Chassis Battery *versus* Home Battery ? Must start an Onan Gen.

[rickst29]

I will soon be upgrading a friend's Class B (a Leisure Travel "Free Flight", vintage 2011. Replacing AGM with Lithium for the living "coach area". Parts:

1. A single BattleBorn 100Ah battery;
2. A Progressive Dynamics "Wildkat" replacement Converter board;
3. A new Solar Controller Epever 'BN" series) and probably
4. a coulomb counter meter.

A Leisure Travel diagram shows the whole system wired together, with both batteries on the left side if this diagram. (Image attached). I do not have the subsequent page, which probably describes some of the numbered labels in detail. But it appears that BOTH batteries are on the same bus, with a battery isolator I don't trust between them.

I plan to separate the Chevy 12V battery (and truck equipment) from the "House 12V", and interconnect them with only an ignition switched Renogy DC -->DC charger box. Programmed for lithium, of course.

That's a one-way box, which will only take up about 20A (270 watts) from the running engine to charge the new "House" Lithium. It does not allow power to run backwards, so the new Lithium house battery can no longer "help" the "Chevy" side of things. And in the reverse direction, the Lithium can only provide about 200A to start the Onan Generator, unassisted from the "chevy" battery and alternator. Even running the Chevy, it can only get 20A through the Renogy.

Do you all have any ideas or recommendations about this? I own a Travel trailer with a variation of this set up, but if class B "House" batteries need to be involved in the main chassis - let me know. On the right side portion of the wiring diagram, (which I didn't attach), the lower section does list a modification to add the connection between the batteries - and this particular RV might not even have it yet.

[rickst29]

Because she thinks that the used RV was built in 2010, it might not ha e this wire. The addition of the inter-linking wire "Battery Boost Wire" was done from September 2011. That's update is noted in the bottom table of 'revisions'.

[booster]

With any RV electrical systems changes, IMO, you always should confirm all the wiring either matches the wiring diagrams or doesn't as it very common for them to be wired differently from the factory or have had changes done on used ones.


As for the generator starting, it should start easily off a 100ah lithium battery, and even if it doesn't the engine can be started to give 20 amp and higher voltage kick to the starting.


Be aware that the B to B and maybe some of the other components may not activate if the the lithium battery is in shut down mode for some reason or other as they may need a battery reference in the circuit to initialize. This will make it impossible to start the generator as there is no battery seen and the B to B won't come on to connect to the engine.

[markopolo]

Booster makes a great point about checking to see if the Renogy unit needs to see a battery in order to work. You could end up with a coach with no house 12V and no way to easily get the lithium battery back online.

The ability to boost the chassis battery from the coach batteries and the ability to maintain the chassis battery when the coach is plugged in or on solar are both really nice to have.

Chevy vans do have some parasitic loss at the chassis battery so the system you design needs to take into account how often the van is driven.

BIRD is noted on the diagram and typically BIRD is a Bi-directional Isolator Relay Delay. I had a Triple E Coach with a BIRD and that allowed the chassis battery to be maintained by the coach battery charge sources including the solar panel. It used a Solenoid (also note on the diagram) which probably wasted 12W or so.

The Battle Born battery's voltage would be high enough to trigger the BIRD to join the coach and chassis batteries and, by doing so, eventually draw the Battle Born battery down to a very low SOC as the BIRD break point is typically 12.8V to 12.6V.

Two advantages of LiFePO4 are fast charging and high current output. The planned upgrade doesn't appear take advantage of either characteristic so it would help to know what reasons are behind the decision to upgrade. I ask because it's very possible that $1,500 or so spent might not result in any significant gain that couldn't be realized by learning how to better care for the lead acid battery.

My understanding of the PD lithium units is that they have a continuous 14.6V output. I wouldn't choose that method for lithium batteries that I own.

[rickst29]

Originally Posted by markopolo

Booster makes a great point about checking to see if the Renogy unit needs to see a battery in order to work. You could end up with a coach with no house 12V and no way to easily get the lithium battery back online.

