Do I need a BCDC charger?

**AK83** · 2nd January 2018, 08:11 AM

Originally Posted by John_D2

....
I’ll double check the charges at idle later today

Also take note of what is running whilst the engine is idling.
Things like is aircon on, ie. is the AC thermo fan running? Is the HVAC fan on .. etc.

No point showing a slightly low idle charge voltage if there's a massive current draw on the main battery .. etc.

eg. engine idling, may net you (eg. 13.8v) at the battery, but turn lights on and rear fog lights, and AC with fan at full speed .. and you may only see 13.2v at the battery with all those electrical items running.
Other things to consider too is the condition of the battery. It may be fully charged when you see a lower reading.

My D1(lower 100 Amp alternator compared to a D2) usually gives me 14.0-14.2v on the starter battery for about 5-10mins after the first start for the day.
My drive to work is anywhere from 20mins to 60mins.
My the time I reach a point in my drive where I then hit the freeway section(about 10mins) .. that is no brakes now, and usually no accessories running .. the voltage reading can drop to 13.8v(same gauge, same pickup point .. at the battery terminals), with no power draw from any accessories.

If I hit the brakes, obviously the brake lights at 21W each, display a voltage drop at the battery .. could drop to 13.5v-13.6v. With lights on or indicators .. etc you see further voltage drops.

DiscoMick · 2nd January 2018, 10:20 AM

So back to the original post with a question. If your vehicle was idling when you got the 13.2v readings, are they readings of the state of the batteries or of the current flowing from the alternator through the vehicle's electrical system?
If they are of the batteries then they are fully charged at 13.2.
If they are of the flow from the alternator then I think you're OK, but it could be higher. What is drawing power when idling - air-con, radio etc? Does it change when you shut them off?
For example my Defender reads about 13.9-14.0 when idling.
I don't think you need a DC-DC.
Remember that a DC-DC would limit your flow to the capacity of the unit. For example, you have say an 80 amp alternator, but the DC-DC might only operate at 20-25.
If your camper has solar then it probably has a regulator limiting it to maybe 10 amps so no benefit from a DC-DC, I think.
If the current coming through your trailer plug is less than what the DC-DC might boost it to then there may be a benefit. This is the only reason I have a DC-DC in our camper, but the solar doesn't go through it, it goes directly into the camper battery.
I have an 80 watt solar on the roof rack of the Defender, but it also goes directly into the starting battery.
Hope that helps.
I'm not a technical expert so this is my non-technical explanation.

**trout1105** · 2nd January 2018, 12:14 PM

[QUOTE=John_D2;2756960]Quick summary:

Car

2 TD5 2000 model
Optima red top starting battery 1000cca (about)
Dual battery century 65ah next to the turbo with 3b&s dual cable to a 150amp Anderson on the towbar.
130ah dry cell battery in the camper.

No voltage drop between the dual battery & the camper (3b&s to the camper battery also)

If you have NO voltage drop between the truck and the camper batteries then I don't think you need any sort of special charger regardless of type or brand

I do recommend however that your cable from the front of the truck to the rear Anderson plug is fused at "Both" ends though.
I have been running a similar setup for nearly 3 years on my D2a with a cable running from the cranking battery (I don't have a dual battery setup) to a rear Anderson plug and this charges up to 3x 110AH batteries and runs 2 fridges ( 1 freezer 1 fridge ) and I haven't had any dramas with flat or overcharged batteries in that time.
I do however have a small voltage drop at the rear Anderson plug but this doesn't seem to matter because at the end of the days driving ALL the batteries are fully charged.

Stick with what you have got and save your quids for diesel or something "Useful" for your truck is my opinion

**Mick_Marsh** · 2nd January 2018, 01:25 PM

[QUOTE=trout1105;2757226]

Originally Posted by John_D2

I do recommend however that your cable from the front of the truck to the rear Anderson plug is fused at "Both" ends though.

Very good idea.
I would also have a fuse on the trailer as well. Up near the battery.

16mm2 (about 6AWG) cable seems a bit big, unless you're planning to start the trailer mounted V8 on the powered trailer. 120A! What are you powering?

DiscoMick · 2nd January 2018, 01:49 PM

Yep, can't have too many fuses.

**Milton477** · 2nd January 2018, 03:59 PM

One has to remember that a fuse is there to protect the cable from releasing it's smoke in the event of an overload or short.
If you have, or potentially have, a battery on each end of the cable then you need a fuse on each end.
The fuse is generally sized to suit the maximum current that the cable can safely carry or smaller.

**John_D4** · 2nd January 2018, 04:03 PM

My bad, fuses were an assumed part of the discussion. I have 1x 80amp at the dual end of the 3b&s and another 80amp at the camper battery. I thought this would be sufficient.

**John_D4** · 2nd January 2018, 04:04 PM

[QUOTE=Mick_Marsh;2757255]

Originally Posted by trout1105

Very good idea.
I would also have a fuse on the trailer as well. Up near the battery.

16mm2 (about 6AWG) cable seems a bit big, unless you're planning to start the trailer mounted V8 on the powered trailer. 120A! What are you powering?

It’s 3b&s which is 25mm2!! Planning on running a v12 turbo diesel camping generator...anyone want to come camping with me?!!

**Milton477** · 2nd January 2018, 04:05 PM

Originally Posted by John_D2

My bad, fuses were an assumed part of the discussion. I have 1x 80amp at the dual end of the 3b&s and another 80amp at the camper battery. I thought this would be sufficient.

Perfect!

**John_D4** · 2nd January 2018, 04:08 PM

Also, on the tow bar I have 1x150amp Anderson plug, plus I’ve spliced in a 50amp to sit next to it to make it more universal

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