DIY 280A Lifepo4 Lithium in 2019 Roadtrek

[Winston]

Originally Posted by booster

I converter the 250 to remote regulator when we got the 280 amp version for a second alternator . . .

An interesting alternative for Larry to consider . . . but this raises the question why is the 2nd alternator there? By that we mean, what is it connected to that may be impacted by a change in 2nd alternator operation?

For us the 2nd alternator was added for the sole purpose of charging a stand-alone lithium system. Not sure whether Larry has that flexibility . . .

[markopolo]

14.4V/14.3V would effectively get the battery to 100%. 13.8V can result in a near fully charged LFP battery, maybe 97% or 98%, so that lower voltage regulator looks like a good option. The existing 14.7V is the start of overcharge territory and likely adds unnecessary wear & tear on the cells.

The auxiliary alternator in those RT's is used for battery charging and powering the inverter. The 14.7V or so output was likely selected to charge an AGM battery as fast as possible.

I think that Larry's idea of using multiple BMS units in parallel could work. The design of the board looks ideal for stacking using copper spacers. Voltage, current and temperature can all be calibrated. All 50+ settings can be programed identically. Balancing can be turned off on all but one of the BMS units used in parallel. Component tolerance variation will still make them slightly different but If you have the equipment and skills to do all that then the BMS units should be very closely matched.

JBD 150A V1.5.jpg

There are several revisions of that BMS so you should match version numbers. (v1.7 last time I checked)

These folks https://www.currentconnected.com/lea...chasing-guide/ have this to say about it:

Let’s say however, you decide to add a 2000 watt 12 volt to 120v inverter to your RV to power appliances such as a microwave or coffee pot – This inverter at full load would draw approximately 200 amps on the 12v input. Neither a 50 amp or 150 amp BMS is sufficient. Now, it is required to parallel multiple BMS units for increased current capacity, or select a larger BMS unit. Good engineering practice is to only utilize 75% of the BMS’s continuous current rating when connecting in parallel, to prevent one BMS from cutting out prematurely due to real-world differences in wire resistance and length. In other words, 2 of the 150 amp BMS units connected in parallel should only be considered equivalent to a 225 amp BMS.

It's all worth thinking about & discussing further.

[Davydd]

This I published in my former 2014 ARV Sprinter about second alternators with observable testing in a place, Natchez Trace where I could drive a steady non-stop 50 mph to observe charging. I had the Nations 280 alternator replaced with ARV’s new standard, the Delco Remy 330. They have a video comparing the Nations to the Delco. I don’t know if anyone else has installed Delco second alternators. I have the same alternator in my current van. This is the video.

https://www.youtube.com/watch?v=XANYxoEF_HY

With my former Nations second alternator I reported in the past the amperage output started going down at around 90% SOC. Now I am not sure if heat contributed to that. You charge an overnight stay so fast you really don't know. So I got a chance to test my new Delco Remy 330 on the Natchez Trace where you can drive a constant 50 mph non-stop. It was a heavy overcast day so solar had little contribution. I forced my battery down to 60% SOC or in effect would have to put about 256ah back into the battery (40% of available 640ah). In starting out I could monitor as high as 330 amps output briefly but after a few minutes it settled down to a steady 270 amps reading which means about 280 amps since I am discharging an average of 10 amps with refrigerator and inverter on. At 95% SOC the amperage started to steadily fall as the Balmar was braking the output. 100% SOC was reached in 1 hour 2 minutes. After that the Silverleaf reading (Advanced RV’s monitor) would be a minus discharge amperage number alternating with a small compensating plus amperage number to hold 99% SOC. Both the Nations and the Delco Remy alternators had the Balmar regulator.

[larrylwill]

I was not offended in any way. It seems that there was several different types of 2nd Alternators. To be honest I do not know what I have. I suppose I will pull all the paperwork and maybe I can find something. I know I negotiated with a RV seller to get the best price I could they were in a different state and I was negoating for a 2018 late in the year then I heard the 2019 would be out in March and they said they could get me one for the same price. They were the biggest dealer in their state but did not sell Class B's so I was the first, The didn't know anything about them, So I asked or and got what I asked for. I assembled the 280A battery and bought the biggest BMS I thought I needed, I knew almost nothing about them. I watched and read all I could and all I could find worked the same way mine does. Almost everyone's solution was a DC to DC charger, I resisted with other solutions but each one got critized. Yes your right my Alternator puts out 14.8v but the BMS knocks it down to 14.6. I thought about bypassing the BMS and charging directly and using a diode to knock the voltage down to 14.1v. I posted my questions on 3 groups, first the solar fourm, (Will Prouse) then the Simplicity Roadtrek group on Facebook then this one. I knew there was 2 types of BMS, a 2 terminal one and a 3 terminal one. Is the 2 terminal one they type that passes the full charge current? I could have bought one of those and saved the money of the DC to DC charger.