Yes, if I remove the BIRD (strikethrough, because I'll be running it the Renogy backwarsds, as a reaplcement for the BIRD), then I need to assure that it is switched by the Chevy ignition, only sucking power when the engine is on... (NO, the D+ engine-on detect will be attached to the Lithium battery - the power source in this case. See below https://www.classbforum.com/forums/f...tml#post113378. ) The ability to boost the chassis battery from the coach batteries and the ability to maintain the chassis battery when the coach is plugged in or on solar are both really nice to have, and I lose them if I remove the BIRD. My worry with the BIRD is only this: when will it stop sucking from Lithium, in charging the lower voltage "Chevy" batterye?

Originally Posted by markopolo

Chevy vans do have some parasitic loss at the chassis battery so the system you design needs to take into account how often the van is driven.

BIRD is noted on the diagram and typically BIRD is a Bi-directional Isolator Relay Delay. I had a Triple E Coach with a BIRD and that allowed the chassis battery to be maintained by the coach battery charge sources including the solar panel. It used a Solenoid (also note on the diagram) which probably wasted 12W or so.

The Battle Born battery's voltage would be high enough to trigger the BIRD to join the coach and chassis batteries and, by doing so, eventually draw the Battle Born battery down to a very low SOC as the BIRD break point is typically 12.8V to 12.6V.

Parasitic loads can be handled - I'll have her using the RV for occasional grocery runs if I take out the BIRD. That was my worry about the BIRD - The fully charged LFP will pretty quickly drag down from 13.6v to 12.8v. From there, if the BIRD allows further droppage to 12.6V, or even worse, then the Lithium has become pulled down to a very low SOC.

Two advantages of LiFePO4 are fast charging and high current output. The planned upgrade doesn't appear take advantage of either characteristic so it would help to know what reasons are behind the decision to upgrade. I ask because it's very possible that $1,500 or so spent might not result in any significant gain that couldn't be realized by learning how to better care for the lead acid battery.

Originally Posted by markopolo

My understanding of the PD lithium units is that they have a continuous 14.6V output. I wouldn't choose that method for lithium batteries that I own.

They do that, and it's a slightly higher charging voltage than BB recommends. They quit when current becomes close to zero, and then restart in full (at 14.6V "bulk mode"), based on somey "ready for recharging" Voltage which I don't know. I own one with my Lithiums, and the resulting range of SOC (from the Coulomb Counter) seems to be pretty well managed, though maybe a tiny bit on the "overcharging" side of optimal for storage. A really simple and stupid algorithm, but it works pretty well. (PD is always changing things, and could be switching to something a bit different at almost any time.) You have the superior Victron, I assume?

The key reasons for this upgrade path were: #1 No SPACE to add a second LA battery into the battery area; #2 higher current capability for starting the Onan generator; #3 ability to pull more energy from the battery between recharge opportunities (pulling down to 20% SOC, instead of 50% SOC on the older AGM); and #4 some likely savings in the extreme long term. But also:
- - -
#5: It sounds sexy, and she wants to impress people. I was pretty much told to switch into a Lithium configuration, even though the Chassis battery becomes more problem-prone by removing the BIRD.

Maybe I should leave it in place, and only remove after testing battery Voltages after it has a long rest on the driveway? One of those might be coming up, after her next trip. There might be one, up to about 3 weeks. If LiFePO4 isn't dragged much below 12.7V, I could leave it in there. AND bring a jumper cable with me, if it went

[rickst29]

while the Converter is plugged into shore power, the converter will generate full power (about 14.6V) until the current falls to a very low level. I think that will cook the "Chevy" battery to death.

[hbn7hj]

Quote:
Originally Posted by markopolo View Post
My understanding of the PD lithium units is that they have a continuous 14.6V output. I wouldn't choose that method for lithium batteries that I own.

I have several of them. While charging the voltage displayed on the battery monitor slowly climbs to 14.6 volts when fully charged then the charger turns off. An older version of the same model does not turn off.

