Looking for a KISS DC-DC charger 12A output, NO solar ...

Submitted: Friday, Apr 25, 2014 at 19:21
ThreadID: 107463 Views:1659 Replies:6 FollowUps:21
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I'm hoping to locate a DC-DC charger for my auxiliary (AGM) battery. The battery manufacturer recommends a 10A charge rate, and sets the absolute max charge rate at 20A so I'd like to remain a decent margin below that to get a decent life out of it. About 12A would be comfortable.

I've looked through the Redarc and CTek range but there seems to be a hole in their offerings around that size. Note that no solar input is required, and I don't really want to be paying for that or any other bells and whistles - I believe in the KISS principle.

Is anyone aware of an existing product that might fit the above requirement?
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Reply By: HKB Electronics - Friday, Apr 25, 2014 at 19:47

Friday, Apr 25, 2014 at 19:47
Matson do a 10A unit, other option is to charge straight off the alternator and size the supply cable to keep charge current under 20A.

Cheers
Leigh

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Reply By: Peter_n_Margaret - Friday, Apr 25, 2014 at 21:28

Friday, Apr 25, 2014 at 21:28
Battery charge rate is determined by the voltage offered, not the Amps offered.
Were it otherwise, your 120A alternator would fry your crank battery the first day.

What is the distance between your crank battery and your auxiliary battery?
A decent size cable between the two might be all you need for a budget system.

Cheers,
Peter
AnswerID: 531223

Follow Up By: Zippo - Friday, Apr 25, 2014 at 21:42

Friday, Apr 25, 2014 at 21:42
Yes, as an electrical engineer I am up to speed on battery charging. What I am trying to avoid is the vehicle system exceeding the aux battery's recommended charge rate, which is always on the cards when the engine is started and the aux has been discharged significantly. I don't see using cable size as an appropriate "regulator". Also such a system would subject the aux to a higher-than-ideal float voltage (target is 13v7). A suitable DC-DC is considered the best overall solution, subject to finding one with voltage to suit the aux.
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Follow Up By: Peter_n_Margaret - Saturday, Apr 26, 2014 at 09:48

Saturday, Apr 26, 2014 at 09:48
The vehicle system will not exceed the AGMs recommended charge rate and it will happily float at the alternator maximum voltage.

Cheers,
Peter
OKA196 Motorhome
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Follow Up By: HKB Electronics - Saturday, Apr 26, 2014 at 11:09

Saturday, Apr 26, 2014 at 11:09
I wouldn't be to worried about the float voltage, if your actually using the system daily it would be unlikely you would fully charge the battery in a days driving at 10A, the 13.7V float voltage your referring to I assume is the maintenance charge voltage the charger reverts to once the battery is charged. The maintenance float level is more applicable to batteries being charged on a 24/7 basis and is unlikely to offer any real benefits to batteries being cycled daily in a typical dual battery setup.

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Follow Up By: Zippo - Saturday, Apr 26, 2014 at 11:24

Saturday, Apr 26, 2014 at 11:24
P_n_M: "The vehicle system will not exceed the AGMs recommended charge rate and it will happily float at the alternator maximum voltage."

That *may* be the case for your vehicle/system but it isn't here. When direct-connected the vehicle system DOES exceed the AGM's maximum charge rate, and certainly does exceed the recommended figure for an extended period after say a 25% discharge. Also the alternator maximum voltage (14v5 in this case) is not a "happy" float voltage for the AGM.
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Follow Up By: HKB Electronics - Saturday, Apr 26, 2014 at 11:37

Saturday, Apr 26, 2014 at 11:37
Zippo,

First off where is the AGM going to be located?

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Follow Up By: Member - happytruck - Saturday, Apr 26, 2014 at 11:50

Saturday, Apr 26, 2014 at 11:50
zippo,dc-dc chargers are best user to compensate for voltage drop over long cable runs. They are best used as close to the 2nd battery as you can. Cheqe out web, projecter dc dc charges, they have a u tube video you might look at also look for sidewinder abr dc dc charges . hope this helps.

happytruck
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Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 21:36

Saturday, Apr 26, 2014 at 21:36
"The vehicle system will not exceed the AGMs recommended charge rate and it will happily float at the alternator maximum voltage."

Just to add some real life measurements to disprove this: I had a Remco 100Ah AGM which specified an initial charge of less than 27Amps. I measured 45 amps going in when discharged to 50% capacity. That battery only lived 2 years and had an otherwise easy life. So after that I restricted the amperage to 20A with a DC-DC charger. The other to restrict amperage is to use undersize cable - it works, but not the best way to do this.
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Follow Up By: Zippo - Saturday, Apr 26, 2014 at 22:06

Saturday, Apr 26, 2014 at 22:06
Phil G, I have also measured 40-45A initial recharge when discharged to 75% SOC (i.e. only 25% discharged) and it is the whole reason behind wanting to control the recharge with a DC-DC unit. I had considered using cable resistance but that still exposes the battery to a too-high float.