[markopolo]

They have a continuous current rating. Use a 150A BMS for up to 150A continuous current, use a 200A BMS for up to 200A continuous current etc.

My preference would be to oversize the BMS capacity relative to the expected load so it is not maxed out though.

[larrylwill]

I agree, I would need a 300A BMS, I couldn't find one when I looked and most that I find now have lower input amperage than the BMS output current.

[larrylwill]

I bought a 60A Renogy dc2dc charger. I connected the input to my 280A 2nd alternator, The B- output to my BMS C- which is the load and charge input, the B+ of the Renogy to the B+ of my battery and other circuits. In other words I just inserted it between the Alternator output and BMS. I then connected the D+ to the starter battery. I started the RV and I get nothing. I have 12v on the D+ and nothing on the alternator output. I also tried a 2nd 10A 12v Battery just or the D+ lead. No leds light. I took it out and hooked the alternator back up to the BMS and the alternator works. I would think that the green led should light when it sees 12v, it does not. Please Help.

[markopolo]

That Renogy unit is a B2B type, "Battery to Battery", so it's placed between two batteries. Also, a common chassis ground is used.

DCC1212-204060-Manual pdf.png

[woodbri]

The UHG and Balmar have two fuses, check them. On my 2016 Roadtrek they are in the wiring harness. I have to climb under the front of my van to get to them.

[larrylwill]

I don't have a Balmar and everything works without it in the circuit. The green led does not come on when I connect the D+ and it is supposed to according to the instructions.

With a BMS on the battery effectively it is connected exactly like your diagram.

[booster]

Originally Posted by larrylwill

I don't have a Balmar and everything works without it in the circuit. The green led does not come on when I connect the D+ and it is supposed to according to the instructions.

With a BMS on the battery effectively it is connected exactly like your diagram.

Not exactly the same, I think, because the diagram shows a single alternator system and you have two separate ones. You are connected to an alternator that is not connected to that battery on the input side. Normally, modern products check to see if there is a viable battery with voltage and capacity on the input from the alternator, and you do not have that. The voltage reference is different.


There is also the possibility that the alternator would have started as it has an internal regulator and if so it could have gone to very high voltage and blown the alternator diodes and/or the B to B. Hopefully the internal regulator also looked for a battery before starting.

[markopolo]

Connecting the alternator to the DC-DC input causes the alternator to not see a reference voltage because the Renogy DC-DC input and output terminals are isolated.

This note was in the previous Renogy manuals:

Important Note: The Alternator will not be connected directly to the input of the DC-DC. The alternator must be integrated with the starter battery and this circuit is connected to the input starter source terminals on the DC-DC.

You could always check with the alternator manufacturer to find out if their alternator can run without being directly connected to a battery. I suspect they'll tell you it needs that direct connection to a battery.

[GallenH]

Interesting discussion. So my old 97 PleasureWay is stock. I don't honestly know if I have a separator or an isolator in the circuit (anyone know?).

But I've always been confused about how these are wired. Originally I thought that the alternator provided power to both the chassis and the house batteries splitting off to send the alternator output to both simultaneously. The function of the separator/isolator being to prevent the house battery from drawing on the chassis battery.

But now I see diagrams where the house battery is really being charged through the chassis battery. So I remain confused. Could someone do a "101" explanation of how this works.

Open to PM if it's felt that this is too far afield from the OP.

ThxVeryMuch.Glenn

[booster]

Originally Posted by GallenH

Interesting discussion. So my old 97 PleasureWay is stock. I don't honestly know if I have a separator or an isolator in the circuit (anyone know?).

But I've always been confused about how these are wired. Originally I thought that the alternator provided power to both the chassis and the house batteries splitting off to send the alternator output to both simultaneously. The function of the separator/isolator being to prevent the house battery from drawing on the chassis battery.

