Voltage drops across the entire system

[ghost123uk]

Not a problem here, after all, electricals is my best subject, but thought it worth posting for discussion.

Voltage at the alternator output with no load (except the ignition circuit) = 14.1 Volts (new(ish) 14 Volt regulator/brush pack)
Voltage at the starter battery (under same load conditions) = 13.8 Volts.
Voltage into the split charge relay = 13.7 Volts.
Voltage out of the split charge relay = 13.6 Volts.
Voltage at the leisure battery = 13.3 Volts

Now I have double checked the condition of the main feed from the alternator, the condition of the wire (none of the "black wire" corrosion CovKid mentions) all is clean and bright. The terminals on the solenoid are equally clean and bright (it was a new starter assembly only 3 or 4 years ago).
The terminals on both batteries are clean and bright. Both batteries are less than a year old and hold a charge with no problem. Both read 12.9 Volts after a rest. The wire from the starter +ve to the relay and from the relay to the leisure is military spec (ex BR actually ) 64 Amp rated and is soldered and shrink wrapped to the relay terminals and at the battery post "ring" connectors (for maximum energy transfer = I did that just a few days ago in case the Lucar connectors and crimped "ring" connectors were dropping voltage).

As I say, no real problem here, it just shows how every bit of wire and every connection degrades the performance of the circuit (this is well known in Amateur radio circles regarding aerial connectors).

In fact, by the time you get to the fuse box, I am reading only 12.9 Volts (Good job I have the headlight relay conversion, running off the starter battery live terminal, goodness knows how low it would drop at the lamps without it )

I think I will fit a separate feed from the alternator to the split charge relay, and maybe fit a better relay too, to re-gain some of that valuable charging current to the leisure battery !

Comments invited...

[bigherb]

Where did you have the earth for the multimeter when you checked the alternator output body or engine?
To be accurate the earth needs to be at the same point although not always practicable, even the bodywork can have a surprising amount of resistance.

[ghost123uk]

Where did you have the earth for the multimeter when you checked the alternator output body or engine?
To be accurate the earth needs to be at the same point although not always practicable, even the bodywork can have a surprising amount of resistance.

Ah yes, I did check by earthing the meter to the alternator body and to a body earth. The readings were exactly the same indicating that the engine to chassis connection is fine.

I also checked for any voltage between both battery -ve's and a good body earth = they were fine (zero volts).

Tip (to others, I know bigherb will know this) = connect the +ve lead of your meter to the alternator body (or suitable bit of clean metal on the engine) and the -ve lead of the meter to a nice clean body earth (the tailgate catch bracket is good) turn your headlights on (to create a load) and take a reading. It should be virtually zero. Anything above indicates an inadequate earth from engine to chassis (front of gearbox to chassis).

[ghost123uk]

Oh, another tip. If you wish to check the actual output from the alternator there is no need to take all the draws and "stuff" out to get at the engine. If you pull the trigger wire off your split charge relay (so it has zero load on it) you can measure the real output of the alternator from the comfort of the inside of your van (that trigger wire comes directly from a separate circuit in the alternator, but one that mirrors the main output terminal).

[Oldiebut goodie]

^^^ Not if you've got a diseasal! My split charge is by the battery....in the engine bay where it should be.

[bigherb]

Tip (to others, I know bigherb will know this) = connect the +ve lead of your meter to the alternator body (or suitable bit of clean metal on the engine) and the -ve lead of the meter to a nice clean body earth (the tailgate catch bracket is good) turn your headlights on (to create a load) and take a reading. It should be virtually zero. Anything above indicates an inadequate earth from engine to chassis (front of gearbox to chassis).

Yes maximum the maximum volt drop with the engine cranking is 0.05V and 0.02V for anything else. Otherwise check for poor connections.

Oh, another tip. If you wish to check the actual output from the alternator there is no need to take all the draws and "stuff" out to get at the engine. If you pull the trigger wire off your split charge relay (so it has zero load on it) you can measure the real output of the alternator from the comfort of the inside of your van (that trigger wire comes directly from a separate circuit in the alternator, but one that mirrors the main output terminal).