At least someone appreciates where I'm coming from.
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Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 22:58

Saturday, Apr 26, 2014 at 22:58
Yep, I know where you're coming from!

I guess the problem here is that you are designing the system around your particular battery. If you were starting from scratch, you might consider an Optima as your AGM as it has no limit on the charge rate and is well charged from your alternator. That would be the simplest solution.

I think the Matson 10A or Redarc 6A chargers might be a bit frustrating - needing too much driving time to charge the battery (I'm assuming you're running a compressor fridge).

I have friends who have gone totally away from alternator charging. They fit a 200W solar panel and regulator to the roof of their canopy or caravan and that is all they have. Pretty cheap and simple these days provided your battery has enough capacity to run your accessories for 2 days without anything. And they get a decent regulated voltage, no setting up time and suits new vehicles with complex alternators. And they can still use the alternator if they had to.
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Reply By: WBS - Saturday, Apr 26, 2014 at 07:59

Saturday, Apr 26, 2014 at 07:59
I bristle every time I hear about the KISS principle, but that said, have you looked on the ABR Sidewinder site. They sell a variety of battery chargers. One may suit your requirements.
WBS
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Follow Up By: olcoolone - Saturday, Apr 26, 2014 at 17:42

Saturday, Apr 26, 2014 at 17:42
Did I tell you i'm an engineer!
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Reply By: olcoolone - Saturday, Apr 26, 2014 at 10:17

Saturday, Apr 26, 2014 at 10:17
One thing you want to consider is the load your placing on your aux battery and then calculate charge rates.

I would not go anything under 20-25 amps as Peter above has said and why there are not many DC-DC chargers under this figure.

If you go to the size you asked about (10-12 amps) it will take for ages to charge your battery....... The more you discharge a batter or the lower the state of charge for prolonged periods the more damage caused.

If like most you run a fridge expect 5-6 amps draw, even that the advertise .85 - 2 amps per hour, this is based on an average over 24 hours...... So straight away you have to try and put 20 - 48 amps back in over a short period of time, and if you don't you will cause more damage to the aux battery then you would by running a bigger DC-DC charger.

So when you are driving; the 12 amps per hour your putting back in your aux battery may in real terms only be 5 amps.

DC-DC charges are not a constant current device and the charge rates will vary accordingly to time and state of charge.

You have to remember pre DC-DC days aux batteries were seeing much higher charge rates and people got many years out of there batteries.

A battery can happily accept quite high charge rates under controlled conditions, a battery mounted in a camper or back of a vehicle may only see temps in the low 20`s to mid 30`s leaving plenty of room for more aggressive charge rates.

In this case applying the KISS principal on something you don't understand can be costly.

AnswerID: 531248

Follow Up By: Zippo - Saturday, Apr 26, 2014 at 15:57

Saturday, Apr 26, 2014 at 15:57
Sorry, couldn't let that one go through to the 'keeper.

1. I have done the measurements (NOT theoretical calculations) on the load on the aux.
2. During BULK charge, I expect that any decent DC-DC charger will be effectively a constant current source, and any tapering should not appear during that charging phase.
3. The vehicle will be operated daily. There will be no 24-hour consumption involved. During operation the load will still be connected to the aux. See #1 above.

Having spent a good bit of my career sizing and installing/maintaining battery systems varying from remote solar to huge UPS installations, I believe I have a fairly good handle on battery types and their care and feeding.

I do appreciate that all the feedback here is well-intentioned, but some is a bit off-target.
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Follow Up By: olcoolone - Saturday, Apr 26, 2014 at 17:39

Saturday, Apr 26, 2014 at 17:39
If thats what you think is right, i'll let you stay to your idea!

You should be able to do the research yourself on products as you qualifications are much greater then us simple plebs.......
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Follow Up By: Sand Man (SA) - Saturday, Apr 26, 2014 at 19:35

Saturday, Apr 26, 2014 at 19:35
Zippo,

Why did you bother to ask the forum for help if you already have all the knowledge?

Sometimes "Engineers" over complicate matters me thinks.
Bill


I'm diagonally parked in a parallel Universe!

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Follow Up By: Peter_n_Margaret - Saturday, Apr 26, 2014 at 20:20

Saturday, Apr 26, 2014 at 20:20
Clearly my 120Ah HGL Fullriver crank battery that is 5 years old now won't see out the next week? :(

Cheers,
Peter
OKA196 Motorhome
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Follow Up By: Zippo - Saturday, Apr 26, 2014 at 21:59

Saturday, Apr 26, 2014 at 21:59
What I actually asked the forum for seems to have been long overlooked. Just to refresh memories here:

"Looking for a KISS DC-DC charger 12A output, NO solar"
"I'm hoping to locate a DC-DC charger for my auxiliary (AGM) battery. About 12A would be comfortable."

and

" Is anyone aware of an existing product that might fit the above requirement?"
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Follow Up By: Zippo - Saturday, Apr 26, 2014 at 22:01

Saturday, Apr 26, 2014 at 22:01
Peter_n_Margaret posted:
Clearly my 120Ah HGL Fullriver crank battery that is 5 years old now won't see out the next week? :(

A cranking battery is a very different beast to an AGM, and they ARE designed to accept some pretty aggressive recharge. I'm not sure what your sarcasm was about.
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Follow Up By: olcoolone - Monday, Apr 28, 2014 at 09:28

Monday, Apr 28, 2014 at 09:28
I know I'm preaching to someone who knows it all and accordingly to your qualifications you should be more then capable to carry out the market research your self!.....

