Test with DCDC/VSR and Camper trailer.

[SimpleSi Member Find all posts View Profile Close SimpleSi]

I wanted to reconfigure my electrics to maximise charging to my camper trailer batteries for an upcoming trip.

The gear:
2010 Prado GXL 3.0D4D. Starting battery is a new Optima Redtop D34R. Aux is a 55aH Optima Yellow-top D34.
Camel Camper Trailer has 2 x 105aH AGM batteries.

A Few months ago the alternator in the Prado died, so (just in case) I removed LeighW's voltage booster, and installed a CTEK D250S DCDC charger between the Start and Aux batteries, and obviously replace the alternator to Toyotas upgraded alternator.

Before my testing today, I ran down all the batteries a bit. This isn't an ideal "Resting voltages" test, but the numbers were:
Start batt 12.35V
Aux batt 12.5V
Trailer batt 12.35
Testing equip is standard voltmeter and clamp-type ammeter

So, current setup:
DCDC charger to Aux, and the anderson on the towbar runs off the Aux battery. Basically the 20A D250S is charging 265aH of batteries. Probably not ideal.



Results: (after starting the car)
Start batt 13.46
Aux batt 13.1V (and rising. I think it was in the Bulk phase with voltage steadily rising)
Trailer batt 12.6V (and rising as per above)
Amps to Aux batt 19.8A
Amps to Trailer batt 6.5A

I then replaced the ALT-S fuse with Leigh W's voltage booster, however I installed it the wrong way around, and surprisingly enough, the results were the same! (ie I buggered this part of the test)

[SimpleSi Member Find all posts View Profile Close SimpleSi]

I then removed the DCDC charger, and installed a Projecta 150A VSR in between the Starting and Aux batteries.



results were as follows. (Without voltage booster fuse/with voltage booster fuse)

Start batt 13.53V/14.01V
Aux batt 13.36V/13.82V
Trailer batt 12.85V/13.0V
Amps to Aux batt 25.5A/37A
Amps to trailer batt 9.6A/14A

[SimpleSi Member Find all posts View Profile Close SimpleSi]

Final step (and what will be the final setup)

VSR between the car batteries, and CTEK D250S installed in the Camper trailer



Results (without voltage booster fuse/with voltage booster fuse)

Start batt 13.54V/14.1V
Aux batt 13.41V/13.9V
Trailer batts 13.0V/13.12V (possibly increasing voltage as per bulk phase)
Amps to Aux batt 28A/41.5A
Amps to trailer batts 14.1A/19.6A

I was surprised at the difference in current the voltage booster seemed to make between the start battery and Aux.

The one thing this doesn't prove is the age old question of can you fully charge an aux battery via VSR. Given my normal short trip driving style, I intend to throw the 15A 240V charger on the car batteries every few weeks.
So my plan is keep the the DCDC charger in the trailer, and keep LeighW's voltage booster in. Plenty of amps to the Aux battery and 20amps/hr of driving into the trailer batteries. I'll also install my Victron 15A MPPT Solar regulator on the start battery. 80W solar panel will soon be permanently mounted on the roof. Should be GTG!

Hope some useful info for others.

[GEEEXL Member Find all posts View Profile Close GEEEXL]

geeze another alternator gone with a booster aye

[hulbyw Senior Member Find all posts View Profile Close hulbyw]

I have a DC/Dc charger in my Prado to charge the auxilliary battery. I am taking delivery of a new camper tomorrow and it has a DC/DC charger. My previous CT did not.

I have been told to change my Anderson plug source power from the auxillary battery to the starter battery now that I will have a DC/Dc in the CT.
Cheers

[SimpleSi Member Find all posts View Profile Close SimpleSi]

Sounds reasonable. Unfortunately my 12v sockets in the boot (fridge) is connected to the towbar anderson plug, so it needs to be connected to the aux battery.
@GEEEXL A mate with a booster also had his alternator die at about 100,000km. RACQ dude said he sees many Prado alternators cark it at about that stage. Perhaps just a weak alternator...

