LifePO4 upgrade

[Rorobert]

Yeah, thinking about this, and I guess I really don't want anything over 30 amps since it's a 30 amp system, do I? The largest fuses I have are 40 amp for reverse polarity and something else. How would it be if I connect the hot from truck and the hot from solar panel to the 6 gauge that goes to the rear, which is basically the way it is now. then put in a 30 amp DC to DC under the hood for the aux.12v back. I remember that I did put a 30 amp self resetting in that line before. Then I wouldn't even need that manual reset breaker by the battery would I? Or would I just put it where the 30 amp breaker is on trailer? Or do the amps even matter. I have 145 amp alternator.

 

[Lou Schneider]

Yeah, thinking about this, and I guess I really don't want anything over 30 amps since it's a 30 amp system, do I? The largest fuses I have are 40 amp for reverse polarity and something else. How would it be if I connect the hot from truck and the hot from solar panel to the 6 gauge that goes to the rear, which is basically the way it is now. then put in a 30 amp DC to DC under the hood for the aux.12v back. I remember that I did put a 30 amp self resetting in that line before. Then I wouldn't even need that manual reset breaker by the battery would I? Or would I just put it where the 30 amp breaker is on trailer? Or do the amps even matter. I have 145 amp alternator.

We're talking about tripping a 30 amp breaker on the 120 volt side. Everything else you're talking about are on the 12 volt system including the 40 amp reverse polarity fuses.

When you're talking about power there's a 10:1 ratio of current between 12 volts and 120 volts. If the converter is putting out 40 amps on the 12 volt side it's drawing 4 amps (approximately) from the 120 volt line.

 

[Gary RV_Wizard]

Or do the amps even matter. I have 145 amp alternator.

They matter. Your battery is rated at 300AH, though apparently the BMS limits the in/out to 200A. That means a depleted (near "dead") battery will try to suck 200A from any source that connects to it. That's almost a dead short from the perspective of that 145A alternator. And even if the alternator can survive it, the trailer plug and its wires cannot. Fortunately, the tow vehicle wiring for the brake and the Aux 12v will be protected by a fuse or breaker somewhere in the tow vehicle (assuming the installer didn't mess up!) and will blow or trip first. However, it's a whole lot easier if you have a dedicated, resettable breaker or a charge limiter device out somewhere that is readily accessible.

Realistically, after you've been camping a couple days off grid, that battery is going to low on charge, so a high initial amp surge is quite likely when you hook up to move on to the next place.

 

[Rorobert]

OK, I'm pretty DC electric dumb, but I think I'm learning alot here. How's this....I've never had a problem with my alt. to any trailer. In diagram I show going from my alt. & solar panel (both 10 gauge) in to a DC to DC charger on the front bulkhead of my trailer in storage area. Then 6 gauge out and down to original 6 gauge with butt connector, then back to LifePO4 +pos., then +pos. out to existing switch and on to control panel and -neg down to -existing -neg. busbar. Where would I need to add fuses or breakers, if you think this works., and wouldn't a 60 amp DC to DC be too much for that 6 gauge wire, maybe I could use a 40 or 50 amp DC to DC instead.

 

[Isaac-1]

The issue you run into with long thin wires is voltage drop, which itself becomes a charge current limiting factor if you don't have a voltage boosting DC-DC charger in the circuit.

 

[Rorobert]

Are you saying the 6Gauge is too small for that 14 foot run, or that I need a larger amp charger? I thought 6 was only good to 55 amps.

 

[Isaac-1]

This is where things get complicated as we have to ask how many amps are going to be flowing through the wire, if you have a voltage boosting DC-DC charger this can (and often will) be higher than the number of amps going into the batteries. Keep in mind Watts=volts x amps. So that when a voltage boosting DC-DC charger is supplying lets say 50 amps at 14.4V into the battery this equals 720 watts of power, but if the long supply side charge line is small enough to cause the voltage on the wire to drop to lets say 11 VDC from an alternator putting out say 13.8VDC, then (assuming 100% efficient charger for ease of demonstration, reality its likely closer to 90% efficient) we get something around 65+ amps on the wire (720/11), actually a bit higher in real life, lets say 70 amps on that chargeline wire, while only 50 amps (at 14.4VDC) is flowing into the battery itself.

p.s. note the actual voltage drop on the charge line will depend on its length, gauge, and amps, and will vary from one vehicle installaiton to the next

 

[Isaac-1]

Those are regulations for Australia, your avatar suggests you travel in the US and Canada, so really should not be concerned about what Australia requires