Now my advice to you is to speak to RedArc and ask them to do a special program for their BCDC 1220 charger.

It will cost you but first I would recommend to sit down and listen to what others are saying and also understand the algorithms and charging criteria they use in there charges..... this may change you view on how they work. but someone with your experience and qualification you would of done this in the first place..... wouldn't of you?

What one thinks or expects on how something works is usually a long way of the mark.....especially if you don't understand the product you are intending to use.



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Follow Up By: Peter_n_Margaret - Monday, Apr 28, 2014 at 11:26

Monday, Apr 28, 2014 at 11:26
The Fullriver HGL is an AGM battery designed for standby use Zippo.
If you care to read the specs you may just find that they will perform quite well as a crank battery as this one has done for 5 years.

Cheers,
Peter
OKA196 Motorhome.
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Follow Up By: olcoolone - Monday, Apr 28, 2014 at 12:55

Monday, Apr 28, 2014 at 12:55
How dare you Peter us a standby AGM for you cranking battery...... all the experts know it can't be done! LOL

Now getting to the real world, most batteries will last quite well with the abuse they get from most under charging, over charging, running them flat and heat.

We have many customers who have abused their "not for application - handle with care" batteries and have had many years of good service out of them often exceeding the manufactures life expectancy..... and then we have had some who has done every thing to the "T" and have it fail prematurely.

Arhhh only if we could all live in a perfect world and made sure everything we did or owned was done to 101%.

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Follow Up By: Zippo - Monday, Apr 28, 2014 at 15:18

Monday, Apr 28, 2014 at 15:18
P_n_M, you're the one who referred to your Fullriver as a cranking battery. And as a cranking battery it WILL be designed to take aggressive recharge. Do recall, if you will, that I am talking of a battery with a maximum recharge of 20A and recommended recharge 10A. As I stated, different beast entirely.

OC1, I appreciate that lots of batteries will withstand misuse/abuse but that isn't a guarantee and shouldn't be how you set up a system.
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Follow Up By: olcoolone - Monday, Apr 28, 2014 at 20:44

Monday, Apr 28, 2014 at 20:44
I think you will find Peter is using a Fullriver HGL series battery as a cranking battery....... you know in place of a starting battery!

And his point is it is accepting full alternator charge and it is 5 years old..... even that the specs say different.
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Reply By: Robin Miller - Saturday, Apr 26, 2014 at 14:36

Saturday, Apr 26, 2014 at 14:36
My Kiss easy solution is Kiss easy and works well but it only does 6amp max which is sort of a good thing.

I grabbed a car laptop supply from somewhere that was dissused , they put out voltages from about 13 to 19 for various laptops and usually have a rotary switch volts out setting.(Some later versions were automatic but you don't want that sort).

Think I set mine to 14 and put a resistor in series (think 1.5ohm- not that its really needed).

While it worked well these switch mode supplies generate radio noise and I don't like that so after a year or so I replaced it with just a low volts drop (0.3v) diode from main the aux and its good without the noise.

Robin Miller

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Reply By: The Bantam - Saturday, Apr 26, 2014 at 23:29

Saturday, Apr 26, 2014 at 23:29
Yeh see what we have to deal with here Zippo.

Many batteries have specified "maximum initial charge rates".....and that is exactly what they mean....there are a lot of people out there getting very poor life out of AGM because they have not properly managed the charge rate in acordabnce with manufacturers recommendations.

Some one sprouted that their AGM cranking battery was 5 years old and charged direct off an alternator.....congadulations.......its a f$#@!^n cranking battery, it will have a high " maximum initial charge rate".....I can call up specifications of two AGM batteries of the same size from the same manufacturer ( fullriver) that have VERY different "Maximum initial charge rates"..one in the order of 20 amps, the other so high its not worth worrying about.

Some may remember How often I say that generalasations about batteries are unreliable, because there is such variation available these days.....we MUST deal with specifics of individual batteries.

So back to Zippo's original question.
If the AGM you have has a maximum initail charge rate of 20 amps and you can keep the temperature under controll I would be happy with crarging it at 20 amps...as long as you knew it was 20 amps.

but back to the 12 amps.

I have seen bare board DC to DC power supply modules on ebay of various sizes.....some of them specifically intended for this purpose.
you probaly should look for one that has fixed current limiting in the 10 to 15 amp range or a variable current limit.

I have not yet got arround to purchasing & testing any of them but I have seen them from 1 amp up.

cheers
AnswerID: 531302

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