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Old 09-24-2020, 09:45 AM   #1
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Lithium Ion (LiFePO4) Upgrade on 2007 Seabreeze

Those of you who are planning to upgrade your late model National RV motorhome batteries from lead acid to lithium ion, it is not a straight forward process. I don’t have a wide range of experience with motorhome battery management systems, but after upgrading my 2007 National RV Seabreeze to LiFePO4 house batteries while leaving the flooded lead acid chassis battery, I know quite a bit about that battery management system and I’ll share that here.

The National RV system (manufactured by RV Custom Products) uses an interconnect solenoid to connect the house and chassis batteries under the following circumstances:

• When on shore or generator power and the house batteries are fully charged, the house and chassis batteries are connected by the solenoid so that the chassis battery can be charged by the inverter/charger (or converter).

• When driving and the chassis battery is fully charged, the house and chassis batteries are connected by the solenoid so that the house batteries can be charged by the alternator.

• When off grid and the chassis battery is too depleted to crank the engine or generator, the house and chassis batteries can be connected by the solenoid by pressing the “emergency start” button on the dashboard. The RV Custom Products controller activates the Solenoid for one minute. Other MHs that I have owned require you to hold the switch while starting.

I only replaced my house batteries with lithium and left the chassis batteries as lead acid. Since lead acid and lithium ion batteries have vastly different charging requirements, using the solenoid to facilitate charging the house batteries from the alternator and the chassis batteries from the inverter/charger will not work; however, the solenoid is required for the emergency start and we don’t want to lose the that function. If one was to upgrade both the house and chassis batteries to lithium, the solenoid could still be used for charging as long as the alternator is protected by a DC-DC charger (see below).

With the inverter/charger configured for lithium (AGM, actually), it cannot be used to charge the flooded lead acid chassis battery. The solution I used for that is to use an inexpensive battery charger powered by the inverter AC input circuit. (Any AC circuit would work but the inverter circuit is available in the Seabreeze compartment that houses the battery control circuitry.) That one was easy.

Lithium batteries will take all of the charging amperage that you can throw at them. Lead acid batteries can only absorb so much. If you hook a lithium battery directly to the alternator driven chassis battery charging system, it will quickly burn up the alternator. In order to charge the lithium batteries from an alternator, a DC-DC charger is used to control the amperage and charging profile. The input current to the DC-DC charger comes from the chassis battery (which is connected to the alternator) and the output goes to the house batteries. There is an input signal to the DC-DC charger that tells it when to charge. That input is connected to the ignition switch so that it only charges when the ignition is on. (This is not optimal in that if the ignition is turned on but the engine is not started, the charger will draw from the chassis battery without the alternator replenishing it, so you don’t want to have the ignition on without the engine running for very long or it will drain the chassis battery. Some people opt for a dashboard switch to control when the charger is active.) I took the input power for the DC-DC charger as well as the input signal mentioned above from the relay that is on when the ignition is on (J5 on the circuit board) and I fed the charger output to the house batteries through J7 (that the inverter/charger is connected to).

It would be easy to implement the emergency start functionality that requires the dashboard switch to be held while cranking the engine; however, that would involve the dashboard switch and the wiring between the switch and solenoid to carry the current that the solenoid requires to operate. Rather than go that route, I opted to use a small microcontroller to operate a relay which energizes the solenoid. The dashboard switch connects one of the microcontroller inputs to ground drawing virtually no current. When the microcontroller sees the input go to ground, it energizes the relay which in turn energizes the solenoid. It leaves the relay and solenoid energized for one minute, replicating the original behavior. You have to disconnect the activation wire from the solenoid (the yellow wire that comes from the circuit board to the solenoid). It gets replaced by the wire from the relay that is controlled by the microcontroller.

