Replacing OEM batteries with LiFePO4's

wade5979

New member
I thought of the space under the Murphy Bed too but then I noticed the head of the mattress swing a compound arc into that area. I also thought about a battery blanket for the one under the hood but how much of the extra energy will be lost warming it. The majority of the time I'll be in warm weather areas so I'd have the energy most of the time.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
What year is your MB? - newer than 2012? Mine has the power bed, and the interior compartment has a removable plywood top, so the bed can't swing an arc through it! But I don't know what size it is - the RV is in storage for the Winter, so I can't check it out without going over to the building and going in with a flashlight and a tape measure.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
That's the difference. Mine's the earlier power bed - the compartment is big and the bed doesn't impinge on it. But of course if I used that area I'd be loading weight on the slide, and I'd need wiring that could move with the slide.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I have a small reality check question here. I want the ability to control when the alternator charges my batteries - I don't want it charging any time I'm driving. I'm thinking the the easiest way to do this is to put a switch in the circuit that controls the isolator solenoid, since the alternator output goes through the solenoid to the battery bank. Does anybody see any downside to simply making the solenoid coil switchable?
 

turbopilot

New member
I have a small reality check question here. I want the ability to control when the alternator charges my batteries - I don't want it charging any time I'm driving. I'm thinking the the easiest way to do this is to put a switch in the circuit that controls the isolator solenoid, since the alternator output goes through the solenoid to the battery bank. Does anybody see any downside to simply making the solenoid coil switchable?
I think it is an excellent idea and should be a standard feature. If there is any kind of electrical anomoly in the 12 volt system of the camper it would be important to isolate the cab 12 volt system from the camper 12 volt system. As designed any time the the voltage of the cab 12 volt system goes above 13.3 volts for 12 seconds the systems are combined with no easy way to separate them.

That is why I suggested earlier that the IRD be replaced by the Blue Sea ML-ACR Automatic Charging Relay. This relay comes with a switch that allows the systems to be combined and disengaged automatically, or manually combined or manually disengaged.

This is the device used in the EarthRoamer. In the automatic position the 12 volt systems were always combined as long as the combined system voltage exceeded 13.2v. Once the camper battery dropped below 13.2v, the cab battery would be taken off line automatically to protect that battery against inadvertant discharge. Anytime the rig was plugged into shore power with the ACR in automatic the camper charger would simultaneously keep the cab and camper batteries charged with both systems combined. I have not had a chance to see if the Blue Sea ML-ACR will fit in the same place as the IRD.

 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I was thinking of simply breaking the IRD output circuit that controls the solenoid coil, and bringing the wires back to where my other control circuitry is. I could simply put a switch there - it'd be easy enough to watch the battery monitor and simply throw the switch manually to defeat the IRD/solenoid's normal functionality. I could also tie it into the internal control relay in my battery monitor and have it automatically open the isolator (and thereby disconnect the alternator output from the house batteries) whenever the battery monitor reached whatever "almost 100% SOC" point that I choose.

I've been breadboarding a control circuit over the last week - the battery monitor's internal control relay goes to 2 relays, one closed by the Sprinter ignition 12v and the other by the presence of shore power or generator AC - if neither is present, I don't need to sense battery voltages and deal with charging. But if either one is present, the charge/no-charge signal goes to a temperature monitor (so I don't try to charge when the batteries are below freezing - that damages lithium batteries) - handily enough, the temp monitor has a relay that could switch the isolator circuit as above - it could also switch my charger/converter. Then I'd have an entirely automatic charge control circuit for not a lot of financial outlay.
 

turbopilot

New member
I was thinking of simply breaking the IRD output circuit that controls the solenoid coil, and bringing the wires back to where my other control circuitry is. I could simply put a switch there - it'd be easy enough to watch the battery monitor and simply throw the switch manually to defeat the IRD/solenoid's normal functionality. I could also tie it into the internal control relay in my battery monitor and have it automatically open the isolator (and thereby disconnect the alternator output from the house batteries) whenever the battery monitor reached whatever "almost 100% SOC" point that I choose.

