dc/dc chargers

Submitted: Friday, Apr 29, 2016 at 16:03
ThreadID: 132266 Views:2828 Replies:10 FollowUps:22
This Thread has been Archived
Please advise me about dc/dc chargers. When travelling I run my fridge on 12 volt via Anderson plug. At the end of day I normally have about 12.7 volt left in the 2
batteries. so what I need is something helping charging when on the road.
Is the dc/dc charger to be fitted in the car or in the van?
What size charger should I choose? and what brand?

Thanks for your help
Jorgen

erik

Lifetime Member
My Profile  My Blog  My Position  Send Message

Back Expand Un-Read 0 Moderator

Reply By: Frank P (NSW) - Friday, Apr 29, 2016 at 16:33

Friday, Apr 29, 2016 at 16:33
Hi Jorgen,

What sort of fridge do you have and do you know what current it draws when running? This will help people provide an answer.

Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

AnswerID: 599324

Reply By: Member - Jorgen S (QLD) - Friday, Apr 29, 2016 at 16:46

Friday, Apr 29, 2016 at 16:46
It is a Dometic 220 l drawing around 17 amp
erik

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 599326

Follow Up By: Frank P (NSW) - Friday, Apr 29, 2016 at 17:31

Friday, Apr 29, 2016 at 17:31
Jorgen,

12.7 volts is pretty much a fully charged battery. From the info you've given us we cannot really work out what your electrical system is, so is there really a problem?.

If you need more charge in your van batteries, you won't get the best results from a dc-dc charger if the battery you're trying to charge has a 17 amp load on it.

The best solution is to have an isolator in the car and a change-over relay and a dc-dc charger fitted in the van.

This is what I would do if I were you:

1) If you haven't done it already, install an isolator in your car so that power goes from your car to the van ONLY when the engine is running.

2) Cabling from the engine battery to the isolator and then to the Anderson should be 6 gauge. Cabling from the caravan Anderson to the distribution point in the van should also be 6 gauge.

3) Install a change-over relay in the van so that the fridge is powered from the car while the engine is running and from the van battery while parked (until you switch over to gas or 240).

4) With this heavy cabling, if your car alternator puts out about 14.2 to 14.4 volts measured at the van's electrical distribution point with the fridge running from the car on 12 volt, you may not need a dc-dc charger. This is highly unlikely. Therefore,

5) Install a dc-dc charger in the van. Amp output will depend on battery type. 20 amp will probably be safe for two batteries in parallel, but that's a bit of a guess as I don't know what batteries you have. Two 100 amp-hour deep cycle AGM batteries in parallel should be ok with 20 amps going into them. Some brands can take a lot more, so more info required if you want more specific advice.

Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

2
FollowupID: 868554

Reply By: Member - tazbaz - Friday, Apr 29, 2016 at 16:55

Friday, Apr 29, 2016 at 16:55
You will need a DC to DC charger located in the van as near as possible to the van battery/s. Redarc has good information: https://www.redarc.com.au/images/uploads/images/Redarc_BCDC1240_40A_in-vehicle_battery_charger_130408.pdf
AnswerID: 599327

Reply By: Member - Boobook - Friday, Apr 29, 2016 at 19:59

Friday, Apr 29, 2016 at 19:59
If you have 12.7V in the batteries while the engine isn't running then I would say all is working 100% perfectly.

12.8V unloaded is fully charged.

DC to DC converters are more marketing than reality.
I think you need to tell us more before anyone can make an informed response.
AnswerID: 599334

Follow Up By: vk1dx - Saturday, May 07, 2016 at 08:02

Saturday, May 07, 2016 at 08:02
Quite true mate. We just have a Redarc 200 amp isolator between the batteries and all runs perfectly. When the motor is switched off the isolator opens the connection between the crank and the 2nd battery, which is actually two more batteries in parallel that we call the accessory battery. This means that the crank doesn't get flat running the stuff connected to the accessory battery. Accessories include two Engel batteries, driving and fog lights, camp lights and anything connected to the extra 12V outlets located around the car.

I took the local Redarc sellers advice to just get an isolator and all works like a dream.

Phil
0
FollowupID: 868905

Follow Up By: Member - Boobook - Saturday, May 07, 2016 at 08:35

Saturday, May 07, 2016 at 08:35
Actually Phil, a DC - DC converter to charge a second battery under the bonnet or in the vehicle is actually a huge negative compared to a 200A isolator.