[sweetpea Senior Member Find all posts View Profile Close sweetpea]

I then removed the DCDC charger, and installed a Projecta 150A VSR in between the Starting and Aux batteries.



results were as follows. (Without voltage booster fuse/with voltage booster fuse)

Start batt 13.53V/14.01V
Aux batt 13.36V/13.82V
Trailer batt 12.85V/13.0V
Amps to Aux batt 25.5A/37A
Amps to trailer batt 9.6A/14A

In all three examples the picture shows that the cable that goes to the AUX battery also supplies the current to the trailer.
This would mean the

Amps to Aux batt 25.5A/37A

also includes the

Amps to trailer batt 9.6A/14A

Or have you measured only the current going into the AUX battery?

Thanks,

S.

[SimpleSi Member Find all posts View Profile Close SimpleSi]

In all three examples the picture shows that the cable that goes to the AUX battery also supplies the current to the trailer.
This would mean the

Amps to Aux batt 25.5A/37A

also includes the

Amps to trailer batt 9.6A/14A

Or have you measured only the current going into the AUX battery?

Thanks,

S.

Yes, amps to the trailer is downstream of the "amps to aux". So in that case, (with the voltage booster in) 23amps is remaining in the battery, and 14a are going to the trailer (considering no loss).

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi S and there are two relevant factors not show in your data.

Neither Cable size or cable length are shown, but from the voltage drop to your trailer batteries, I would GUESSTIMATE the cabling is no bigger than 8B&S ( 7.9mm2 ).

With 6B&S cabling, I would have expected 30+ amps at the two trailer batteries.

[SimpleSi Member Find all posts View Profile Close SimpleSi]

You're right Drivesafe, it's a hodge-podge of wiring.
I've got 4B&S between start and Aux batteries (but still seeing voltage drop???)
I believe it's 6B&S from the RHS Aux, all the way back around the LHS (past the Start batt) to the Anderson plug. Trailer wiring looks like 8B&S AT BEST. No time to replace the trailer wiring, I think it will suffice for my upcoming 4 week trip (Bris-Darwin-Bris) in 2 weeks. The run from the Aux battery to the Anderson plug at rear is also longer than it should be.
Simon

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

geeze another alternator gone with a booster aye

Luck of the draw, many more without boosters fitted would die than those with boosters, alternators wear out as they are treated a non serviceable item. Personally I would pull the alternator out and service it myself at 100000Km, with the Prado most failures seem to be the brushes (jammed up with mud) or the clutch goes. Modern alternators work harder than old types, amps have gone from 30A up to 100A - 130A being common, and more crowded engine bays with more powerful engines result in higher temperatures.

The simple fact most miss, is the booster causes very little extra load on the alternator, it is the extra batteries that are increasing the load!

If an alternator is rated at its maximum power at 13.5V for instance [email protected] volts or 1215W it can still only produce 1215W with the booster fitted.

Even if we ignore the above, if a 100A alternator is running at 100% output at 13.5V the load resistance would be .135 ohms. If we increase the system voltage to 14V the current becomes approximately 103.7A or 3.7% increase!

The booster simply trades reserve current for a voltage increase, once the alternator output gets up around the 90% load mark there won't be any real difference between the alternators output voltage or current with or without a booster fitted. Connect three flat batteries to your alternator, it is not going to charge at 14V with or without a booster fitted, it will be down around 12.5V and then it will rise as the surface charge on the batteries rise and their current draw decreases. The booster will allow higher battery charge voltages when reserve current is available ie as the load on the alternator starts to reduce the system voltage will rise to till it reaches the regulation voltage, without a booster it might be 13.5V it will stop rising at this point and the current flow will start to reduce. With a booster fitted it might rise to 14V.

You can if you wish use a DCDC charger to limit the current and still provide a higher charge voltage at the end of the batteries charge cycle this would limit the current to a maximum of say 20A in the case of a 20A charger. The issue then becomes recharge times, if we have a 100Ah aux in the car, and two 100Ah in the trailer discharged to 30% SOC it is going to take 12 - 13 hours drive time to recharge them, is this practical? You could use a 40A charger to reduce the recharge times but then your current load on the alternator will be getting similar to a VSR setup.

