Vista 27N
2020 Ford Escape Hybrid
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Quote:
Originally Posted by powercat_ras
Alternators have performance curves, this is an example of the performance curve for the 240 amp alternator that Ford currently uses on the F53 and F59.
Is there a question or answer here? Or, does this fall into the category mentioned in the blog that I linked?
Let me expand on my concerns about an alternator overheating (particularly at idle speed) if charging a somewhat depleted 200+ Ah lithium battery installation on an RV. This video link from Victron illustrates the problem:
They evaluated two alternators, one a heavy duty standard alternator and the other a Balmar high output alternator with a temperature probe and load management software. The standard alternator operated fine at 80 amps load and at 3,000 rpm but when run at 1,500 rpm it overheated and smoked the windings.
The Balmar alternator with its temperature moderating sensor operated fine at 3,000 and 2,000 rpm keeping the internal temp (how they measured that is a puzzle) at about 50 deg C or 150 deg F.
In my experience operating a Balmar alternator with the temperature sensor on a boat, it cuts back amperage in half when the case temp reaches 180 deg F. The internal winding temp is much higher.
So from the above it seems that most standard alternators will overheat when operated at idle rpms while heavily charging a lithium battery near 80 amps. That is why I think a DC to DC current limiting device may be necessary.
FWIW and I haven't seen any thing directly from Mercedes, but some have reported that Mercedes specifies no more than a 40 amp external, ie not chassis related, load on the alternator. Others have reported that 60 amps is ok. That would seem to be roughly consistent with the Victron test above.
Location: Sarnialabad, Peoples Republik of Canuckistan
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I've seen that video before, and I always wondered why they removed/disabled the BMS? To ensure the amperage draw would be maxxed out/excessive and not mitigated by a functional BMS, which most top end lithium batteries come with?
Do your due diligence and do what works for you.
I'm just using personal anecdotal evidence that suggests that it's not that big a problem for me, using my system of 200Ah lithium, with a 220A MB alternator, as an example. I might look further into it if I wanted to install another 200Ah of capacity, but that's speculative, and unlikely to happen any time soon. I also have other charging options that may mitigate the wear and tear the lithium draw places on my alternator, but that's also just speculation.
It will be intetresting to see what you finally choose to do.
I will definitely run some tests and measure the alternator case temps with no current limiting device before I install one. I will let you guys know how it works.
You could do the same test by shooting your alternator case with an IR gun while idling with a discharged Li battery. If it stays below 200 F you are probably ok.
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When the weather improves, I'll give it a try. Wish the border was open, so that I could find an IR therometer gun for less than a mortgage payment. Any recommendations on IR temp guns? I see a bunch at Granger.ca. I'll have a look there.
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Wish I could get over to HF, border still closed. Grainger up here, is an order, and wait 2 weeks for it to ship to the closest store. Amazon.ca is full of ridiculously inflated prices, and not every seller on Amazon.com ships to Canada. I'll keep looking, and see if I can find something decent for less than C$100. It's ridiculous how we get gouged up here for identical products sourced south of the border.
For fun, I tried buying it, because Amazon says "we're showing you things that ship to Canada". As soon as I tried to check out with it, got the "sorry this item can't be shipped to your address".
I'll see if someone has one on .ca - thanks for the suggestion.
I have been following several topics (posts/threads) about all the concern about lithium drawing so many amps that it will destroy the engine alternator.
What I haven't see is folks actually testing their RV to see just how many amps a well discharged lithium battery actually pulls from the alternator.
This afternoon I did a test on my 2006 Journey and 400AH of lithium battery.
I discharged the batteries to about 30% SOC. The batteries, with only about a 3 amp load, were at 13.0V. I started the engine and at idle the voltage at the chassis batteries was 13.9V, measured with a Fluke meter. The amps measured with the Trimetric monitor was at 34amps. The voltage at the house batteries (while charging at 34 amps) was 13.3V.
I'm not surprised with the 0.6 voltage loss from the chassis batteries to the house batteries.
In my Journey (36' long) there is about 80-90 feet of cable from the alternator to the batteries. The alternator is at the very rear, the solenoid is all the way at the front and I installed the batteries in a cabinet in the bedroom. There is about 10'-12' of extra cable from where the house batteries were originally installed (right next to the chassis batteries) to where they are now. The inverter/charger & solar controller are also installed in the cabinet with the batteries.
I didn't spend much time testing, I only idled the engine for about 10 minutes and the amps stayed at about 32-34 amps.
I can't see where the 30 or so amps will damage the alternator.
Every type and model RV will have different results. A lot will depend on the wire size and length from the alternator to the batteries.
80-90' is a huge distance for the alternator charging cable. Is that both ways, pos and neg? Must be. What size wire?
FWIW if it is #2 wire and the 80-90' distance is both ways, that will result in about a 0.5 V drop at 34 amps which is pretty close to the 0.6 V you measured.
In a Class C where the batteries are below the steps the total two way distance can't be much more than 15'.
80-90' is a huge distance for the alternator charging cable. Is that both ways, pos and neg? Must be. What size wire?
FWIW if it is #2 wire and the 80-90' distance is both ways, that will result in about a 0.5 V drop at 34 amps which is pretty close to the 0.6 V you measured.
In a Class C where the batteries are below the steps the total two way distance can't be much more than 15'.
David
I'm not sure of the wire size. It is the wire installed by the Mfg. I think the long run may be 1/0 as that is what is attached to the solenoid. I think the wire from the original battery to the current location is #2. The only wire I installed was about 4' of #2 from the old inverter location to the current battery and inverter location.
In the 4 years of using this system I haven't bothered to charge the batteries from the alternator, 650 watts of solar has worked very well.
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