That is what I did to upgrade my Seabreeze. If one wanted to do a trivial implementation where the house batteries are only charged from the inverter/charger and the chassis batteries are only charged from the alternator and there is no emergency start function, just drop the new batteries in, and disconnect the activation wire (the yellow wire) from the solenoid. In any event, you will have to change the settings on the inverter/charger to lithium (or AGM if there is no lithium setting).

I used two of these batteries in parallel for 240AH total capacity. https://smile.amazon.com/Lithium-Pho...0871339&sr=8-5

I used this DC-DC charger. https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I used this AC-DC battery charger: https://smile.amazon.com/Schumacher-...s%2C515&sr=8-7

Here is a link to the RV Custom Products page containing the schematics for the battery management system. The Word document linked to on that page is very helpful. https://rvcustomproducts.com/130325

I used this microcontroller: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

Hooked to this relay: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

Except for the emergency start function, this is totally a DIY friendly project as long as you know a little about 12 volt circuitry (auto electrics). If any of this intimidates you, consider getting professional help. You are welcome to pick my brain here… just post questions in a comment.

As for the emergency start function, if you know anything about Arduino microcontrollers, this is a very easy application. If not, it is easy and fun to learn. (Just Google “Arduino”.)

Hope this is helpful to someone!

-Eric
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Old 09-24-2020, 10:00 AM   #2
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Here are some pictures:

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Before Picture of the battery compartment

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After picture of the battery compartment

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Battery control center compartment with AC-DC charger on the left, microcontroller for emergency start top center and DC-DC charger to the right of the microcontroller.

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Closeup of the microcontroller.
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Old 09-24-2020, 10:07 AM   #3
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I have been studying the conversion from lead-acid AGM batteries in our MH to LFP4. The first thing I did was to look at the inverter/charger, now a Xantrex 458.

I called Xantrex and found that their newer model the Freedom XC, can be set to support charging LFP batteries. The advantage to using this equipment is that it fits into the original design specs for the electrical system in our MH.

JMHO - always take free advise for what its worth
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Old 09-24-2020, 10:59 AM   #4
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There are several different configurations possible when moving to LiFePO4 House batteries. The chassis batteries can be flooded lead acid (FPbA), AGM or LiFePO4. Here are the considerations for each configuration:

FPbA chassis batteries - you cannot use the inverter/charger to charge the chassis batteries when its primary purpose is to charge the LiFePO4 house batteries. If you want to charge your chassis batteries on shore or generator power, you have to use a separate AC-DC charger. Also, the alternator cannot be used directly to charge the LiFePO4 house batteries without damaging the alternator. Use a DC-DC charger to isolate the chassis and house batteries and limit the current draw on the alternator.

AGM chassis batteries - the factory inverter/charger on late model National RV products does not have a lithium charging profile, so AGM is used for charging the LiFePO4 house batteries. It seems likely that one could use the inverter/charger to charge both the house and chassis batteries at the same time, but I would recommend running that past the inverter/charger manufacturer. You will still have the same issues with the alternator charging the LiFePO4 house batteries requiring the DD-DC charger. If you have upgraded your converter/charger to one that uses a lithium profile, you will have to isolate the batteries as with the FPbA case above. If you treat the AGM batteries the same as FPbA, you will be safe.

LiFePO4 chassis batteries - If you upgrade both your house and chassis batteries to LiFePO4, you should be able to leave the battery distribution center as is. The only consideration is that you will have to do something about the alternator charging. The DC-DC chargers that I am familiar with are not supposed to be connected directly to an alternator. There would have to be some other mechanism for limiting the current drawn from the alternator. Sorry, but I don't have the answer for this one, but I'm sure it is out there somewhere.