[rickst29]

Originally Posted by hbn7hj

Quote:
Originally Posted by markopolo View Post
My understanding of the PD lithium units is that they have a continuous 14.6V output. I wouldn't choose that method for lithium batteries that I own.

I have several of them. While charging the voltage displayed on the battery monitor slowly climbs to 14.6 volts when fully charged then the charger turns off. An older version of the same model does not turn off.

My version is an aftermarket mod called the "Wildkat". I have one in my own Trailer, which I tested with an LFP battery and variable small loads on a test floor (my tiled living room ) before installation. It continues working past Voltage reaching 14.6V, until charging current also falls off. (There was perhaps 10 minutes of "bulk mode" CV charging before it quit, with most of the time still > 40A.) I bought a second one for this Van Conversion. It's replacing the Converter section of an old Parallax. They were kinda in ALL configurations, and never even heard of Lithium batteries.

I don't own (and have never tested) an unadulterated original PD Lithium model. It would be very unfortunate if they quit before reaching near-zero current, because that would leave at least 15Ah, maybe as much as 30Ah, un-used in my pair of LFP batteries. "Wildkat" and my Solar are perhaps guilty of the opposite extreme, keeping them near near 100% all the time. (But my Trailer stores in my garage, with disconnected phantom loads and the 30A cord left unplugged until just before trips. The battery slips down only a tiny bit, with nothing but the battery monitor connected.)

With that said, let's focus on my Class-B upgrade, and leave my "Trailer" experience off the table (although it's been wonderful, all the time.)

[markopolo]

Thanks for the info Harry - I've seen several posts on other forums that say the PD lithium chargers stay at 14.6V when on and folks either unplug or switch the AC breaker for the charger off. Good to know the newer units stop outputting 14.6V on their own.


-------------------------------


If 30Ah or more capacity is the goal the adding 100W of solar should cover that. AGM's can be taken down to 20% SOC and if done regularly then they will have to be replaced more often. If the van has an absorption fridge and solar then it's difficult to see how or why the battery would be regularly taken so low.

I do understand wanting lithium batteries though

An Amp-L-Start Revision G2 version or better could replace the BIRD for keeping the chassis topped up from solar.

The Solenoid could possibly be repurposed using momentary switch to help bring the lithium battery back online if ever needed

[rickst29]

And so, here is my idea:

Run the Renogy DC-->DC battery charger backwards. The charging profile will be SLA (or maybe AGM, if that's what she now has up front), and the source will be slightly-higher-voltage Lithium "house" bus. I'll remove the BIRD, and use the Renogy to charge the "chassis" battery from the higher-voltage Lithium "house" section.

In longer term storage, it gets charged 30A-plug --> Wildkat Converter --> "House-12v bus" --> Renogy charger --> Chevy (SLA or AGM) battery.

This way, her Lithium can be maintained with high voltage (14.6V) from the Converter, while plugged in between trips at home, while the "Chassis" battery bus is is charged by the plugin at lower voltage (14.2V GEL max, or 14.4 AGM max, or whatever) - whenever it needs, because I'll have the Renogy "is the alterator on?" wire plugged into the House/Lithium 12V bus.

I want to separate these electrical systems, except for the Renogy DC->DC Charger.

[rickst29]

<SNIP>....

Originally Posted by markopolo

.... An Amp-L-Start Revision G2 version or better could replace the BIRD for keeping the chassis topped up from solar.
The Solenoid could possibly be repurposed using momentary switch to help bring the lithium battery back online if ever needed

</SNIP>
That would have been excellent I wish I had 'd found your suggestion earlier. Instead I have the Renogy DC->DC already coming, while this machine does exactly what I needed - for $35 less. (Maybe 'prime shipping' makes up for some of that difference. Or maybe not... ).

[markopolo]

Your friends excitement of getting a lithium battery would quickly wear off if you take away the ability to charge the lithium by driving or idling.

