Upgrading Dodge Alternator

[markopolo]

Originally Posted by wincrasher

Actually, by leaving the existing separator in line, I don't quite understand why I need another parallel separator to run from the alternator to the battery bank. ........................

Good point. I wasn't sure what was going on at the power junction block (assuming there is one). I suggested the additional separator to make sure there was isolation between chassis and house batteries.

My setup looks like this:

separator.JPG

It was just a couple of feet of wire and a $70 separator so it made for an inexpensive, quick and easy job. Existing cable to 2nd chassis battery was 1 gauge.

Booster's sketch eliminates a 2nd isolation device and gets rid of that 8 gauge wire. Check the wiring to the fridge to see if it needs to be relocated.

[wincrasher]

Thanks all. It's starting to gel, but I have a ways to go.

Let me ask you a remedial question.

My existing alternator is rated at 130 amp.

The charging circuit for the house batteries is 40 amp. Since my lithium bank has such a high acceptance rate (the whole bank should be ~320 amps), why is this CB not tripping? Is the cable limiting the amps going to the bank, so we remain under the trip threshold? Or is there just not nearly as much output out of that alternator for all the circuits shown on the diagram?

[booster]

That is a good question. When you say 320 amps, is that the recommended charging amps for the batteries?

What are you seeing for charging rates on BMK? Perhaps the batteries are near full, or maybe the alternator is maxed out at idle. If you have 40 to the batteries and another 15 to run the van, and maybe another 15 to the starting battery, you could easily be above the idle output of the alternator. The alternator could also have a bad diode or two, and thus low output. A replacement alternator may also be running at lower than desirable voltage, 13.8-14.0 volts used to be very common, and many replacements still seem to run there. Your current isolator is also going to drop the voltage about .7v, so you could be too low to charge lithium well. A #6 will have some voltage drop also, but should be pretty good for 40 amps.

If you are seeing over 40 amps to the batteries for longer periods, then you have a bad breaker. Most breakers will run at overcurrent for some amount of time so be patient.

[wincrasher]

No, that is their max rating. Each battery is rated at 80 amps max acceptance, 100 amps max discharge.

I don't seem to have trouble charging them to mid-14 volts on the display. It's just that the amperage is fairly low, but not unexpected. I was just curious as to what is holding it back, as theoretically the alternator should peg on output since the batteries could take all that it could deliver. But that never seems to be the case. It certainly didn't on my Travato - same thing 35-40 amps was max. I've yet to do a test where I just idled the engine for several hours to attempt charging to 100%. My cross country drive last month certainly had enough time to do that, but I didn't have the BMK installed then - resting voltage on the batteries was 13.2-13.4 most of the time.

I also wonder what would happen, if I installed the big alternator, and then closed the switch to the house bank. Would the old 160a isolator be overloaded, or would it humm along just fine since there were low amp loads downstream of it?

[booster]

Are these the same batteries that were in the Travato? If so, and they did the same there, it would sound like the batteries are doing the limiting and perhaps the manufacturer could shed some light on the situation.

Once you know what voltage you have at the batteries, as you should with the BMK, the manufacturer should be able to tell you how many amps they should be accepting at that voltage. It may be that the voltage is so low, that you are barely above the voltage of the batteries themselves at that state of charge.

How much do they take on shore power?

[wincrasher]

Yes, same type. They take 125-135 amps from the Magnum 2812.

[booster]

How does the charging voltage at the batteries compare between the Magnum at 125 amps and the alternator at 35 amps?

I am starting to think what you may have is a big ground path resistance. Voltage drop can happen in either positive or negative and it will affect the charge rate the same. If you are seeing decent voltage on the positive of the batteries to ENGINE ground, then check to see if you have any voltage from the CHASSIS ground to the engine ground. As was mentioned earlier, it is very common to need to upsize the engine to frame ground strap, and they are also famous for corroding or coming loose and giving high resistance. Couple a ground resistance with the isolator resistance, and the batteries could be seeing quite low actual charge voltage.

[wincrasher]

I'd have to make more observations to tell you.

On the BMK, since I'm using the CC/CV profile, the voltage shown is starting at whatever SOC you happen to be when you start - mostly 12.9-13.1. The voltage will show low, and the amps going in very high. As the voltage climbs, the amperage drops. I have it set off to shut off at 15 amps which is pretty close to 14.6 volts.

Of course, I haven't made any such observations yet doing alternator charging except for a brief test when my bank was at 13.1 volts. At idle, with the refrigerator and the ventilator running, the BMK was showing 27-30 amps. When I revved the engine, it would shoot up 37-40 amps. So the load of devices would add 4-6 amps at the time.

I have gobs of capacity though - it's been unplugged since sunday. I have the ventilator on and the fridge running. Last night the batteries were still at 78%, and my solar is giving around 550 whr per day, extending the death spiral quite a bit.