Normk
Canada's Wet Coast
Senior Member
Joined: 01/24/2010
View Profile
 Offline
|
mexbungalows posted: "People seem amazed when I report that I have built and rebuilt more than ten thousand domestic alternators with my own poor two hands."
I demand a recount! 
I hadn't seen the use of separate rectifier bridges so this was a "forehead smacker" because that is the obvious solution to charging of separate battery banks. I'm not off the the garage to walk in circles and smack myself on the forhead while chanting, "Stupid, stupid, stupid!" 
I've been servicing automotive alternators since the early 1970's when the first hit the market and am amazed not to have worked that out for myself or encountered the technique.
Thanks very much for the post!
I owe you lunch if you're in this area to collect.
|
DonMichUP
MI
New Member
Joined: 03/28/2011
View Profile
Offline
|
Again, very good points, and thank you. I'm still in the process, between working 12-14 hr days, of calculating my amps as mentioned before. My trip will cost around an estimated $4G just in fuel. And I had to dip into some, but not all, of the money that I had set aside. But I'm intent on taking this tour and WILL take it. Maybe not in a manner as I had hoped, but that too can be an adventure . In lieu of this, I may just opt for no alternator replacement or a slightly higher one of, say, 150-180, with a small Yamaha generator, and see how things go.
mexbungalows: that was WAY over my head , but I'm attempting to digest it, and I thank you for your knowledge.
pnichols: Yep, I'm in Michigan, in Michigan's Upper Peninsula ("U.P."), and I'm on the Wisconsin border. I live in Michigan, and actually work across the river in Wisconsin. You visited some great locations . If you have never been to the U.P. and plan to sometime, let me know and I'll give you some info on the area if you'd like.
|
pnichols
Santa Cruz Mountains
Senior Member
Joined: 04/26/2005
View Profile
Good Sam RV Club Member
|
'
* This post was
edited 02/09/12 09:17am by pnichols *
Phil, 2005 E450 Itasca 324V Spirit
|
melton
Glen Allen, Virginia
Full Member
Joined: 01/24/2007
View Profile
Offline
|
I built an external rectifier bank, like mexbungalows describes, with complete success about 8 years ago. I needed more DC amps, so i left my stock 80 amp alternator as is, and added a 200 amp alternator. Both feed the external rectifiers, and charge house and chassis batteries. When starting the engine after depleting the house batteries, i will let the engine idle a few minutes before easing off, to prevent belt slip on the 200 amp alternator. I wouldn't recommend it for everybody, but it works well for me.
forrest melton
Trust God, wait patiently, and watch expectantly.
|
howardwheeler
West, Texas
Senior Member
Joined: 07/23/2007
View Profile
Good Sam RV Club Member
Offline
|
If I could dive in for an opinion. It's not exactly the same as a Class C or A setup you're talking about with the batteries all in the same unit, but close. I just finished adding an extra charging circuit between my fifth wheel and F350 with factory dual alternators. I used 4 gauge in the truck from front to my newly installed bed plug and 2 gauge from the trailer plug to the battery bank. All told I have about a 30 foot run of wire. I have a residential frig on an inverter that I want to arrive after traveling with as full a charge as reasonably possible. I have finished the project and ran my battery bank down to around 50% then hooked up the truck. I have a Linklite battery monitor and it says with no load discernible I have a .3 amp phantom draw. With my truck charging only through the old 7 wire circuit, I am getting between 3 and 7 amps into the batteries (4 batteries total 500 amphours). When I switch on the new charging circuit (I ran a solenoid off my upfitter switches so I could control the auxiliary charging), my Linklite shows I am getting 40 amps into the batteries. That's great in my view, since the frig only draws 17 amps when running off the inverter. That's 17 amps DC. But I read about you guys talking about alternator tapering. I only ran my test for about 5 minutes at a battery discharge of about 50%. Am I going to see a marked dropoff when I really go down the road for 10 hours? Will it not keep up with a 17 amp drawdown?
|
|
|
pianotuna
Regina, SK, Canada
Senior Member
Joined: 12/18/2004
View Profile
Offline
|
Hi Howard,
There is only one way to find out. Let us know the results of your testing ok?
howardwheeler wrote:But I read about you guys talking about alternator tapering. I only ran my test for about 5 minutes at a battery discharge of about 50%. Am I going to see a marked dropoff when I really go down the road for 10 hours? Will it not keep up with a 17 amp drawdown?