Can you jump start from your second battery if you have a dead main one? NO.
Can you join both batteries while winching? NO.
Are the electronics totally sealed? NO.
Does the Auto elec or retailer make more money? YES.


I bought a 40A DC to DC charger for my camper. I already had 3B&S cable to the rear of the car, and 8 in the camper. The charge time, even at idle was at least 20 % longer with the DC - DC installed.

Go figure!!! It's sitting in the garage with all my other junk now.

After struggling to find the best solution for years. I think the following is the best for rapid, reliable charging.

1)200A isolator with 2B&S cables and an over-ride switch for jumping.
2)As heavy as possible cable to the rear andersons and in the camper.4 or bigger.

3)a diode booster. BUT only use it when touring. I think it does reduce battery life of the main batteries if left in all the time.
0
FollowupID: 868906

Follow Up By: vk1dx - Saturday, May 07, 2016 at 09:03

Saturday, May 07, 2016 at 09:03
We have the SBI212 and the answers to all the above are YES. We can bring all three batteries together for starting and winching.

I should have mentioned the model number in my first post but I couldn't remember it.

Sri

What is a diode booster? If it a bank of charged up electrolytic capacitors? I used them decades back to change point motors on my train layout. Not in favour of them. They can dry out and lose their charge if not "cycled".

Phil
0
FollowupID: 868909

Follow Up By: Allan B (Member, SunCoast) - Saturday, May 07, 2016 at 09:36

Saturday, May 07, 2016 at 09:36
.
Phil, a so-called "Diode Booster" is a simple diode placed in the voltage-sensing wire to the alternator. It introduces about 0.5v drop in the circuit and fools the alternator into thinking that the battery voltage is 0.5v lower than it really is thus causing the battery to be charged to 0.5v higher higher than the alternator regulator was designed. It is marketed as a diode contained within a fuse body for ease in inserting in the circuit.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 868912

Follow Up By: vk1dx - Saturday, May 07, 2016 at 09:41

Saturday, May 07, 2016 at 09:41
Thanks Allan. I have since out what they were.

Still don't like them. The windings would be selected for a certain current. Upping that current could do lots or nothing. Personally I would change the alternator to a bigger one.

The autoelec that we use mentioned them and said it would be better all round to put a bigger alternator on the car. Don't forget mate, that we maintain the car to "bring us home". Not to just get there etc.

Phil
0
FollowupID: 868913

Follow Up By: Member - Boobook - Saturday, May 07, 2016 at 11:46

Saturday, May 07, 2016 at 11:46
Phil
HKB sells them and can supply a lot more info on how they work and their effects.

I am very satisfied that they will not harm the alternator in any way whatsoever ( in a 200 anyway which has a 180 Amp alternator).

My only issue with them has been that I believe the higher voltage has shortened the battery life in the past ( though I must admit that i seem to be alone in that view). So I take it out unless actually using the aux and camper batteries on trips. I'm happy with that. Also I have never used HKB's brand.

I think they are only of use in recent vehicles that deliberately make the alternator output very low in order to improve emissions and economy by a bee's dick.
0
FollowupID: 868918

Follow Up By: vk1dx - Saturday, May 07, 2016 at 12:19

Saturday, May 07, 2016 at 12:19
It may shorten their life. Good point. I am surprised that with a 180 amp alternator that you really need it.

Work to do here before our next trip. Apart from gardening there is a rattle in the car that I would like to get rid of. Rattles = something loose = who knows!!

Catchya

Phil
0
FollowupID: 868919

Follow Up By: Allan B (Member, SunCoast) - Saturday, May 07, 2016 at 14:49

Saturday, May 07, 2016 at 14:49
-
Sorry Boobook, I must disagree with your comments re dc-dc chargers compared to simple isolators. They both have their merits but it is wrong to describe a dc-dc charger as a "huge negative".

The standard automotive alternator is basically a simple fixed-voltage charger. It maintains a fixed output voltage throughout the charging cycle. This is not unreasonable for charging flooded lead-acid cranking batteries where they are discharged very little during an engine start procedure and the recharge lasts for only a few minutes but is less than ideal for replenishing well discharged deep-cycle batteries. This "fixed output voltage" may be modified in magnitude by modern Engine Management Systems to satisfy emission considerations but still remains as a fixed-voltage charger.

