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U1300 L ambulance 1990
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Discussion Starter · #1 ·
Situation: 24v system, two (2) independent alternators and external regulators. One for the vehicle, one for the camper. Vehicle alternator not charging. Here’s what we’ve done.

We have checked the earthing cable under the gear case and found it to be properly connected both mechanically and electrically.

Next we checked the DF connection for continuity between the alternator and the regulator and this is also good.

We have proved by a process of elimination that both alternators and regulators are functional when installed in the “camper/house” position. Conversely neither Alternator/regulator pair produces any output when installed on the truck circuit???

We checked continuity between alternator and regulator on the D-, D+, DF and D- continuity to ground. All circuits were found to be as expected. We see Battery voltage on D+ at the alternator on the truck side. We also disconnected the Alternator W wire feeding the Tach to ensure that it was not creating an issue and found no change.

As a further test we checked all circuits for connection to ground and found that on the truck side there is a connection to ground on the D+ circuit at 35 Ohms with the dash light in the circuit and 316 Ohms with the dash light removed. This condition is not present on the Camper circuit. With the diode block and the light bulb in the dash removed we still see a 316 Ohm connection to ground.

We checked Voltages on the regulator with the truck running on the house side as follows:
D to D+ = 28.29V (Battery Voltage)
D- to DF = 2.4V

On the truck side again with engine running we see....
D to D+ = .087V
D- to DF = 0V

Diodes V1, V2 and V3 were tested and found to be OK.

At this point, our assessment is that something is preventing D+ at the regulator from seeing Battery voltage. Ergo because of an absence of battery voltage on D+ there is no charging due to an absence of an energised field.

Given the foregoing your thoughts and insight would be most appreciated.
 

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1981 Unimog U1300L - ex German Military
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Are you able to post a simplified diagram as to how you have connected them. I don’t know what you mean by D, D+, D-, DF etc.

I’m my U1300L I have a single alternator but a battery to battery charger for the camper batteries which always ensures the truck batteries are charged up first.

Dan.


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U1300 L ambulance 1990
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Discussion Starter · #3 ·
Diagram not available. I'm not familiar with auto electrics but have two knowledgeable guys helping me out.
 

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Ottersburn - The terminals on an alternator very from model to model but as I know it they are usually described described something like:
D+ - Positive voltage from charge lamp (one side connected to battery) to alternator. When the alternator is not outputting the voltage on the alternator D+ pin drops and the charge lamp turns on.
DF - Field voltage, regulator output to rotor coil. The amount of voltage/current on this pin causes the alternator/generator to output more or less power. (The presence of this would seem to indicate the regulator is separate from the generator).
D- - Negative voltage reference for the DF.
D - I have no idea... ground reference for charge lamp or main ground??? Looking at a Bosch alternator cross-reference sheet, some Hitachi/Mitsubishi/Nippon alternator have this pin and Bosch marks it as "not used".

Then you can also have many others:
B+- Main battery output.
W - AC voltage output (pre rectifier) for tachometer.
I/IGN - Ignition (battery voltage for built-in regulator).
etc...

Basil - Since you have a DF pin, that would seem to indicate you have a regulator separate from the alternator (I think that really makes it a generator and regulator pair), correct? (EDIT: just re-read the first post and yes an external regulator). The regulator should have an input pin "61" or "IGN" that gets 24V when the ignition key is turned on (and the regulator should have a ground wire/frame). Are you getting battery voltage at the regulator 61?
 

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1981 Unimog U1300L - ex German Military
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Thanks choprboy- every day’s a school day as they say!

Basil - I only offer this as my own thought as your own setup could be very different from mine....

I considered two alternators, or preferably one single higher rated one. However, I have replaced most of the lighting with LED which dramatically reduces current draw - both on truck and camper.

We also have 200w of solar panel installed on the camper roof. The largest electric consumption by far is our fridge as we heat & cook using LPG.

We recently went on a 12 day trip around Ireland. Weather was mostly raining or cloudy - but even on cloudy days we got 30-50w. The batteries never dropped below 90% during the whole trip.

In our camper, we have 90Ah of LiFePo4 battery storage. So with a standard 55A alternator, we can completely charge the camper batteries from 0% to 100% in less than 2 hours (assuming that we’re not driving at night with headlights on).

Of course your own experience & usage will be different, but we have found the standard single 55A alternator to be more than adequate.

Dan.


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Discussion Starter · #7 ·
choprboy
Thank you. Your comment indicating that we should see 25V on pin 61 of the regulator with ignition in the run position caused us to look at that specific circuit and upon inspection we discovered that the relay K2 had come loose of its retaining bracket in such a way that pin 30 had shorted to ground through the mounting bracket and burned itself off. See photo. We pulled the relay up into its normal position, started the truck and sure enough we have a working charging system.

As such we will work out a fix to ensure that this cannot happen again and that should put an end to this particular problem.
 

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Well damn... I blindly gasped around for an answer and got it right!? Glad to hear you were able to find and fix the problem pretty quickly.
 
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