Only as a guide otherwise it is bad practice if you are checking for an alternator fault as the voltage reading can be higher than the B+ alternator output terminal.

[ghost123uk]

If you pull the trigger wire off your split charge relay (so it has zero load on it) you can measure the real output of the alternator from that trigger wire

Only as a guide otherwise it is bad practice if you are checking for an alternator fault as the voltage reading can be higher than the B+ alternator output terminal.

Ah, thanks, noted (every day is a school day )

[Ian and Lins]

So is 13.8 v at the battery an acceptable reading? How much less does it have to be/go down to to be unacceptable. Not van related but asking out of motorcycle interest.

[ghost123uk]

13.8 Volts is an acceptable reading for normal use. In fact 13.8 Volts was considered the high side of normal until battery chemistry and materials changed a few years ago (not sure when ). "Just right" for a modern 12 Volt motorcycle battery I would say. Unacceptable would be anything less than 13.3 Volts imho.

"We" T25 camper owners tend to prefer a higher voltage as modern batteries can cope with it and charge up better and faster. This of course is mostly to do with getting the best out of the leisure battery. This is why one can now buy 14 Volt, or even, I believe 14.5 Volt alternator regulator / brush packs.

[California Dreamin]

The original Bosch/Beru voltage regulators fitted to our alternators had an output tollerance range of 13.8 - 14.2 volts.
Replacement aftermarket regulators tend to be set slightly higher to better suit modern battery chemistry, often with an output well above 14 volts (14 -14.5 volts)

It seems sensible, given the very long cable run on a petrol engine particularly, that the extra half volt will be beneficial.

Martin

[ghost123uk]

The original Bosch/Beru voltage regulators fitted to our alternators had an output tollerance range of 13.8 - 14.2 volts.
Replacement aftermarket regulators tend to be set slightly higher to better suit modern battery chemistry, often with an output well above 14 volts (14 -14.5 volts)

It seems sensible, given the very long cable run on a petrol engine particularly, that the extra half volt will be beneficial.

Martin

Agreed. When I bought my new regulator it was advertised as 14.5 Volt, but on testing immediately after fitting) it was only 14.1 Volts
I would like a "proper" 14.5 Volt one, (or run the lot off a Sterling charger if I could get one for around the same price )

[ghost123uk]

Just a thought, though may be a daft one = I have a half decent 500 Watt 12 Volt to Mains inverter. How about disconnecting the split charge relay from the leisure battery and using it's output to feed the inverter (so it is only on when the engine is running). Then use the mains output of that to run a modern 4 stage 20 Amp(ish) battery charger connected to the leisure battery. It might work as a poor man's version of a Sterling charger ?

[California Dreamin]

Interesting concept, I wouldn't imagine it would be very efficient and I'd be a little worried about my alternator being put under such sustained strain.
a 500 watt invertor is going to pull around 40 amps at 12 volts. Add the heated rear window/headlamp & blower motor draw to that of the invertor and the poor alternator is going to be working flat out.

A second alternator on a dedicated leisure circuit is a better idea.

Martin

[CJH]

a 500 watt invertor is going to pull around 40 amps at 12 volts.

Surely the inverter is only going to draw enough to supply the load that's connected to it. So if it's only connected to a 10A intelligent charger it'll draw a maximum of 10A (plus a bit for efficiency losses).

[bigherb]

Just a thought, though may be a daft one = I have a half decent 500 Watt 12 Volt to Mains inverter. How about disconnecting the split charge relay from the leisure battery and using it's output to feed the inverter (so it is only on when the engine is running). Then use the mains output of that to run a modern 4 stage 20 Amp(ish) battery charger connected to the leisure battery. It might work as a poor man's version of a Sterling charger ?

You shouldn't need to if the system is working correctly

Just rechecked mine.

At the alternator multimeter earth connected to the body.



At the starter battery.



And at the leisure, enough to charge the battery ok.