DC-DC charger

[slomobile]

Recently saw this https://www.mpja.com/Adjustable-DC_DC-B ... /36843+PS/ and thought it might be nice installed in the van to give the chair a rapid top up charge between places on busy days.

Would like opinions on suitability for that limited purpose, and ideal voltage and current limits for 75Ah MK gel at 38C. 10min - 1.5hour random duration. I know it isn't a proper programmable 3 or 4 stage charger. But its only $25, up to 22A, adjustable, and useful for other purposes like running my CPAP while camping.

At the end of the day when you just want to be done and home, but your chair is slow, stretching out the minutes.
Or 3rd day camping with no mains AC, and no fuel to idle through the night powering inverter and stock chair charger.

I'm willing to add a single 24v Anderson connector to the chair, but want to avoid the series/parallel plugs w jumper. The new 270A Euro 6 ECM regulated alternator tends to keep voltages on the low side, making auxiliary charging complicated.

[shirley_hkg]

What voltage is your alternator ?

[Burgerman]

I charge as I drive and do so from a 12V alternator inside my van.

Been doing that for 2 decades. I wear out my batteries at my local airfeild (hobby stuff/planes grass field) in say 3 or 4 hours. It takes me about 20 mins to drive home. Thats enough to put back at least half of what I took out. Generally charges at around 60A or a bit more initially, gradually drops off to way less during the drive back. By the time I exit my van they are good to go out into town in an evening.

So works pretty well. No need for energy wasting and slow charging via low power step up devices. Tried that. Direct alternator charge works much faster. Now this will not give a full charge unless you run the engine all night. But for the odd day in your van that doesent really matter. It can wack loads back in fast. After say 1 hour they will be about 95% full. That other 5% will take 8 to 12 hours. Do that when home.

This page was last updated 14 years ago...
https://www.wheelchairdriver.com/faster ... arging.htm

JUST read you dont want to do that...
Then yes that will work. But will take a while and get super hot! Even if its 90% efficient thats 180 watts of waste heat!
Set it to 28.2V. As many Amps as it will do up to say 30. Dont charge at that voltage for above 10 hours. Once current drops to say 3 or 4A its 95% done. Not completing the charge is OK as long as it gets a really complete 20+ hour charge (includes floa)t at least once or twice a week.

[slomobile]

The alternator is exactly this model https://www.nationsstarteralternator.co ... -270xp.htm on a 2015 Ram Promaster 2500 window van w/rear ramp.
The output voltage is entirely controlled by the Engine Control Module(Unit) ECM(ECU) according to Nations. It expects a single AGM battery around 900CCA like an Odyssey Group Size 49 950 CCA 0754-2020. The ECU has an algorithm that dumps a lot of current back into the battery at a rather high voltage for a few minutes after startup, then settles down to a maintenance voltage. I haven't measured this new alternator yet, but the 220A stock alternator output as low as 13.2V while cruising at 60mph(100kph) with minimal electrical loads and up to 15.4 right after startup. The stock alternator failure was due to an exploded overrunning clutch pulley spring which cut the belt.

Reason for upgrading: they wanted $1050 plus $80 core charge for a stock replacement. This was $770 outright and I get to keep the old stock unit and replace the pulley to have as a spare, or maybe connect to an external regulator and free lawnmower motor for backup power.

Installation was $1200 labor plus the $770 alt, plus another $300 for pulleys and belt. After the installation, the engine had a loud tick it never had before. At pickup, gastank was empty. It was nearly half full when I had it towed in. They admitted to driving it around the lot without a belt. I bet they let it just idle to overheating wrecking the motor. $9000 to swap in a rebuilt motor and 10 weeks lead time. A 122k mile 2015 van for which I paid $40,000 less than a year ago. A dealer, knowing nothing of the engine trouble offered me $17,000 for it. I'm wondering if its time to cut my losses and pass the time bomb of an engine onto some other unsuspecting fool, or just bite the bullet and be all in on fixing everything on this lemon.