You might be able to add a switch on the dash that enables/disables the BIRD as needed. Use the DC to DC charger as you originally planned.

[rickst29]

But she's also got Solar, and an Onboard Generator to handle the fridge while driving.

Originally Posted by markopolo

Your friends excitement of getting a lithium battery would quickly wear off if you take away the ability to charge the lithium by driving or idling.

You might be able to add a switch on the dash that enables/disables the BIRD as needed. Use the DC to DC charger as you originally planned.

I can definitely do that. Or maybe - I can set up a pair of high-current Relays, which swap the I/O leads on the Renogy charger:

master switch (4-pin, closed by ignition "on") drives two other 5-pin Relays. High current with 12V coils, to "flip" the input and output leads (using 2 "secondary" 5-pin Relay).


Relay #1, Renogy "input" is the Common. The coil chooses between two output legs - the "NC" position is the House battery, "Solar +Lithium + 30A plug" on a branch, the connected position (coil has been powered up by the ignition switch) moves the "input" connection over the the Chassis "Engine/Chevy" battery, keeping the Chassis battery charged when it isn't driven often enough (but is plugged in, sitting at home)'.

Relay #2, Renogy "output" is the Common. The coil chooses the "House" versus "Chassis" legs backwards from Relay #1. The 'NC' branch goes out to the Chassis lead. When the engine is running the pulled in, 'Connected' branch swaps over treat the Lithium House battery as "output.
- - - - -
Each wire ("house" and "chassis") is branched to BOTH Relays.When the engine is off, the path goes plug-in --> Converter --> "House" 12v and Lithium --> Relay #1 (connected) --> Renogy Input Input --> Renogy Output --> Relay #2 (connected) #2"Chassis 12v and battery". The Lithium side charges the Engine side.

Now we flip both Relays by running the engine and (maybe) going for a drive. At Relay #1, the Relay Common is taken off from the "House" Connection and moved over, connecting the "Chassis" instead. And, at Relay #2, the output leg is disconnected from "engine/chassis", and connected to "house" instead. The Engine side is now charging the Lithium side.

- - - -
I'm not good with pictures, but I have something like that under the hood of my Trailer's TV. In the case of my 4runner and my own TT, the 4-pin switch is not automatic, but rather becomes "closed" by a dashboard switch. Inputs and outputs are being swapped in the TV with final output to the TT, at Voltage either ~13.5v (not boosted, for towing all other Trailers) or 36V (13.5V input moved to go through a Boost Converter, before reaching Bargman cable and my own Trailer.)

Within my, a detector Relay (not need in the Class-B) sees that Voltage is really high, disconnects the Solar panels from the MPPT - and puts the high-voltage bargeman "battery charge" into the Solar Controller, instead of the 12v load center. The engine charges the Trailer, through the MPPT. It's been working for many years. (I basically run my TT "Solar system" at night, with the TV acting as a giant 450 watt Solar Panel).

This one is less complicated, because damaging high voltage isn't present anywhere. In worst case (failed Relay), one side is left charging itself for a while. But the Renogy controller will need to be set for the lower Voltage battery in the chassis, and might not do all that much for the Lithium.

[rowiebowie]

The above sounds overly complicated to me. I installed 2 x 100Ah Renogy lithium batteries, Renogy 40A DC to DC charger, Renogy 3000W Inverter/Charger, and Renogy SOC Battery Monitor. I basically just took wires from the OEM battery isolator & old Tripplite Inverter/Charger and ran them to new Renogy products.

The only thing I lost is the ability to charge my engine battery while plugged in or running the generator, but of course it still charges while driving. As I have only nominal Solar (and agree with Davydd that solar is not essential with quick charging lithiums), my solution was to wire the solar to maintain the engine battery.

Here is my crude wiring diagram:

[rickst29]

Thank you , great post.

Originally Posted by rowiebowie

The above sounds overly complicated to me.