On the other hand, dc-dc chargers invariably incorporate an algorithm that provides multi-stage charging which is acknowledged as being appropriate for deep-cycle batteries, particularly AGM type. They also have the benefit of limiting the charge current to a value nominated by the battery manufacturer. An additional advantage is that this bulk-charge current can be maintained throughout that phase whereas a constant-voltage charge will diminish as the battery voltage rises.

Certainly, direct alternator charging may bang the joules into the auxiliary battery rapidly, but is this good for your battery?

To address your 4-points of question:
Can you jump start.......? Yes, I have a 200A solenoid which can connect my Aux Battery with the cranker.
Can you join batteries for winching? Yes, same as above.
Are the electronics sealed? No, they don't need to be. My dc-dc's are in the cab.
Does the retailer make more money? A very good question indeed. The commercial "Diode Boosters" are comprised of components costing less than 50 cents yet are marketed at $50 each. I would say "You go figure".

My two 20A dc-dc chargers maintain my auxiliary batteries well and their life appears to be extending much further than when they were connected directly to the alternator via a solenoid isolator.

Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 868925

Follow Up By: Frank P (NSW) - Saturday, May 07, 2016 at 15:52

Saturday, May 07, 2016 at 15:52
100% what Allan said, point for point.



The van setup is exactly the same as the tug's canopy setup.

It works brilliantly.

Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 868926

Follow Up By: Member - Boobook - Saturday, May 07, 2016 at 18:00

Saturday, May 07, 2016 at 18:00
Allan and Frank, I think if you make an informed decision then everyone will have different requirements. But the reason you can winch or jump start is the heavy duty isolator,in your system not the DC to DC charger. So you have installed BOTH systems. That is increased complexity and dollars. - What happens if you use the jump start without isolating the charger?? Relays galore to fix that.

I spent weeks comparing the charge rate with and without the DC to DC charger and, bugger me the system was faster without it. The most I ever saw was 45A ( into 220AH of battery capacity) BUT the DC DC charger dropped its charge rate off quicker than heavy cable alone. That is the opposite of what I expected ( which is why I bought a DC to DC charger in the first place.) It got in the way of a safe quick charge. IN MY CASE...

I am glad you are both happy, and in the case of Allan I have seen previous posts showing he 'gets it' so it seems to depend on the personal situation. I am sure Frank also has experience.

But DC to DC chargers are sold as an alternative to good solid cable and IMHO they aren't.




0
FollowupID: 868932

Follow Up By: vk1dx - Saturday, May 07, 2016 at 21:00

Saturday, May 07, 2016 at 21:00
Ouch I am getting out of here. All I know is that the batteries are in good nick. The fridges are happy (beer cold and ice blocks frozen. And I can tripple the capacity of the crank battery (all three are identical 105AH) with the toggle switch in the cabin without stuffing around with wires, jumper leads etc. It works for us.

I have a recording of a football match to watch. And I am turning this computer off so that you buggers don't stuff it up by telling me the score.

Phil
1
FollowupID: 868936

Follow Up By: Allan B (Member, SunCoast) - Saturday, May 07, 2016 at 22:11

Saturday, May 07, 2016 at 22:11
-
Actually Boobook, I have a 200A solenoid relay to connect one of my aux batteries to my cranking battery with the push of a dash button. It was redundant when I installed the dc-dc chargers so no cost. But that does NOT mean that I have installed "BOTH systems". The solenoid is not part of a charging system. Using the jump start has no implications for the chargers. No relays necessary.

My Redarc chargers maintain 20A until the aux batteries are fully charged then drop back to float mode so are charging at the battery max design current for the full period. (Actually they do drop a couple of Amps toward the end). But if your alternator is pushing 45A into 220Ah of battery (= 22.5A each) what happens when your battery reaches full charge? It surely does not suddenly drop the current to zero or a float rate. That is not the behaviour of a constant-voltage charging system.
Your discontinued dc-dc charger is not operating as I would expect and I am not surprised that you dumped it.

I agree that in my book dc-dc chargers are not an "alternative to good solid cable" but they do compensate to some degree for less than ideal cable.

But Boobook, despite all the theory and individual experiences, I would be the first one to declare that if something "works for you" then clearly IT WORKS!
And I would also declare that my way is not the only way. Experience has well taught me that.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 868939

Follow Up By: Frank P (NSW) - Saturday, May 07, 2016 at 22:51

Saturday, May 07, 2016 at 22:51
Boobook

By my reckoning I haven't really installed both systems. The smart isolator up front just switches on a power supply to everything else when the crank battery comes up to voltage, and switches off when the crank battery drops.

