DC DC Chargers

Submitted: Tuesday, Aug 26, 2014 at 10:13
ThreadID: 109286 Views:2374 Replies:5 FollowUps:3
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Please be gentle I,m trying to get my very basic knowledge arround my probelm.Background Car is a Ranger xlt and I,ve had a 2rd battery put in the tub which runs 110 Waeco drinks fridge and this is connected to a DC DC charger. My understanding is Alternator charges main bat DC DC charges 2rd bat from the main all good .The main bat after 30/36 hour of just sitting drops to 11.79 volts still starts the car which Ford dealer says voltage drop with the alarms computors ect is accepable and designed to do that .
Now should the DC DC charger stop topping up 2rd bat when the ignition is off ??.
Ford say with the negative off the 2rd bat draw on the main is .002ma when connected draw on the main rises to .17ma which they claim is excessive my Auto Electy say thats not to bad .
The above voltage drop is only when the 2rd bat is being used as at the moment the 2 rd is full charged and the main is holding 12.3 v
I trust my auto elecy more than the ford dealership.
I,ve expalined it as best I can so do I have a probelm or are all makes with computors ect ect suffering from the same issue.
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Reply By: Ozhumvee - Tuesday, Aug 26, 2014 at 11:18

Tuesday, Aug 26, 2014 at 11:18
My experience with Dc to DC chargers is that they do drain the batteries (both main and auxilary) very slightly when turned off.
If the vehicle is used regularly then your drain isn't a worry. If it is left sitting for a couple of weeks then yes you may have a problem.
The vehicle I had with a DC to DC charger was left for sometimes months which led to stuffed batteries all round. The easiest solution for me was to disconnect the batteries when the truck was not used for more than a week.
AnswerID: 538189

Follow Up By: AlbyNSW - Tuesday, Aug 26, 2014 at 12:59

Tuesday, Aug 26, 2014 at 12:59
I have my DC-DC in my camper module with my second battery and it sits in the shed when not being used and yes the charger does drain the battery over time like Peter has said.

If you do leave your vehicle unused often maybe get your auto electrcian to just fit a battery switch like they use on boats etc to isolate the charger when not in use to stop the drain

FollowupID: 822518

Reply By: Wayne's 60 - Tuesday, Aug 26, 2014 at 12:37

Tuesday, Aug 26, 2014 at 12:37
Hi New Boy,

An interesting series of questions that need more information so that a correct response can be made.

WOW, a 110 ltr drinks fridge...we have the same... and a 15 ltr Engel for food. ;-}

What battery capacity do you have? IE amp hours?

What output from the alternator? Ranger XLT means not a lot to us.

What size DC-DC charger are you running?

What size battery is in the tub?

Is there a canopy over the fridge?

Are you travelling through deserts all the time?

There have been a few posts where we have posted our current specs.


Two 1000 CCA CAT batteries running off a 110 amp alternator.
One 110 ltr Waeco fridge and one 15 ltr Engel fridge.
Three x 105 amp hour batteries in the camper as a reserve to power the fridges.
We do not spend time in the bush NOT going anywhere, so our camp time is not an issue.

Don't over think what you need and enjoy your time out and about.

Wayne & Sally.

AnswerID: 538193

Reply By: olcoolone - Tuesday, Aug 26, 2014 at 13:17

Tuesday, Aug 26, 2014 at 13:17
The current Ford rangers are known to flatten the start battery quickly and over a short period and have weak battery out of the factory...... many have been replaced under warranty within 6-12 months of manufacture.

They come with a smart alternator that only charges the start battery to around 12.55 volts.

If running a DC-DC charger it is advisable to use a ignition sensing type (turns on with the ignition), if you using the REDARC ignition sensing type of DC-DC charger it will pull the start battery down to around 9 volts before disconnecting.

You can get the smart charge system turned off by Ford.

I think you mean 0.17 amps or 170ma.... not 0.17ma and yes it is acceptable in modern vehicles....... 200 series Landcruisers pull a bit more and can flatten 2 batteries within a week and a bit.

Your problem stems from the start battery not getting a charge rate as much as other vehicles and pulling 170ma.
AnswerID: 538195

Follow Up By: Slow one - Tuesday, Aug 26, 2014 at 15:06

Tuesday, Aug 26, 2014 at 15:06
As olcool says, get the smart charge disabled by Ford, they shouldn't charge anything to do it. I have a dc-dc ctek and have no problems with the smart charge disconnected.

If it is an auto PX you should get a recall letter shortly to replace the 2 auto transmission heat exchange hoses, you could ask for the smart charge to be disconnected then.
FollowupID: 822527

Reply By: Member - Frank P (NSW) - Tuesday, Aug 26, 2014 at 15:18

Tuesday, Aug 26, 2014 at 15:18
Hi New Boy

"Now should the DC DC charger stop topping up 2rd bat when the ignition is off ??."

The short answer to that is "yes".

My DC to DC charger is permanently connected to the 2nd battery. With the key off it draws a few milliamps from the second battery and NONE from the cranker.

Other designs may be different and pull a few milliamps from the cranker as well or instead of.

It should only be a few milliamps. I agree with your Ford advice - 170 milliamps appears excessive.

You could make some enquiries with your DC-DC charger manufacturer.

You could also install a solenoid that is on only when the key is on, and power the DC-DC charger from that. That way when the key is off the DC-DC would be disconnected completely from the crank battery.



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AnswerID: 538200

Follow Up By: Member - Frank P (NSW) - Tuesday, Aug 26, 2014 at 16:26

Tuesday, Aug 26, 2014 at 16:26
Maybe I didn't read your post correctly. If that 170 milliamps is drawn by the DC-DC charger, then yes, it's excessive. If it's drawn by the vehicle when you connect the cranker neg, then maybe that's the way the vehicle is designed. Seems a bit high, though, and I would not have thought it acceptable. However on that matter I will bow to those in the industry.

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FollowupID: 822531

Reply By: Allan B (Member, SunCoast) - Tuesday, Aug 26, 2014 at 16:33

Tuesday, Aug 26, 2014 at 16:33
Hi new boy,

In order to "be gentle" and assist you, we really need to know exactly what brand and what model number of dc-dc charger you have. There are various types, each with very different specifications, and without the correct information we can only guess at how yours should be performing. Otherwise, attempts to assist you may be more likely to confuse you.


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AnswerID: 538202

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