There's a ton of words in my explanation, but it's only 3 Relays. (And they're very reliable these days). If I have an ignition-switched lead in the wiring compartment, then my way is easy - but if I don't, then your advice is super - use the Solar to maintain the Chassis side, instead of providing mostly-unneeded boost on the Lithium/Coach side.

[rickst29]

Originally Posted by rowiebowie

The only thing I lost is the ability to charge my engine battery while plugged in or running the generator, but of course it still charges while driving.... my solution was to wire the solar to maintain the engine battery.
Here is my crude wiring diagram:

The problem for this RV will be the engine battery in winter. I just took a second look, and it maybe can't be kept 'good' by Solar alone, because her driveway parking spot has the sun blocked in most of wintertime (by the 2-story house, when the angle of sunlight is very low). And so - if I had to choose one direction for the Renogy, it would be backwards. But my scheme of leaving it active all the time, usually backwards -- charging the engine battery, is good (although expensive in comparison to a less complex charger.) The ability to use it forwards, via the Relays, is just a clever bonus.

I could have done the job cheaper with an Amp-L, because I'm bypassing the ignition switch feature on the Renogy. I'm converting the BIRD "engine ignition sense wire" in the compartment to do a different job, while leaving the Renogy lead "hot" in the coach, along with the plugged-in RV Power Converter.) I'll be using short segments of #10 into the Relays, and keeping the big BIRD and main battery post wire segments for as long as I can. Even #10 is tough to connect into high-end ceramic relay sockets. (I might even have to downgrade to #12, for a few inches - but this Renogy will only be the "20A" model, that would be legal for even NEC wiring, and perfectly OK for Chassis wiring.)

(BTW, I'm not sure why you used #4 wire for some of those leads, but I'll admit that bigger is always better, wiring hassles and costs notwithstanding )

[rowiebowie]

Originally Posted by rickst29

(BTW, I'm not sure why you used #4 wire for some of those leads, but I'll admit that bigger is always better, wiring hassles and costs notwithstanding )

And I used 4/0 cables to parallel the batteries and connect them to the inverter/charger. Overkill for sure.

I actually bought 2 more batteries thinking I might go to 4 total. But realizing 4 would't give me meaningful ac run time, take up some of my rear storage space, and not to mention take more time to charge, I did not install them.

Instead, I made a duplicate set up of van components on a rolling cart as a backup power source for my home. They will run the home fridge for 12 - 14 hours and allow me run my van or home generator only 3-4 hours a day to keep the batteries charged. Less noise, fuss, and gasoline compared to running a genny 24 hrs. a day. Already used the system twice in limited power outages.

In the end, I further justified the duplicate system as backup components should any part of my van go down. Only the smaller foot print Renogy batteries fit where I had room to put them inside, and only the Renogy Inverter/Charger fit in the space I had available for it as well. If they ever discontinue production (Renogy changes product fairly often), I have one of each just in case.

[markopolo]

Originally Posted by rickst29

..................... a detector Relay (not need in the Class-B) sees that Voltage is really high, disconnects the Solar panels ....................

Rick - if you get a chance, would you describe your detector relay setup in more detail for me?

Also, do you use blocking diodes with your boost converter or does using the solar controller eliminate any chance of backflow?

[rickst29]

Originally Posted by markopolo

Rick - if you get a chance, would you describe your detector relay setup in more detail for me?

Also, do you use blocking diodes with your boost converter or does using the solar controller eliminate any chance of backflow?

For better or worse, this post is just as long and complex as my previous one . But when you draw it, you will see that there are no concerns with backflow, because the panels and boost converter are never connected to each other. (And also, a half-decent Solar Controller will never allow power to "leak backwards" from batteries into lower voltage "Solar Panels".)

What I described is a slight re-design from a "Travel-Trailer" implementation which I, and a few online friends, have implemented within our Tow Vehicles and Travel Trailers. Within a Class-B, it *does* require the detector relay (adjacent to the Solar Controller). I mis-spoke in an earlier post.