Paralelling the batteries for jump starting or winching is a very occasional event so the opportunities to stuff up are infrequent.

If I stuff up my routine by not isolating the dc-dc charger when paralleling batteries and fry it, I will just leave the manual isolator in the canopy selected on and let the smart isolator up front do its thing. My system would then be exactly as you describe your system - a bog standard isolator-controlled paralleling system. That would get me home so I can cry about the $$$ needed to fix my dc-dc charger :-)

I went down the dc-dc charger route in my previous vehicle which had a low output alternator. It has carried over into my new vehicle. In the intervening years my research has convinced me that the best way to get the best out of deep cycle and dual-purpose batteries is to give them a charging regime tailored to manufacturers specs. That's what my dc-dc chargers do.

But as Allan has said, the best system for a person is the one that works to their satisfaction.

It seems like we are on an equal footing there.

Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 868943

Follow Up By: Member - Boobook - Sunday, May 08, 2016 at 07:12

Sunday, May 08, 2016 at 07:12
When I said "Allan and Frank, I think if you make an informed decision then everyone will have different requirements." It came over the wrong way.
I meant that if you make an informed opinion as it appears you guys did, then any solution is ok. It's when you just put in a solution that may or may not fit your requirements.based on following the consensus advice form forums or retailers that you may have problems.

I didn't mean to imply that you two had not made an informed decision, quite the opposite. it just came out wrong.

Apologies.
0
FollowupID: 868947

Follow Up By: Allan B (Member, SunCoast) - Sunday, May 08, 2016 at 11:25

Sunday, May 08, 2016 at 11:25
.
Boobook, no worries mate, I think I understood first up. (more in the MM)

There are more ways to Kill a Cat than stuffing it's mouth full of jelly beans!!! lol

Having espoused the merits of dc-dc chargers, and there are some, I should say that I promote 'simple' systems in all things and respect yours. Particularly as it cannot be denied that it is working well for you. Part of the reason for my complex system is because my alternator runs a little high in voltage and partly because I wished to experiment. The experiment seems to be working well but I do not believe that it is the only way to achieve a good result. And as you said, it is expensive.

When not out in the Deserts I seem to fill much of my time fooling with the Troopy so undoubtedly will make further changes to the electrics. In striving for an ideal 'simple' system I look toward having auxiliary batteries which are more tolerant of charge and discharge conditions then simply charge them with a basic isolator. The difficulty is in selecting such batteries..... the suppliers are full of rhetoric and the users abound with diverse accounts of performance.... who to believe. But i am getting closer. If my current aux batteries cark it then I will have the justification to replace them with something quite different. And a 'simple' system.

Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 868963

Follow Up By: Frank P (NSW) - Sunday, May 08, 2016 at 12:02

Sunday, May 08, 2016 at 12:02
Boobook,

I didn't read any "wrong way" into your post, so no need for an apology, old mate.

And when you said

"I meant that if you make an informed opinion as it appears you guys did, then any solution is ok. It's when you just put in a solution that may or may not fit your requirements.based on following the consensus advice form forums or retailers that you may have problems",

I couldn't have said it better myself.

You have a working system, I have a working system, it's all good. Thanks for an interesting discussion. I hope the OP gets some benefit and is not too confused by all the options and opinions.

Cheers

Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

2
FollowupID: 868965

Reply By: Gronk - Friday, Apr 29, 2016 at 21:34

Friday, Apr 29, 2016 at 21:34
so what I need is something helping charging when on the road.


You already have it !! The alternator.

Without more info, you don't seem to have a problem, or the need for anything else to charge the batteries !
AnswerID: 599339

Reply By: The Bantam - Saturday, Apr 30, 2016 at 16:08

Saturday, Apr 30, 2016 at 16:08
Consider the price of a good DC charger and the unlikley improvement yoy may achieve.
Your money would be better spent replacing the three way fridge with a compressor fridge.

Ya fridge will then be drawing 3.5 to 7 amps ( depending on size) and not continuously.

cheers
AnswerID: 599369

Follow Up By: Frank P (NSW) - Saturday, Apr 30, 2016 at 17:08

Saturday, Apr 30, 2016 at 17:08
But then when he's camped up his fridge will be drawing on the batteries and then he'll need solar and all the rest of the stuff that generates 12V arguments on this forum.