Regards, Don
Kustom Koach Class C 28'5" 256 watts solar, 875 amp hours in two battery banks 12 volt batteries 2500 watt inverter.
|
Normk
Canada's Wet Coast
Senior Member
Joined: 01/24/2010
View Profile
Offline
|
The tapering off of charging is a normal effect due to the battery's increase in voltage. There are two main strategies for quickly charging a battery:
1) Constant current.
2) Constant voltage.
Modern "intelligent" chargers combine both stratagies.
In a constant current charging system, which was the high end of battery charging before the advent of smart chargers, the rated maximum charging current would be set on the charger which would increase or decrease voltage in order to maintain that amount of amps. into the battery. Temperature was monitored and the charging was dependent on time. We used this system for charging large storage batteries but it was very unusual in the automotive or RV fields. Over symplifying but that's the basic idea. It was really like setting a pump with a known pumping volume to filling a tank. A 100 gallon tank wold be filled in 10 minutes by a 10 gallon per minute pump. This is commonly used to fill storage tanks such as my friend's furnace oil tank located in his basement. Only problem was the driver didn't check to see that the tank had already been filled....another story.
constant voltage charging is the system in effect from an automotive alternator which (assuming the alternator's capacity exceeds demands) maintains a voltage set point of (around) 14.5 volts across the battery so the charging rate or current flow will depend on how much current can be forced through the battery by that difference in potential. Typical charging of an almost dead battery at constant voltage (normal vehicle or RV operation) will see a small current flow/low charging rate into the almost dead battery. Over time the current flow will increase to a maximum near about 3/4 charge and then begin to drop off.
The reason for the change in charging current is because the fixed voltage has to deal with different problems in pushing current through the battery. The charging voltage must overcome the resistance of the battery (series resistance) which is very high in a dead battery because the electrolyte is almost pure water which is a poor conductor = high resistance.
The other opposition to charging is that the voltage of the battery must be overcome by the charger so a 14.5 volt charger will have about 1.3 volts to overcome the series resistance of the battery. (14.5 volts minus 13.2 volts = 1.3 volts)
In a dead battery which has maybe 2 volts, the charging voltage unopposed is 12.5 volts but this must force current through high resistat water.
As for howardwheeler's fifth wheel, the quick answer would be to check the voltage drop in the vehicle to trailer batteries on both + and negative sides of the circuit. Have the fridge in operation with any other normal loads and measure the voltage applied to the trailer battery. That will show the real charging voltage from which rate of charge estimates can be made.
Voltage drop measurements of the + and negative circuits will indicate whether there is a need to improve some portion of the circuit.
Likely going too fast and too cryptic as under the gun to get moving.
|
howardwheeler
West, Texas
Senior Member
Joined: 07/23/2007
View Profile
Good Sam RV Club Member
Offline
|
I'll be checking voltage. I only checked to see the amps coming in. Unfortunately it's going to be a little while before I can actually drive somewhere for an extended time. But I'll get a voltage check this weekend.
|
BFL13
Victoria, BC
Senior Member
Joined: 02/15/2006
View Profile
|
The initial rapid tapering after five minutes or so is from the alternator temperature warming up AFAIK. There isn't time for the battery to get any increase in charge in five minutes. The initial battery voltage spike takes less than a minute so that isn't it. After the intial big drop in five minutes or so, then yes, the voltage regulation will mean normal tapering.
Whatever the intial amps, I tried it with different wires and got a variety, they will drop quite a bit in the first few minutes then steady and drop more slowly after that. Can't say if starting at 40 it will stay above 17 for how long.
I ran some tests of all that just by idling the truck in the driveway for half an hour. That is enough to get a good picture. You can also rev the engine with a weight on the pedal to see if that makes any difference. (not much with mine)
2003 Chev 2500HD ExtCab, LB, 2WD, 6.0/4.10 Gas
2003 Komfort 26FS 5er (28.5 Ft-RK-10,000lb GVWR)
|