From the front (engine/alternator area) to the "House Batteries" in the rear or side of a Class-B, there is a dedicated "+12v" charging wire for the house batteries, from up front, which interconnects the batteries (usually through a battery protector or BIRD device). This is analogous to the "Trailer Battery Charge" wire and Bargman connecting cord of in my own Travel Trailer. In this scheme, you would eliminate the BIRD/Battery Protect, replacing it with a 12 --> 36v "Booster" under the control of a switch (I have a dashboard switch for that, which is only powered up and capable of switching when the ignition is on.)
- - - -
Now for your question: Out "Back", in the one-relay version, a 5-pin Relay with a 24V coil is configured to feed the Solar Controller "Solar Panel +" input lead as follows:

Pin 30 (normally the high power "input feed") connects to the Solar INPUT of the MPPT controller. Pin 85 (coil "ground") is Chassis ground, identical to "battery -" and also "Solar -" in a negative ground Solar Controller used within a class-B RV with negative grounding.

Pin 87a - the power pin which is connected while the the coil is NOT active (AKA the "N.C.") pin is connected to the "Solar Panel Output +" Solar wire. Meanwhile, Pin 87 - the "Normally Open" power pin which becomes active when the coil pulls in the switching arm from pin 30 - Is connected to that 36v Booster wire. But before connecting that pin, the wire is split, creating another small lead which drives pin 86 (the coil "+" input) with the same Voltage which is present on the 12v-or-36v wire from up front.

When the dashboard switch is not active, the Solar Panels are connected to the Solar Controller - and the "+12v power wire" is connected to nothing at all, because the coil has been presented with insufficient voltage to pull it closed.
- - - -
The one-relay version, although more simple to wire up, leaves no connection at all from the "chassis" 12v to the "house" 12v. (With Lithium batteries in the "house", you normally DO want it running that way). But if the batteries are identical Lead-Acid types, you might want to keep the BIRD present - and use it by adding another Relay.

In the two-Relay version, another 24v coil Relay comes first. But it is run forwards: 12v or 36v comes in on pin 30 "common power input lead", (still with a small lead to drive the coil on pin 86). Pin 87A goes to the BIRD. Pin 87 becomes input to the Pin 87 on the second Relay and also provides coil power on pin 86.
- - - -
When I ran a two-relay version, I actually used a "normal" 12v-coil as the second Relay, pulling the Relay "+" Pin 86 from a small second lead, attached on the "12v output" line (into the BIRD) from pin 87A of the first Relay. It only contains Voltage (12v) during the case that the first Relay has selected the BIRD. But the power inputs were swapped - genuine Solar Input when the coil was ACTIVE ("Solar +" into pin 87A, and power from Relay #1 into pin 87 (now the INACTIVE COIL "input" port).
- - - -
I found good availability for 24 volt coils and 36 volt boosters. The limiting factor in a booster configuration like this MUST !!! be the Solar Controller. If you have an extremely high-powered Solar controller trying to pull too much power and current from a less capable under-the-hood voltage booster, the booster will release its magic blue smoke. (You don't want that smell to be released.) In implementations which I have designed, we limit the Solar Controller input current so that it draws no more than 80% of the rated output power on the Voltage Booster.

I might soon be implementing this in another friend's Class-B, along with a new Solar upgrade.

[rickst29]

Originally Posted by rickst29

while the Converter is plugged into shore power, the converter will generate full power (about 14.6V) until the current falls to a very low level. I think that will cook the "Chevy" battery to death.

The Power Converter and Solar Controller are now connected to only the Lithium house batteries. For the case of a heavily discharged Chevy "Chassis" we now have an emergency interconnect switch (capable of extremely high current), just for the purpose of starting the Chassis Engine or Generator when the Chassis battery has gone dead. The Onan "Engine Start" is otherwise dedicated to the chassis battery.

I expect that the "emergency interconnect switch" will be used several times per year, and so I located it in the lower hallway of the coach - labeled and readily accessed for use. The panel was originally equipped with a couple of other electrical devices, and also had room for the upgraded Solar Controller.