Major Battery Charging Configuration Via Vehicle Alternator

msiminoff wrote:

- I have a manual disconnect switch (rated 300A con't) instead of a separator, solenoid, or other controller. This is the easiest and most reliable way for me to choose when to have the truck & TC electrical systems connected.

I might go this route too in the future. I already have the switch (Blue Sea).

nobody said wire the house batteries to the starter

the idea is to supply large wire and make the house batteries the primary 'charge path' and voltage sense, instead of the engine/chassis battery

MrWizard wrote:
just becomes he suggests that "you could have some fun" by modifying your charging system with the field control POT

does not mean he was wrong about using heavy wire ... (snip)

Nowhere in my previous post did I mention cabling or criticize his cable sizing recommendations.

MrWizard wrote:
... and making the house batteries primary and the chassis battery secondary for the RV/motorhome
as the house batteries see far more use and abuse than the chassis battery

Unfortunately, the loads imposed on the typical MH engine starting battery(s) and the charging profiles required, are different than loads and charging profiles on the house battery(s), as stated above. Sure, you can use the house batteries to start and run the MH engine, but you'll dramatically shorten their life by imposing repeated, high amp loads (upwards of 400 amps and more) on them.

MrWizard wrote:
BTW .. his feild mod will work and give you total manual control

Again, I never implied tapping the feild wouldn't work... sure it will work. But how many forum members do you think are savvy enough to successfully pull-off such destructive & irreversible mod on their $300 alternator? Not to mention the meticulous babysitting required to prevent destroying your batteries. You need only visit ANY starter & alternator rebuilder and they'll be happily explain why it's not only a foolish modification, but nearly impossible given the compactness and complexity of the current designed units.

I have never understood why RV owners tolerate the puny charge wiring that most manufacturers provide. My setup is similar to what Mex' describes and I can confirm that proper wiring between the alternator and TC/TT/MH house battery does indeed eliminate many of the issues RV owners have with regard to keeping batteries topped-up while driving.

- I use fuses (I have never blown one, though I do carry spares) instead of circuit breakers.
- I have a manual disconnect switch (rated 300A con't) instead of a separator, solenoid, or other controller. This is the easiest and most reliable way for me to choose when to have the truck & TC electrical systems connected.
- The cables (yes, both + & -) from my alternator to the (2) truck batteries are 2/0 ga.
- The cables from the truck batt' all the way to the camper batt' are 2ga.
- I have a single 180A alternator from DC Power.
- The alternator is voltage regulated by the ECU, charge voltage is 14.2-14.7 depending upon ambient temperature.
- I have a dash-mounted digital volt/ammeter in my truck. When the house batteries are at low SOC, I commonly see an initial charge current in excess of 100A @ 14.7V... even at idle.
- This configuration allows me to easily charge the house batt's to 100% SOC while also running the fridge & H2O heater (on 12Vdc or 120Vac via inverter )or any other appliances while driving.

Cheers
-Mark

MEXICOWANDERER wrote:

• Forget about what you learned or believe
• Disconnect charging lead wires from vehicle alternator. This means all of them
• Run a huge wire from alternator to an ACCESSIBLE Circuit Breaker rated 200% of rated alternator output amperes
• From this breaker continue to HOUSE batteries, same gauge wire
• With a 130 ampere alternator I would use FOUR GAUGE WIRE, the entire distance
• With a 270 ampere alternator TWO AUGHT wire the entire distance
• Run an equivalent gauge wire from the engine block to house battery negative
• At house battery positive use minimum 100 amp rated separator I would choose 200 amp and run the charge lead wire to the disconnected original alternator output wires.

Well good suggestion for someone wanting to increase the charging capability. Heavy wires are good but this setup is not for the average RV.

The average RV can use a lot of house loads while driving and you don’t want to drag down the chassis battery while driving. So the alternator needs to be connected to the chassis battery and then use a solenoid isolator to the house battery. Control the solenoid with a BIRD or bidirectional BIRD and if the house batteries drop the chassis battery voltage to low the house battery will be disconnected until the chassis battery reaches an acceptable voltage. The priority on charging must be the chassis battery and everything that runs off of the chassis battery.

Mex, Haven’t you posted that many alternators are not very good quality and offered suggestions on what to use? If so then maybe the first step should be to make sure the alternator is capable of delivering it’s full rated output.

MEXICOWANDERER wrote:

• Forget about what you learned or believe
• Disconnect charging lead wires from vehicle alternator. This means all of them
• Run a huge wire from alternator to an ACCESSIBLE Circuit Breaker rated 200% of rated alternator output amperes
• From this breaker continue to HOUSE batteries, same gauge wire
• With a 130 ampere alternator I would use FOUR GAUGE WIRE, the entire distance
• With a 270 ampere alternator TWO AUGHT wire the entire distance
• Run an equivalent gauge wire from the engine block to house battery negative
• At house battery positive use minimum 100 amp rated separator I would choose 200 amp and run the charge lead wire to the disconnected original alternator output wires.

How can wire sizes be quoted w/o knowing length of run ?
My current house batts set 12 feet from my alternator.
In my last rig 2 6'ers sat 3 feet from the alternator.
But then, if engineering calls out 2/0 wire for everything, its hard to miss,.....I guess !:R

Home Skillet wrote:
Voltage is what charges a battery, not amps.
No need for the heavy guage wire.

Look up ANY wiring chart. The longer the run, the bigger the wire needed, or the voltage WILL drop excessively. You are correct on needing the voltage. But, that is why you need large wire.

I had a 64 Airstream 26' with the battery in the back. Could never get more than a days use at the lake out of the battery.

Did EXACTLY what was stated, separate BIG, #2, dual wire to battery from engine compartment.

Now, we got 3 days out of the same battery. Finally it was getting full!

A 130A alternator is a common OEM size. I think you will find this is a "peak" rating of only a few minutes or so. It's continuous rating is about 50-60A, called a "duty cycle". Also the drive belt/pulley system is usually only designed for about that amount of torque without protest (squealing).
I have seen rebuilts with a warning label attached with "Install only on a vehicle with a fully charged battery or warrenty is void".
I have noticed if the alternator is physically small it's continuous output rating is also small. Size does matter.

dear 'So'

Mexi is our resident battery and alternator engineer

his opinions thoughts and experience are highly valued around here

many of us have learned a lot from him

and that includes me, and i consider myself a learned and experienced electronic tech in my own right

just becomes he suggests that "you could have some fun" by modifying your charging system with the field control POT

does not mean he was wrong about using heavy wire and making the house batteries primary and the chassis battery secondary for the RV/motorhome
as the house batteries see far more use and abuse than the chassis battery

BTW .. his feild mod will work and give you total manual control
not for the avg 'Joe' that wants set it and forget,
you would have to monitor it carefully or 'cook' your batteries
but it would charge faster

ktmrfs wrote:
In my case the easier solution is to install the second alternator option in my truck. everything is there except the alternator and the different serpentine belt. then I'd have a dedicated alternator I could hook up to the house batteries, put the truck in park, set the brake and engage the "high idle" circuit and let if charge away.

Agreed, that's the best approach.