Hope this helps,
Eric
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Old 09-24-2020, 11:58 AM   #5
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Victron dc-dc chargers connect to the start battery/alternator and to the house battery. They take the voltage normally supplied to the starting batteries and convert it to the proper voltage to charge lithium batteries. They will also limit the current going into the house batteries, so you will not overload your alternator.
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Old 09-24-2020, 03:10 PM   #6
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Quote:
Victron dc-dc chargers connect to the start battery/alternator and to the house battery. They take the voltage normally supplied to the starting batteries and convert it to the proper voltage to charge lithium batteries. They will also limit the current going into the house batteries, so you will not overload your alternator.
That works for AGM or FPbA chassis batteries, but does it work for LiFePO4 chassis batteries? What protects the alternator in that scenario?
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Old 09-24-2020, 03:30 PM   #7
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Originally Posted by Vortriede View Post
That works for AGM or FPbA chassis batteries, but does it work for LiFePO4 chassis batteries? What protects the alternator in that scenario?
I have AGM start batteries and lifepo4 house batteries. As I said, the Victron dc-dc charger supplies the proper voltage to the house batteries, and limits the charge to the house batteries to protect the alternator, in my case 30 amps.
https://www.solar-electric.com/victr...1MGxrBwlmfMNuh
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Old 09-27-2020, 10:11 PM   #8
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Emergency Start Function Details

My original design for the emergency start function duplicated the original behavior of the RV Custom Products battery distribution center; namely, when you push the switch, the interconnect solenoid energizes for one minute and then deenergizes. I decided that I wanted to be able to turn it off if I wanted to, before a minute had passed. That is a trivial change to the code that the microcontroller runs, but then there is the problem of not knowing for sure whether the solenoid is energized or not. I decided that I was going to re-wire things to facilitate an indicator that the solenoid is energized (or not) at the dash. I was thinking of putting an LED up there for the purpose. There are two wires that run from the distribution center to the switch on the dash. My original design had one of these wires grounded and the other going into one of the I/O pins (4) on the microcontroller so that when the switch is actuated, the microcontroller knows to do its business. My plan was to instead, use a ground connection near the switch instead of using one of the wires for the ground leaving that wire free for another purpose, namely energizing the LED. Then, while examining the dash switch, I discovered that it already has a lamp as part of its design, but it was not connected to anything. This was a marvelous discovery! I didn’t have to drill a hole in the dash to mount an LED!!! But I did have to run 12 volts up the wire to the switch and move the connector over by one pin. I simply hooked that wire up to the relay that was energizing the solenoid, adding a fuse for good measure. Now, when I hit the switch, the solenoid energizes and the lamp on the dash switch lights. If I hit the switch again, the solenoid deenergizes and the lamp goes off. If I hit the switch to energize the solenoid and leave it for a minute, it automatically deenergizes and the lamp on the switch lets me know what is going on.

The dashboard switch is a Carling Technologies V3D1WNNB-AFC18000 as far as I can tell. Here is a link to the specs for that family of switches:
https://www.carlingtech.com/sites/de..._datasheet.pdf

The important bits from that spec sheet, as relates to this specific switch, are that the switch circuit is on page 8 and is type 3 and the lamp circuit is on the next page and is type K/W. The switch has two lamps, one for dash illumination (pins 7&8) and one that is an indicator lamp (pins 6&7). The wires from the controller were connected to pins 2&3 of the switch. I moved the wire from pin 3 over to pin 6 which is the pin that energizes the indicator lamp. I connected pin 3 to a ground which I took from the fuse panel that is on the firewall just to the left of the parking brake. The wire that now goes to pin 6 on the switch is connected through a fuse to the relay that energizes the solenoid and the wire that goes to pin 2 on the switch is connected to an input pin on the microcontroller. Here is a diagram of the components and their connections.

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Old 09-28-2020, 08:44 PM   #9
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Excellent writeup. I installed 3 200 amp lithium batteries in my Damon. I'm using a Magnum smart battery combiner to control the charging between house and chassis batteries, but that may change. I like what you did for the aux starting, as I have an intellitec BCC, and just disconnected the ground off the solenoid, totally deactivating the emer start function, otherwise the solenoid would be constantly connected due to the BCC. I used these batteries from Amazon. https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
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