Trying to understand this alternator upgrade by FitRV

This is about the Massive RV charging system upgrade! video posted by FitRV.

I’m trying to wrap my head around the reasoning and observed results. In the spirit of transparency:

  1. his use case is different from mine, so I will be trying to understand it from his POV
  2. his economic situation is likely different from mine
  3. I am not in the fanbase for the channel. It has less to do with the channel than with the things that personally annoy me so I won’t go into that. I will do my best not to allow that to affect my approach to the video’s content.

the rig before upgrading

  • Winnebago Ekko
  • came with secondary alternator for charging, a 170A externally-regulated Balmar.
  • LiFePO4 capacity increased to 20kWh
  • 3.5 EcoBoost engine

the parts, and stated reasons for the upgrade

Here are the parts involved in this upgrade:

  1. Nations 300XM 300A secondary alternator, ~$1,430
  2. Wakespeed regulator option, +$300 (enables CAN communication)

These two together make the Nations 300-XM-WS system. It does not appear separately on the website as a product, but the Balmar version claims:

  • a maximum of 300 amps
  • will produce a minimum of 170 amps continually at low idle speeds
  • maximum output above 1800 engine RPM.

In the video (timestamp 11:10) the owner claimed:

  • continuous 230A going down the highway
  • 130A-150A at idle, depending on temperature

Nations is a reputable and knowledgeable shop and I fully believe their claims can be reproduced in the real world under controlled conditions.

≥100A output at idle

The Balmar was making 40-60A at hot idle (2:50), not enough to run the 100A A/C (3:00). FitRV wants ≥100A at hot idle.

I’ll point out that while idling to charge isn’t great for the engine, it can be especially problematic for direct-injected engines like the 3.5L EcoBoost in this rig. Average cost to walnut-blast carbon deposits from the valves seems to run ~$1,000.

increased output while driving

Charging the 20kWh bank from the 170A Balmar “does take a while to charge up” (2:20). The Balmar would make 150A while driving (30A x 5 batteries, 19:50). FitRV wants more charging current while driving.

not overcharging the battery

After fully charging the bank on shore power (5:20) the Balmar was not smart enough to avoid unnecessarily re-Bulking. FitRV wants to avoid re-bulking and will use use CANbus data to feed the CAN-aware Wakespeed controller to solve this problem (if it is one).


According to a related blog entry:

So How Did It Work?
In a word: Awesome.

Let’s see.

at idle

The bank wanted to reach 14.4V (16:08) and up to 1000A of current (16:20).

With the A/C running (15:20) at idle the system was making net +100W (16:35), just enough to run the 100A A/C and whatever else was drawing power in the rig.

James does not look particularly happy (17:05). He, like me, might have been wondering where the claimed 170A (website) or 130A-150A (verbal) at idle has gone. To be fair, later he did observe the alternator making 212A at idle when cold (24:05).

while driving

“250A or more while driving” (20:15). Screen showed max of 39A (21:50) to -54A per battery, which suggests the 5P cabling isn’t optimized. The outer batteries (#1 and #5) were getting ~50A and the inner ones (#2 and #3) were getting ~40A.

This suggests alternator output was ~225A when the CAN showed the batteries wanted up to 300A (screenshot at 22:01).


The wakespeed seems to avoid rebulking.

Since it takes “a long time” to charge from the original Balmar, it seems to be that it would be reasonable to set the shore power charger so it does not charge fully. Maybe to 13.2v - 13.4v. Problem largely solved. I will also mention that somebody worried about excess charging might not want to run a 14.4v Vabs anyway.

cost / benefit

  1. is +50A at idle and +75A to +100A while driving worth >$1,400 (not including labor), when one already has shore power and solar charging?
    • With an engine that fouls the valves when idled excessively?
    • when fast-charging seems to be entirely discretionary? They only “run the batteries down when we have driving days coming up” (2:25). If one has driving days coming up, it might be worth observing the difference between charging from 10%->100% at 150A vs 250A is 9.6 hours / 5.76 hours. Charging at the average 225A (paralleling issue described above) would take 6.4 hours.
  2. is the avoidance of rebulking worth $300 (Wakespeed upgrade), when one could set shore power Vabs/Vfloat lower for free?1

Given their judgement that the upgrade is “awesome”, I’d assume they think so. Or it was more for fun than anything else (I do things like that sometimes). Or they paid less than what the rest of us would pay if we walked in the door.

Nations is not mentioned on FitRV’s Partners page, but there is a prominent callout (18:20) where the owner gives contact information. Perhaps Nations ate the install cost, or provided the gear at cost, or something more generous in return for the exposure. Dunno. They aren’t saying, and the YT comments are disabled.

misc observations

Perhaps the setup’s inability to meet written and stated output claims at idling is due undisclosed loads, relatively-high state of charge, and/or resistance in the wiring. It certainly can happen, at least with plain isotors and stock alternators. Screenshots of them driving show SoC to be ~70% and Vbatt ~13.4v. Testing with Vbatt around 12.0v would clear up some questions.

At 22:45 James remarks his Victron SCC will re-bulk/re-Absorp if bank voltage drops 0.1v below the setpoint. This restart setpoint is configurable in the Vic and in most other SCCs.


twitter comment thread for this post

  1. setting the solar charge controller and alternator Vabs lower isn’t a practical option, since both solar and driving are time-limited. Keeping Vabs high help keep current rates up. Shore power isn’t time-limited in that sense, because one is assume to be on the pedestal at least overnight and maybe for multiple days.