Connect old power converter to DC to DC Charger for Lithium Battery

[WardM]

I have a 2001 Great West Van RV. It has an old Magnetek 6332 converter for use with shore power. It has no battery charging logic and just passes the converter voltage to the house battery. There is also a battery isolator between the starter battery and the house battery that allows charging the house battery from the alternator when the van is running. 80 Watts of portable solar panels with portable charge controller.

I plan to install a large Lifepo4 battery to power a fridge with a DC compressor and am considering the following:

A DC to DC charger (that has a Lithium charging profile) with both the Magnetek 6332 DC output and the Alternator DC output to the DC input side of the charger and the DC charger output connected to the existing DC distribution panel and house battery. Does this seem appropriate?

The wiring from the house battery compartment to the DC distribution panel is about a 6 foot run but is only 8ga so I'm thinking 40 amps maximum but will likely opt for 30 amps to be safe. Thoughts?

I'm trying to maximize space use in an already cramped van and I can fit a large Lifepo4 battery in the existing house battery compartment and a dc to dc charge beside the power center.

 

[mikefitz]

It has an old Magnetek 6332 converter

This is a simple DC power supply with battery charger option. The output is 'raw' full wave rectified and needs a battery load, ideally a lead acid, to produce a 'smooth' DC . I would think there will be issues feeding into a DC to DC charger without a battery in place.
There is no problem feeding the DC to DC charger from the starter battery to provide engine power to charge the new battery.
Magnetek 6332 converter, from the data I can accesses, seems to have a average output voltage, (the ripple taken out by a battery) of around 13.8 volts with a maximum current of 32 amps. My experiences with DC to DC chargers indicate the input current is 10 to 20% greater than the output current.

I guess the 6332 converter acts as a power supply for 12v appliances when on shore power,

Info, https://www.irv2.com/forums/f54/trying-to-resurrect-a-1986-coachmen-a-162088.html
download the pdf RV Binder1.pdf

I doubt the converter would directly charge a lithium battery without burning out.

My advice would be to purchase an AC battery charger that will act as a charger and power supply, ( Victron IP22 range, https://www.victronenergy.com/chargers/blue-smart-ip22-charger)
Use this to replace the AC section of the 6332 and connect the lithium battery to the output.
The DC to DC converter will look after engine charging.

Mike

 

[WardM]

I know that I can't connect the 6332 directly to the lithium battery and I an considering replacing the converter section of the 6332 with an AC charger.

I still need a DC to DC charger to charge the Lithium battery from the alternator input and I was wondering if I could also connect the DC output of the 6332 to it since I won't have alternator and shore power at the same time.

In researching the Victron 30amp DC to DC charger, it indicates I can have an input range of 10 to 17 volts so the13.8v input from the 6332 would be converted to the 14.4 volts (or 14.6 volts) that the Victron would output to the Lithium Battery.

Other DC to DC chargers I have researched like the Renogy and Kiase products have similar specifications.

So just looking to see if there are other issues I should consider or if this is a possible configuration.

Not opposed to adding an AC charge but just interested if this would work.

 

[mikefitz]

the13.8v input from the 6332 would be converted

Yes , but the 6332 may not provide enough current is the first problem, ( its limited to around 30 amps), secondly the 6332 produces from the AC input a crude full wave rectified 'raw' output. This is normally 'smoothed to 13.8' volts by a battery. A DC to DC converter may not work correctly with this form of input waveform.

Its possible others have interfaced the 6332 to a lithium battery and may be able to offer advice. The 6332 is not installed in Europe, but we have similar units in RVs from the same period, late 199X. The usual modification is to replace the AC converter with a up to date battery charger.

With the DC to DC converter/charger, it will function as you are suggesting, if the DC input is within the allowable range of voltages and the available supply current is high enough.

 

[WardM]

My wiring doesn't support much more than 30 amps (I don't want to re wire yet) so that's not an issue.

When I select a DC to DC charger and get all the pieces installed latter this month I'll test it.

I can't really monitor the amps output by the 6332 but I have a Victron 712 Battery Monitor so I'll see what gets to the battery. I'm guessing it won't be very many amps and I'll need to install a real charger but it only costs some time to test it.

Thanks for your thoughts.

 

[Prerunner777]

My 2017 5th has a WFCO 68100a converter charger 100amp. Its expensive to replace and need it during winter months while trailer is parked inside pluged into shore power. The dc output is smoothed and can function as power supply with no batteries. The problem is not being able to fully charge lithium if needed during summer. If I need to start my gen I want a 60 amp charger to limit run time. A DC to DC charger looks like the cheapest option. After hours of research still not 100% I could connect my convertor dc output to the DC to DC charger and get a proper charge on lithium batteries. Can a DC to DC charge step up voltage to 14.4 if convertor output is in 13 volt range? Any other problems with this idea?