2 BB Lithium Battery, LI BIM 225, DC To DC, 2018 Forester

[greghayes655]

I am changing out my 2 Lead Acid batteries for 2 BB Lithium 100 AH batteries in a 2018 Forest River Forester 3051S (class c). The Forester has a Precision Circuits Battery Control Center with model ending in 701A. I spoke with Precision Circuits and it is a very easy swap in this BCC to install the LI BIM 225. I doubt it would take more than an hour to do the swap. It certainly is the easiest way to install lithium in my rig but as many have pointed out using a DC to DC charger is probably a better way to charge the batteries. So I have an idea for a hybrid system using both DC to DC and LI BIM.

Using the LI BIM has one advantage that I like. I’m concerned with just two BB Batteries it may be hard to start the generator if the BB battery bank is partially discharged. Even Battleborn suggests using 3 of their batteries if you want be be certain you can start the on board generator. But I only need 2 lithium batteries for my needs and I would like to keep them in the stairwell where the lead acid batteries were installed. Because of my concern about starting the generator, I want to be able to easily connect the coach and chassis batteries to help with generator starting and the LI BIM 225 allows that using the emergency switch located on the driver seat in my rig. I also think I want the option of alternator charging in an emergency. I like the idea of a DC to DC charger to be more certain my alternator won’t overcharge the BB Batteries so I’m looking for a way to accomplish all 3 of my goals.

My E450 V10 has a 155 amp alternator according to Ford. Battleborn recommended that I install the lithium batteries when they arrive and use a clamp ammeter to test how many amps is flowing to the batteries. I probably have to do that using the manual switch to connect the battery banks together because the stock BCC-BIM probably won’t connect the new BB batteries to the alternator due to voltage differences. Battleborn told me when I run this test if there are 120 amps or less it would be ok even though they state 100 amps max charge rate for a 2 battery system in their specs. Now with a 155 amp alternator and factory wiring I’m thinking the coach batteries probably wouldn’t see more than 100 amps but why chance it. So DC to DC is probably a better alternative for charging the coach batteries. When I spoke to Precision Circuits they told me if I leave the stock BIM and solenoid in the BCC and simply remove the Orange and Red Wires from the solenoid that would disable the original BIM but leave the functionality intact to connect the battery banks in an emergency. So installing a DC to DC charger and removing just two wires in the stock BCC accomplishes two of my goals (safe coach battery charging and ability to connect battery banks in a emergency). Has anyone else done this?

I think having a DC to DC charger and the ability to connect the two battery banks as noted above is a pretty good solution and probably is what I will do but it does not allow alternator charging in an emergency because the stock BIM in the stock BCC would never connect the house batteries to the alternator due to voltage differences even if I were to reconnect the orange and red wires.

So now I am thinking of a hybrid system where I would install a switched DC to DC charger and the LI BIM 225 but I would disable the LI BIM 225 via a toggle switch so I could connect it in an emergency if the DC to DC charger failed or if I needed to connect the house batteries to the chassis battery to help start the generator when using the switch on the driver-seat. I was thinking of using a toggle switch on one or more of the wires on the LI BIM 225. Does anyone have any ideas if this will work? The stock BCC BIM consists of two separate parts, a solenoid for switching the power to and from different sources and the BIM itself. So I understand how that solenoid still functions to connect both battery banks if I remove only the orange and red wires. But the LI BIM 225 is a one piece unit with a few less wires involved so I’m not sure it can be bypassed but still retain ability to connect both battery banks manually by the driver seat switch. I was thinking of placing a toggle switch on the power (red wire) leading into the LI BIM which could be turned on in an emergency giving full functionality to the LI BIM 225 when i need to use the emergency driver seat switch to help start the generator. My DC to DC charger would not be connected via ignition but via a switch so it could be disabled at any time. As added benefit, with the DC to DC charger switched off, the LI BIM could be activated when on shore power which would keep chassis battery charged. Any ideas or thoughts?

