Major Battery Charging Configuration Via Vehicle Alternator

First, let me say that charging deep cycle batteries via vehicle charging system is very inefficient. And if you are using true deep cycle batteries (as opposed to vehicle starting batteries), you'll dramatically shorten their useful life.

1. Unlike vehicle starting batteries, RV deep cycle batteries are not designed to tolerate high amps - both charging and discharging. Trojan's T-105 (225Ah), for example, is rated @ 75A.

2. The vehicle's charging system is designed to briefly output high amps when it detects low voltage (discharged) conditions. As the battery voltage rises during charging, the output amperage proportionally decreases. Problem is, the vehicle charging amperage is much too high initially (typically 80-140A), then quickly drops well below the the most efficient charging amps for deep cycle batteries which is typically 25-30A continuous, but depends of course, on the battery's AH rating and ambient temperature.

MEXICOWANDERER wrote:
Wanna get exotic? Dig up a THIRTY OHM EIGHTY WATT RHEOSTAT, and wire that into the negative field shunt that you made to chassis ground. Now you are the boss, not a 29 cent chip. And NO it will not "hurt" the ECU unless you forget what you're doing and pass out in a hammock. This is FULL MANUAL CONTROL of your alternator.

With all due respect, I think this a very bad suggestion. You'd need to control both the engine RPM and field voltage. And if you inadvertently failed to closely and continuously monitor both battery voltage and amperage, you risk, at a minimum, of destroying the battery(s). 'Exotic' to me, is reliable multi-stage regulation, specifically designed for charging storage batteries from vehicle alternators.

http://www.charlesindustries.com/main/ma_alternre.html

Most vehicle alternators have integrated regulators, so tapping the field is well beyond the abilities of your typical back-yard-wrench. And of those that have tried, the vast majority end up destroying an expensive alternator. If that's your goal, then spring for a 555 series Leece Neville with an external regulator - easy to by-pass or remove, without dissecting the alternator.

Since I rely on few 120Vac appliances I don't typically pack around an AC generator. I do, however, pack a portable DC generator. A 7 HP Honda coupled to a Leece Neville 24V alternator. But with solar, I usually don't need it on a regular basis.

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.

It's a reman'd Alternator rated at 130 amps, feeding 2 or 3 group 27's rated at 115 A/h each. I see that this same case alternator is rated anywhere from 60 to 120 amps. I specifically remember Kragen listing it as a 130 amp alternator when I got it in '04, and its many free life time warranty replacements from '04 to '07 when It seems I finally lucked into a good one.


The third battery is the ( 7 year old) engine battery and almost never sees any depletion besides the starter. I use a manual switch to control decide where the amps flow to/from. Circuit wise, the engine starting battery is furthest away from the alternator, even with my circuit breaker on the doubled 4 awg tripped.

Honestly I've given up on doing anything more to increase output from the alternator. The batteries seem to enjoy whatever blasting quench I, or the voltage regulator in the computer, allow them. I don't really drive very much anyway, and Solar is my main recharging source.

Removing the nearly fully charged engine battery from the alternator circuit does allow 14.5 to be held for longer, usually.

When the alternator is hot, all bets are off. At hot idle( ~ 550 engine rpm), it can't keep up with the lights and blower motor on high.

I have added a heat shield between it and the exhaust manifold, a few CM away. This was good for 5 hot Idle speed amps. I have the parts to make a cold air feed tube to its backside, but .......

Missing from the formula señor is the amperage rating of your alternator and the ampere hours of your battery bank. You COULD if you wish to get into this is to SHUNT part of the field negative from your alternator to negative. Yep the check engine light may come on. notice I said PART not all. Newer system use type A field control (called N by marine electrical types) this means the ECU throttles the NEGATIVE. The positive to the alternator field is total uncontrolled (except by the ignition switch) 12 volt positive.

Wanna get exotic? Dig up a THIRTY OHM EIGHTY WATT RHEOSTAT, and wire that into the negative field shunt that you made to chassis ground. Now you are the boss, not a 29 cent chip. And NO it will not "hurt" the ECU unless you forget what you're doing and pass out in a hammock. This is FULL MANUAL CONTROL of your alternator. If the engine bucks and farts when and if it goes into open loop because you are bypassing all those carefully manufactured insane-asylum grade software setpoints in the ECU so-be-it. It'll get over it. If a mechanic screams NO NO NO, ask him "What happens WHEN the alternator brushes wear out and the field goes to ground?" Oh I get it the alternator catches fire, the rig torches and this happens all the time, right. Look at all those flamed hulks pushed off the side of the road.

I have a direct feed from alternator to house battery with a circuit breaker on it. Doubled 4 awg wire. This is in addition to the original OEM charging circuit which has a short length of fusible link protecting it. This link can get very warm, very quickly when house batteries are depleted.


If I Manually trip the circuit breaker the max I will is about 55 amps, when cold, and this tapers quickly as the fusible link warms. If I bring in the doubled 4 awg feed to the depleted house batteries, the current to the batteries doubles with sufficient engine rpm and will start the single V belt squealing in protest.

My biggest limiting factor is my voltage regulator located in my engine computer. It will decide willy nilly when to allow no more than 13.7 volts. While 40+ amps might have been needed to hold 14.5, just 13 amps could be needed to hold 13.7.

A 500 amp alternator and 4/0 wire would charge my batteries no quicker when all that is allowed is 13.7

For temporary work use a stud (with protective cover) mounted on a fender well.

Use a clamp on meter a DC ammeter to verify the following...

Run a four gauge wire directly to to alternator output stud.

Using at least four gauge battery jumper cables, jump a low battery from your battery to whatever bank of batteries you want to just like you've always done...

Then disconnect and reconnect the battery positive to that new stud.

S-U-R-P-R-I-S-E

Time is money when burning crude oil speculator smiles.

No, this don't work too cool on a slightly discharged battery.

I'll take a chance (but it's a loaded bet) that I burn ONE-THIRD to ONE-FIFTH the fuel you do to recharge batteries, by generator or alternator. Made of money? Then this subject is of no interest to you.

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.

Although probably impracticle for most but you would sure get the job done well with that configuration for sure.jb

One time when I let a cheapo house group 24 drop to 10v, I used heavy (4ga) jumper cables from my idling truck to charge it for about a half hour. I was surprised how well it worked.

My truck has a 220a alternator, which likely has about 130a output at idle (Ford publishes a chart showing RPM vs amps). So I may have dumped a couple dozen amp-hours back into the house battery. All I need the battery for is the fridge and detectors, so for me, enough.

All fine and good... and I have never been in such a hurry to charge by alternator.

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

RESISTANCE of the wire over DISTANCE REDUCES the available VOLTAGE at the OTHER END of said wire.

This in turn REDUCES the available AMPS that the devices on the other end of said wire gets.

When working with low voltages like 12V you MUST UPSIZE the wire as much as possible in order to REDUCE the resistance (IE voltage lost in that resistance).

With 12V wiring even .1V is a HUGE LOSS since the usable voltage of a 12V battery system ranges from low of 10.5V (fully flat battery) to 13.2 for a fully charged battery at rest. Basically a voltage range of 2.7V!

You simply can not use the rule of thumb for 120/240V devices which is 5% voltage loss allowable in a 12V system.

For 120V a loss of 5% is 6V so 120V would be 114V which is acceptable.

For 12V systems the battery voltage at rest is typically 13.2 so 5% loss is .66V giving you 12.54V or only 2.04V from a flat battery voltage...

When it comes to charging batteries quickly any unnecessary RESISTANCE in the wire is a bad thing and not wanted...

Mexico is on the right track...