I've been breadboarding a control circuit over the last week - the battery monitor's internal control relay goes to 2 relays, one closed by the Sprinter ignition 12v and the other by the presence of shore power or generator AC - if neither is present, I don't need to sense battery voltages and deal with charging. But if either one is present, the charge/no-charge signal goes to a temperature monitor (so I don't try to charge when the batteries are below freezing - that damages lithium batteries) - handily enough, the temp monitor has a relay that could switch the isolator circuit as above - it could also switch my charger/converter. Then I'd have an entirely automatic charge control circuit for not a lot of financial outlay.
Interesting project. I agree switch the "IGN" wire to the IRD solenoid makes a lot of sense and should be easy to do.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Yep, that's the way it seemed to me. Harder is how to switch the charger off, as it doesn't have remote power switch capability. Lifting the 12vdc output would require a big solenoid similar to the isolator; lifting the 120vac input may be easier. Originally, I was going to install a honking big solenoid and reroute either the alternator or the charger line so I could lift them both via the solenoid - then I got a wiring diagram and realized that the alternator was easy to handle. Last week I hit Radio Shack and my parts bin - I grabbed a DC power supply and a prototyping board, stuck a few relays and LEDs on it - found that playing with parts makes it WAY easier to think things out than drawing diagrams and wearing out my eraser <g>...
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Those are pretty cute, and not horribly pricy - thanks, I never thought of anything like that, but it'd add a lot of flexibility.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
You're right, it's way too small to BE a power relay - but it could work as a driver for a power relay. For example, if a power relay coil takes 6-7A, that relay would have sufficient rating to switch it. It's the same situation as with the relay on the temp controller I've been experimenting with - that's also a 10A relay.

The control circuit I'm playing with starts with the internal control relay in my Victron battery monitor - it's highly programmable, but it'll only handle 1A @ 16V max - much too small "to do much", but it's perfectly usable as a control relay. It analyzes battery SOC and it has to control a circuit that knows that I've either got alternator output (or at least, M-B ignition) or shore/generator power, and that the battery temp isn't too low for charging safety, and it has to switch... something <g>... And that's where I'm at just now - deciding just what's the easiest way to switch both the alternator output and the charger output.
 

Boxster1971

2012 Sprinter 3500 Ext
You're right, it's way too small to BE a power relay - but it could work as a driver for a power relay. For example, if a power relay coil takes 6-7A, that relay would have sufficient rating to switch it. It's the same situation as with the relay on the temp controller I've been experimenting with - that's also a 10A relay.

The control circuit I'm playing with starts with the internal control relay in my Victron battery monitor - it's highly programmable, but it'll only handle 1A @ 16V max - much too small "to do much", but it's perfectly usable as a control relay. It analyzes battery SOC and it has to control a circuit that knows that I've either got alternator output (or at least, M-B ignition) or shore/generator power, and that the battery temp isn't too low for charging safety, and it has to switch... something <g>... And that's where I'm at just now - deciding just what's the easiest way to switch both the alternator output and the charger output.
Good points I hadn't considered.
 

Graphite Dave

Dave Orton
I looked over the spec sheet on these smart relays. Looks like they are only designed to handle a 10A load. That's not going to work as an isolation relay for batteries and alternator.
Was not suggesting it as a power relay. Just for the control logic instead of a custom designed circuit.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
That's interesting reading. Most complaints are for slow delivery or non-delivery. I bought SmartBattery SB100's, and I also had a problem with late delivery, though not months late. Several complaints mention difficulties with communication. I experienced this. It was hard to get answers to phone calls, and there seemed to be little real tech support. Their website's chat function never was functional - I'm sure I tried 20-30 times, finally out of curiosity to see if there was ever a response.

Luckily, I think there are now more choices of battery sources, both drop-in and cell supply sources - though I've also read on various forums that there have been delivery and quality problems with some of the cell suppliers. So caveat emptor!!
 

Eugene Rider

2016 Unity TB
Wow, have I learned a lot from this blog, thanks to all who contributed. I ordered a true 2016 Unity TB (fog lights standard, wind stabilization) , be delivered in April or May.
I got the solar panel package and will do some added extras that I did to my 2004 Coachhouse. I have 2 100 watt solar panels that are portable so I can find the sun in a tree filled campsite. Made it so that I use a 12 amp extension cord to plug into my unit with regular plugs, the neutral being positive and the ground being negative. Works well. I'm love gadgets and will be doing the LiFePO4 conversion. I live in Eugene, 15 minutes from AM solar, have meet these folks and they are great so will be getting info from them.
My thought was to install the Sprinter-Van-Dual-Alternator-Kit-with-270-Amp with regulator just for the LiFePO4 batteries and leave the stock alternator for the van. My thought was if I get 400 amp battery pack, would I need the generator? The only time in 10 years with my Coachhouse I use the generator is for the microwave, once to take a nap during the day in 118 degree weather for the A/C and often for the wife's use of the hairdryer.

Would I be foolish not to order the generator for resale or??
Pro would be a place for the batteries and lose some weight.
 

Top Bottom