If he's happy with gas for camping, 240 for CPs and 12V for travelling, all he has to do is make sure the fridge gets a solid 12 volts from the car under load and that at the same time his house batteries are getting a reasonable charge.

He may or may not need a dc-dc charger to do that. As I said, if it were me, that's what I'd do.

YMMV, of course.

Cheers
Cheers
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 868591

Follow Up By: Member - Jorgen S (QLD) - Sunday, May 01, 2016 at 16:22

Sunday, May 01, 2016 at 16:22
Last year camping at Cooper Pedy in 44 dec the vanners with 12 volt fridges couldn't get a cold beer but I could with my fridge on gas
erik

Lifetime Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 868625

Follow Up By: Gronk - Sunday, May 01, 2016 at 19:14

Sunday, May 01, 2016 at 19:14
Usually the other way round ??


Unless you run out of battery power, the comp fridge usually outperforms the gas in hot conditions.
0
FollowupID: 868640

Reply By: swampy - Sunday, May 01, 2016 at 10:55

Sunday, May 01, 2016 at 10:55
Hi
Jorgen S
spec 3 way fridge drawing 17 amps
Ending with 12.7 after driving
I suspect batteries are not fully charged .The easiest way to determine what your 100% full volts are, is to fully charge and measure after 24 hrs
If they are agm around 13.0volts
Lead acid around 12.7

Charging Lead acid/ wet flooded slow 10 % Fast 20% of ah
Charging agm slow 20 % , fast 30% of ah
Always refer to battery maker

Charge cable size is a serious performance restriction
To small can restrict amperage to the extent charge time is lengthened
[ Using to small a cable murders volt drop ] [ Can be around 1.5 volts at 5o amp charge rate ]
Tug end
13mm2 budget many install eventually install a second
16mm2 ok
25mm2 good
van end use
either 13 or 16mm2

Once these cables are installed verify for yourself the results

Only use at least a 30-40 amp dc to dc to be effective ideally a 40amp
Not only do u have to run the fridge but recharge the batteries also from your normal usage .

swamp
AnswerID: 599395

Follow Up By: Frank P (NSW) - Saturday, May 07, 2016 at 17:01

Saturday, May 07, 2016 at 17:01
[quote]Charging Lead acid/ wet flooded slow 10 % Fast 20% of ah
Charging agm slow 20 % , fast 30% of ah
Always refer to battery maker [/quote]

"Always refer to the battery maker"

Exactly.

In my previous vehicle I had a FLOODED "no maintenance" dual purpose battery. Manufacturer's max current was 10% of C20 amp-hours, which was 10 amps.

In my present vehicle I have an AGM. Manufacturer's max current is also 10% of C20 ah which is 13 amps
FrankP

Lifetime Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 868927

Reply By: Old 55 - Sunday, May 01, 2016 at 15:30

Sunday, May 01, 2016 at 15:30
Jorgen, I think our setups are similar, for some reason when my battery pack was installed by caravan manufacturer they wired the fridge through the van batteries. Installed Redarc 40 amp DC/DC charger and this puts in 14.5volts to the van batteries. I always make sure if we stop for lunch or other stays I turn off the fridge otherwise it kills the batteries over a few hours.
Not the best way but saves rewiring the tug.
My Prado only puts out 13.9 to 14 volts max so this resulted in about 13.5volts at the Van Batteries so the Dc/Dc charger boosted that to 14.5 to 14.7volts at the van. Was worth it to me.

Cheers
AnswerID: 599404

Reply By: Steve - Monday, May 02, 2016 at 19:50

Monday, May 02, 2016 at 19:50
Jorgen,

as others have previously stated, you seem pretty well set but you can boost your alternator's output with a diode booster for as little as $40:

http://www.sidewinder.com.au/page226.html

Simply a case of replacing existing fuse as instructed

Works well for me with a similar setup
AnswerID: 599444

Follow Up By: Member - Jorgen S (QLD) - Monday, May 02, 2016 at 19:59

Monday, May 02, 2016 at 19:59
Thanks Steve
That sounds exactly what I need
erik

Lifetime Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 868678

Reply By: David T6 - Saturday, May 07, 2016 at 07:10

Saturday, May 07, 2016 at 07:10
HKB electronics on here make and sell voltage diode boosters.
AnswerID: 599631

Sponsored Links

Popular Products (13)