But now I see diagrams where the house battery is really being charged through the chassis battery. So I remain confused. Could someone do a "101" explanation of how this works.

Open to PM if it's felt that this is too far afield from the OP.

ThxVeryMuch.Glenn

What you describe is the normal setup with one alternator. Most second alternators are setup to only charge the coach batteries and leave the original alternator to just charge the starting battery. B to B chargers are often used to get the right charge profile and limit current to the coach batteries. That can also be done by using a programmable regulator on the coach battery alternator.

[markopolo]

Originally Posted by GallenH

............................. Originally I thought that the alternator provided power to both the chassis and the house batteries splitting off to send the alternator output to both simultaneously. The function of the separator/isolator being to prevent the house battery from drawing on the chassis battery......................

Your PW likely has an isolator (diode based isolator). Your understanding is correct when/if using an isolator. They're single input to multiple outputs. Input to Output is not isolated in the forward direction but Output to Input (reverse direction) is isolated. Output to Output is also isolated.

Separators (solenoids/relays etc.) function similar to a switch. Power flows forward or reverse when the solenoid is closed. Power doesn't flow when the solenoid is open.

On the DC-DC unit being discussed, Input and Output are isolated. Power doesn't flow through in the reverse direction. In the forward direction, power is received then modified and then sent to the output. It's Boost/Buck not pass-through. The output voltage can be higher or lower than the input voltage depending on the settings.

[GallenH]

A couple of questions (statements):

1. So in my RV the alternator goes to the isolator which passes it through to both the chassis and the house batteries. What's reaching my house battery is simply a straight voltage, or at least, not one which is going to give me multi-stage battery charging. That's where the DC-DC charger comes in. It could be placed after the isolator with no issues?

2. I think that I misread the diagram from MP. The positive on the chassis battery seems to be a common point. Nothing's going through the chassis battery, right? And when the ignition is off, the DC-DC is off so the house battery isn't draining the chassis battery. Am I close?

[larrylwill]

Originally Posted by booster

Not exactly the same, I think, because the diagram shows a single alternator system and you have two separate ones. You are connected to an alternator that is not connected to that battery on the input side. Normally, modern products check to see if there is a viable battery with voltage and capacity on the input from the alternator, and you do not have that. The voltage reference is different.


There is also the possibility that the alternator would have started as it has an internal regulator and if so it could have gone to very high voltage and blown the alternator diodes and/or the B to B. Hopefully the internal regulator also looked for a battery before starting.

the alternator works just fine. Also the BMS reads 13.5v where the dc2dc is connected. Besides I tried connected directly to the battery. I have a AHM I could connect to the input. As soon as I recover from my sholder operation I will try.

[booster]

Originally Posted by larrylwill

the alternator works just fine. Also the BMS reads 13.5v where the dc2dc is connected. Besides I tried connected directly to the battery. I have a AHM I could connect to the input. As soon as I recover from my sholder operation I will try.

The point is that you need a battery on each side of the B to B. One on the input side with alternator and one on the BMS side. I can't be done with just one battery on the BMS side and none on the other AFAIK and Renogy manual states plainly.

[larrylwill]

I will hook up the AGM

[markopolo]

Originally Posted by GallenH

A couple of questions (statements):

1. So in my RV the alternator goes to the isolator which passes it through to both the chassis and the house batteries. What's reaching my house battery is simply a straight voltage, or at least, not one which is going to give me multi-stage battery charging. That's where the DC-DC charger comes in. It could be placed after the isolator with no issues?

2. I think that I misread the diagram from MP. The positive on the chassis battery seems to be a common point. Nothing's going through the chassis battery, right? And when the ignition is off, the DC-DC is off so the house battery isn't draining the chassis battery. Am I close?

It would be better to not use the isolator when switching to a DC-DC unit. Alternately, it could remain in place but be bypassed by moving the chassis & house lugs to the alternator terminal on the isolator. There might be other wires that you need to know what they do. GM vans from that period had a voltage sense wire for example. A voltage sense wire would have to be moved also as it makes the alternator to compensate for the isolator caused voltage drop.

A DC-DC unit will draw from the chassis battery when/if the alternator can't keep up with load when hot and at idle for example. Some units have voltage triggers that should avoid that. Voltage sensing can be added to a Renogy -> https://www.classbforum.com/forums/f...way-11572.html