Here's one to think about, charging from the alternator

[T1 Terry]

It's all about the cable size, connections used and how well they were installed. The issue is the modern day smart alternator control that drops the alternator voltage well below the voltage most commonly experienced in the past.
We have a vehicle here common to many caravan users, a V8 Landcruiser. We fitted a 30 amp DC to DC charger in the van but it drops out every time it starts up due to low voltage. There is 13.5v available at the start battery but by the time this goes through a VSR (voltage sensing relay) 2 Anderson plugs and various connectors along the way, the voltage initially available for the DC to DC start up drops to 12.8v. When the DC to DC tries to produce 7 amps the input voltage drops to 6.5v before the DC to DC goes into error mode and shuts down. The voltage then returns to 12.8v and the whole process starts again.
The cabling between the start battery and the Anderson plug and on to the DC to DC charger is all 6 B&S (13.5mmsq) cable. The calculator http://www.calculator.net/voltage-drop- ... &x=67&y=17 tells me there should still be 11.5v under the 40 amp load required to supply the 30 amp DC to DC to put out 14v continuous, about the max voltage we would ever require for lithium batteries.
So far we haven't been able to find a poor connection that is causing the voltage drop so now it's either a case of replacing all the cable with heavier cable and the Anderson plugs so they can accept the larger cable, or boosting the voltage at the front to push more current through the existing cable.
I'm looking at adding a DC to DC charger up front to supply both the aux battery that runs the fridge in the Landcruiser and the van DC to DC charger. There is already a Redarc BCDC1225 DC to DC charging the aux battery, does anyone know if 2 of these units will run in parallel?

T1 Terry

[jon_d]

Terry,

get a voltmeter that has a min/max fast DC voltage measurement.

clip the + lead to the alternator output terminal.

clip the - lead to the DC to DC + input terminal.


Do the power on cycle and measure the peak voltage. (aka the voltage drops) This is the actual voltage drop in the + cable.

Do the same in the - cable. Add them together. .... you know the rest.

[Barboots]

Have you bridged out the VSR and tested?

Cheers, Steve

[Noggins]

Chech if the connections at the andersen plugs are crimped or soldered.
I had soldered mine initially but when things went pear shaped I fund the solder flux had corroded the cable back by about 1.5" and there was just enough connection to give voltage at static but ask it to supply any current and it just dropped the bundle.

Had to undo all the connections stretch the cable and crimp all the connections.


Ron

[Paramountcruiser]

Fit a booster diode : https://www.hkbelect.com/

[T1 Terry]

Chech if the connections at the andersen plugs are crimped or soldered.
I had soldered mine initially but when things went pear shaped I fund the solder flux had corroded the cable back by about 1.5" and there was just enough connection to give voltage at static but ask it to supply any current and it just dropped the bundle.

Had to undo all the connections stretch the cable and crimp all the connections.


Ron

Got it in one, well done to that man Turned out the auto sparky who fitted the Cruiser side of the Anderson plug pair had soldered the terminals on the cables and he was the one doing the testing for voltage drop as the vehicle had already left here. We didn't get to test the set up until the lady was about to leave and backed the Cruiser up so we could plug in the Anderson plugs.
Seems he was doing the testing no load, when it was suggested applying a load and do the test again the problem was there and a trace back lead to the Anderson plug negative.
Problem now solved in this case, but many vehicles are now dropping the alternator voltage to 13v once the battery voltage has been sensed at having reached 14v or even 13.6v in some cases. Not many connections required to add enough resistance over the 14mtrs or more to drop the loaded voltage far enough for the DC to DC charger to drop out due to low input voltage or severely restrict its output to maintain the input voltage at a useable level, or maybe the input current at a level safe for the unit, the latter probably being the more likely.
It certainly knocks the myth about direct alternator charging being better than DC to DC charging, if the required voltage can't be maintained once the current flow (amps) increases then not only won't the alternator charge the house battery, it won't power the fridge properly either.

T1 Terry

[Toolman]

How many times do people have to be told : Crimp, do not solder!

[Eddy]

I had soldered mine initially but when things went pear shaped I fund the solder flux had corroded the cable back by about 1.5"


Ron

Ron was the soldering done with the flux cored solder meant for copper wires ? - I would have thought the flux used in this type of solder would have been non corrosive

[T1 Terry]

How many times do people have to be told : Crimp, do not solder!

But you need a good quality hex pattern hydraulic crimper and not one of the dimple crimper pair of oversize pliers. The idea is to crush all the fine strands together till that part is almost solid copper and the crimp terminal used must be thick enough material to hold the wires crimped that tightly. The dimple crimpers just spread the fine wires out to the edges, the few actually crimped under the dimple get hot and deform reducing the tension on the bond between the lug and the cable and after a while the cable will simply pull out of the lug. I come across that problem more often than the failed solder joint. The failed solder joint is usually the result of a dry solder joiny or having the lug on the same plane as the cable or even slightly up hill. The solder then runs down inside the cable insulation rather than into the joint and a dry joint results. Poor connection then creates heat melting the solder again and the whole lot runs out of the lug and up into the cable leaving nothing but tinned cable floating around inside the lug. If you must solder the joint, put the lug between 2 pieces of board in a vice, heat the lug and melt the solder into it and while still applying the heat, push the cable into the solder pool. This way the solder will not run back up the cable and you know for sure it bonded with the lug.

T1 Terry