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JoeCastor · 02-14-2025, 12:22 PM

Lots of DC-DC questions, but they don't answer my question.
I have a Precision Battery Isolation Manager (BIM) that I disconnected the ignition wire from to protect my alternator (as advied by Precission tech dept) because of the 200 amp draw from my LFP batteries.
Question - is there any reason I can't put a DC-DC chrger at the BIM, using the ignition wire from the BIM and connect to the chassis battery (alternator) treminal and the house output terminal? It seems that every thing is right there.
All help and advice appreciated.

Tony Ramirez · 02-14-2025, 12:51 PM

My BIM is the Precision Circuits 00-10021-00. After talking to PC directly, they had me take off the "brain" of that BIM(black sealed box.) Used the Ignition wire to trigger the DC2DC Charger. Left everything else in place. Unplugged the "Gen Set" wire & abandoned it. That way I still have the "Boost" function, just not the charge aspect. I then ran a cable from the Chassis Post of the BIM to the IN of the DC2DC Charger.

d23haynes57 · 02-14-2025, 01:00 PM

How much Lithium battery do you have to get a 200 A/H draw and what size is your alternator? What size DC to DC charger are you looking to install and what other loads are on your house battery system? Do you really need alternator charging? Can you supplement with generator and inverter/charging? Could be other options.

Tony Ramirez · 02-14-2025, 01:41 PM

To add to d23's point, I also added a remote control to the DC2DC charger, thinking I didn't want my alternator overworked while idling building up air, rolling out of camp, so forth. I would click it on once I got on the freeway. (I know, I overthought it). During my summer cross country trip, I didn't even turn on the DC@DC, solar did it all. The cross country trip during the holidays, I did use the DC2DC though.

JoeCastor · 02-14-2025, 02:54 PM

d23haynes57,
I have two 300AH LifePo4 in parallel. These batteries each draw 200 amps (and 200 amps in parallel). My alternator is a 160 amp. I'm currently running without any charging during travel. In the summer it's fine because I'm running the genset for A/C, but running all day and then an unexpected night without a hookup and noise issue running the geset puts me past my limit. My coach is mostly all electric except for cooktop and aqua-hot. So, I want to keep my batteries topped up as much as I can. That's what they're these for.

d23haynes57 · 02-14-2025, 03:34 PM

Quote:

Originally Posted by JoeCastor

d23haynes57,
I have two 300AH LifePo4 in parallel. These batteries each draw 200 amps (and 200 amps in parallel). My alternator is a 160 amp. I'm currently running without any charging during travel. In the summer it's fine because I'm running the genset for A/C, but running all day and then an unexpected night without a hookup and noise issue running the geset puts me past my limit. My coach is mostly all electric except for cooktop and aqua-hot. So, I want to keep my batteries topped up as much as I can. That's what they're these for.

Are you sure that your batteries are pulling 200 amps off that 160 amp alternator? Does the wiring support it. Has this been tested? Still, 160 amp alternator is light for that size battery bank and will still be tasked with a 60 amp Dc to DC charger which is really a minimum for that size battery. 60 amp puts you at a 10 hour charge rate. My suggestion would be to upsize the alternator. Going to a 260 amp or would allow you to direct charge. Depending on engine alternator configuration (belts and brackets) you may be able to bolt up to 320 amps.
What do you have for a charger, or an inverter charger, and generator? A 3000-watt inverter with a 150-amp charger would be ideal. 4-hour charge rate. This can supplement the alternator charging until batteries approach full charge and then alternator can maintain charge and moderate loads such as refrigerator. The larger alternator will also allow the inverter to support one AC after the batteries are charged. For house battery charging control I prefer the automatic voltage-controlled relays. The Blue Sea 7622 is amongst the best.
https://www.bluesea.com/products/762..._-_12V_DC_500A
the real beauty of this is the ability to override and force connect or disconnect both remote electrical or mechanical in the event of a failure. This provides ultimate flexibility for charging or isolating the battery banks based on using generator, shore power or engine alternator. The remote switch illuminates to indicate status.
My rig has a 270-amp alternator and uses the Duvac (diode block) system for alternator charging of the house batteries. This is working very well to charge a 900-amp lithium battery bank. The diodes and cabling provide the needed current control as the voltage sense for the alternator is on the chassis batteries. I see peaks of about 160 amps dropping down to ~120, quickly. As the batteries approach 80% they current will drop down to ~60-80 and then when full the battery BMS turns charging off. Works this way on alternator or the inverter/charger. When on shore power and the charger drops to 13.6 volts, I close the boost relay and that charges-floats the AGM chassis batteries.