BTW I already purchased the lithium converter upgrade for the PD4060 power center, the BB batteries and the LI BIM 225. Next to purchase is Victron battery monitor and a DC to DC charger and I’m leaning toward one of the Renogy models.

[JLeising]

Wow! You have a lot of contingencies planned in.

I guess you are using the LiBIM as a backup means of charging your house batteries off the alternator should the dc-to-dc converter fail. You could just use an on/off switch instead of the momentary battery “emergency start” interconnect switch on the existing interconnect solenoid. The BIM adds voltage sense (insures there is a sufficient voltage differential) and it cycles on and off (something like 15 minutes on then 20 minutes off to avoid overheating the alternator), as I understand it. Not sure this functionality is necessary for an emergency backup situation (you could manually switch it on and off every 15 minutes or so). See below about concerns wrt connecting the two systems together, however.

I have had no problem starting my generator off of two paralleled Battleborn 100 amp hour batteries. I guess, if there was to be an issue, it would be the internal battery control circuit sensing excessive current draw and cutting the battery power off. Using the emergency start switch to activate the battery interconnect solenoid (or the relay in the BIM) should allow the chassis battery/alternator combo to be used to start the generator. If this were to occur in my unit, I would probably disconnect the Battleborns first, then activate the interconnect solenoid, as personally, due to the inherent voltage differences of the two battery chemistries, and the potential for very large current surges, I don’t like the idea of directly connecting the chassis/alternator circuit to the house LiFeP batteries.

I understand you are intending a manual switch supplying 12 volts to the ignition trigger of the dc-to-dc converter. I would alternatively suggest wiring it to an ignition signal, with a switch that allows you to disconnect the signal should one of your emergency backup situations require disabling the converter. Then charging off the alternator through the converter would be automatic, and you would maintain the ability to disable (not activate) the converter should some (abnormal) situation require it. On mine, an ignition signal is available in the BCC and I tapped into that signal for my dc-to-dc converter.

FYI, Jim

[greghayes655]

Thanks Jim, the red wire currently connected to the existing BIM is an ignition activated wire and that’s the wire I was thinking of inserting a toggle switch on. It connects to the IGN terminal on the LI BIM 225. What I don’t know is if the LI BIM 225 maintains its current setting when powered down or if it opens all circuits. The switching mechanism is a simple sliding copper plate per the install instructions. So I’m thinking it’s isolated or it’s not based on the voltage readings it’s getting and I’m concerned when I remove power if it’s not isolated the switch will remain in its last position. I don’t know if it acts like the solenoid where you remove power and it’s open. The instructions say when power is removed it’s either open or closed but there is no further explanation of what that means.

I realize in terms of simplicity I should either use just the LI BIM or the DC to DC charger. Retaining the stock BIM and solenoid in the BCC and the ability to connect the battery banks is so simple to do thanks to the pointers from Precision Circuits.

[JLeising]

You may well be right - the lithium BIM may well stay in its “on” or “off” state unless it is activated. My understanding is that coil activation is dependent on on/off time and the presence of sufficient voltage differential to allow house battery charging. I did not use a LiBIM in my install, so I’m not particularly knowledgeable about it.

[JohnArm]

Very similar setup. Replaced two 240 aHr 6 v batteries in series with two 100 aHr Lithium in parallel. I also have installed the LI-BIM 225 as a replacement for the BIM-225. Last week after several cloudy days I work up to very low coach batteries. The generator would barely crank. If it were not for the emergency override I would have been in deep poop. When the generator came online the coach batteries were pulling 79 amps. I'm not sure how the alternator would have handled that.
There have to be a better solution to protecting the alternator. I am planning to double the battery bank to 400 aHrs but I'm still researching alternates to using a DC-to-DC Charger. RV With Tito posted a YouTube solution where he used male/female connectors at the DC-to-DC Charger such that if he needed to connect the engine battery to the coach battery he would do it manually with the connectors. ref:

https://www.youtube.com/watch?v=lvOYUfSBlmM&t=361s