Another alternative to limit the current would be a length of suitable cable, this would restrict the current when the battery is low, generally though 99% aren't complaining of excess current and to fast recharge times.

Another option, less battery capacity!

Simple fact is if you believe your battery load is large enough to be killing your alternator and you want reasonable recharge times the only real option is a higher output alternator.

[sweetpea Senior Member Find all posts View Profile Close sweetpea]

The simple fact most miss, is the booster causes very little extra load on the alternator, it is the extra batteries that are increasing the load!

If an alternator is rated at its maximum power at 13.5V for instance [email protected] volts or 1215W it can still only produce 1215W with the booster fitted.

Morning Leigh,

I agree with all of what you said and that the additional load on the alternator due to the diode is trivial.

However I have a question about the above quote and it is easier to ask here than go look it up.

The last time I looked at the function of automotive alternators was about 3 or 4 decades ago so I may be well out of date. I seem to recall that alternators were inherently current self limiting. Hence the output of an alternator was limited by a maximum current and regulated for voltage.

Back then alternators were rated at a maximum current and without a rewind you could not increase that output current.

If that is still the case and the current maximum remains constant the Watts produced will increase with increased voltage at that current.

If the diode increases the maximum voltage by 0.6 V then the output power in your example would be 90A X 14.1V = 1269W which is a trivial increase and full output power, either with or without a diode, will most likely never be achieved in the real world due to cable resistance and the internal resistance of the batteries.

If modern alternators are different could you please point me to a suitable reference so I can update my knowledge.

Thanks,

S.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Its not so much that alternators have changed its the way they rate them, the its power they now generate and environmental factors. Their putting out 4 to 5 times or more the power they did 30 years ago, and they are generally smaller.

A quality alternator will be rated at 25C, it will have access to unlimited free air flow so that it
can shed its heat load, this is not likely to be the case when the alternator is installed in an engine bay.

One manufactures has indicated they rate their alternators after a settling time for the internals to reach a predetermined temperature but before they reach their peak temperature?

One manufactures has indicated their alternators can run at 100 output continuously providing the alternator can shed its heat load, others indicate that except in the case where the alternator has been designed to run at 100% output for extended lengths of time all their alternators should be derated by around 20% - 30% for continuous high loads..

Basically its not that your drawing excessive current, its more about the alternators ability to get rid of the heat its it's generating, you may only being drawing 70% of its rated power but if it can't shed its heat load and the rectifiers over heat that's that.

Modern temperature compensated alternators will self protect to some degree as a result of their regulators being generally located at the back of the alternator, hence if the alternator starts to heat up it will see this as a rise in ambient temperature and lower its output. This shouldn't be relied upon as a fail safe though as that's not what it was designed for.

I charge 4 batteries off my Prado's alternator and haven't had any issues with the alternator, I know of others who charge 600Ah of batteries, it really gets down to the simple fact the batteries have to be charged and the power has to come form the alternator. Charging an extra aux in car with a VSR or 40A charger will put about the same extra load on the alternator. Adding another two batteries in a trailer for example is really going to increase the load that much due to cable length and the car aux pulling the voltage down till its charge rate drops. adding extra batteries will of course increase the time period the alternator has to generate higher current for but doesn't matter what systems you use to charge the batteries the power still comes from the alternator. If you wish to limit it to say 20A then a DCDC might be the solution, in my case I need to put back 200Ah back in to the batteries in a 4 - 5 hour drive time a 20A charger is not going to cut it, till recently I was using a combination of a marine pro and gel batteries, now have the marine pro and Lithiums in the van, to that end I have a 30A DCDC in the van, I need the charger as the Lithiums have a much higher terminal voltage ie 13.3V when considered flat. The aux in the car is charged via a VSR and booster diode setup.

I get around 20A into the 200Ah Lithiums when their down to 30% SOC without the charger and I could have rewired the car to increase that but due to the charging requirements of the Lithiums decided the DCDC charger was the go as it can be programmed to stop charging once the Lithiums are charged. The booster also provides a higher input voltage to the DCDC charger and makes it more efficient.