DC - DC Charger Vs Smart Solenoids

[ko7624 Junior Member Find all posts View Profile Close ko7624]

My two cents worth.....

I recommend running a DC/DC charger if your aux battery is a different construction to your regular battery ie toyota main(regular lead acid) and optima aux(AGM). Most of the battery companies will advise you the same. The solenoid system will still work but it may not give you the perfect charge for your aux battery and it might also reduce battery life expectancy. Personally, I run this DC/DC charger system and also have a manual by pass isolator switch when I want to run the winch and need maximum amps.

Cheers

Ken

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

Hi Ken,

I'm just curious as to what information your basing your advice on, for
instance the Optima battery was specifically developed for use by the
American military and was specifically designed to charge rapidly off a
standard alternator setup?

One of the key selling points of the Optima is that they can be charged
from 0% SOC to over 90% SOC in under an hour. For example a D27 when
connected to a 100A alternator will recharge to 90% SOC in around 35 minutes,
If you put a 20A DCDC charger into the equation for a D27 the recharge time
would blow out to over 4 hours?

Also where did you obtain the data that supports a running a different
type of battery to the cranking battery as an aux via a conventional VSR
will shorten its life, I haven't seen anything written on any battery manufactures
website that would support such a claim?

Leigh

[D4Dazz Member Find all posts View Profile Close D4Dazz]

I read what Ken has said on the redarc website. In fact I believe there is video link on there website where Pat Calinan explains it. May just be a sales pitch, but 2 different auto elecs have told mete same thing......

I must mention, I'm no expert, hence why a I started the thread in the first place.

[D4Dazz Member Find all posts View Profile Close D4Dazz]

Would love to know if there are any auto electricians on the forum who may be able to clear this up. Don't want to be shelling out the extra cash for something I may not need.

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

I read what Ken has said on the redarc website. In fact I believe there is video link on there website where Pat Calinan explains it. May just be a sales pitch, but 2 different auto elecs have told mete same thing......

I must mention, I'm no expert, hence why a I started the thread in the first place.

Intersting the charger manufacture tells you you need one, I wonder why?

A lot of this is pure sales hype, of course their going to tell you you need them,
as for Mr4x4 the whole show is one big add!

As far as the alternator is concerned, doesn't matter how many batteries you have
the alternator sees them as one big battery. Each battery will take what it needs
from the alternator, none get preferential treatment!

If you look at the charge voltage for the bulk charge stage (95% of the charging process), you will see that most DCDC chargers charge at around 14.4V, a standard alternator charges at approximately the same voltage, a boosted alternator (high temp compensated) at around 14.2V - 14.3V there all virtually the same.

The advantage with a straight alternator is it is not current limited at say 20A, the battery can take whatever wants up to the reserve capacity of the alternator, hence the quicker bulk charge especially with multiple aux batteries or batteries that can take high charge currents such as the Optimas.

Moderators, this info has been covered time and time again in a huge number of threads, do we really need yet another?

Leigh

[D4Dazz Member Find all posts View Profile Close D4Dazz]

Thanks for the info Leigh.

On a separate note I search multiple treads to try and find information on solenoids verses DCDC charger and could not find too much information. If this thread is boring you don't reply, and likewise don't recommend it be stopped by the moderators.

No use having a forum if you can't ask questions.....

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

You only need to do a search on dual battery systems there will be pages of hits.

No use having a forum if you need to search through pages and pages covering the
same info because every poster thinks his is the first time the question has been asked.

As to which is better, VSR or DCDC charger, that is up to the end user to determine.

Leigh

[ko7624 Junior Member Find all posts View Profile Close ko7624]

Hi Ken,

I'm just curious as to what information your basing your advice on, for
instance the Optima battery was specifically developed for use by the
American military and was specifically designed to charge rapidly off a
standard alternator setup?

One of the key selling points of the Optima is that they can be charged
from 0% SOC to over 90% SOC in under an hour. For example a D27 when
connected to a 100A alternator will recharge to 90% SOC in around 35 minutes,
If you put a 20A DCDC charger into the equation for a D27 the recharge time
would blow out to over 4 hours?

Also where did you obtain the data that supports a running a different
type of battery to the cranking battery as an aux via a conventional VSR
will shorten its life, I haven't seen anything written on any battery manufactures
website that would support such a claim?

Leigh

Leigh,

I presume you have the VSR system like many others and Im glad you're happy with it.

As I stated, a solenoid system WILL work but it may not be the BEST solution. Optima(from their US website) do state that their batteries can be charged by the alternator with no current limitation provided voltages are between 13.65 to 15.0v(Optima yellow top) and battery temps dont get too high. HOWEVER, they also state a few other things for optimal performance.... here's some quotes from their tech tip pages..... Im not sure if Im allowed to post links from non sponsors so I'll just paste quotes instead....

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged."

"An alternator is meant to maintain a battery, not charge it."

"Low and slow is best. A low amp charger (1 to 12-amps) is generally the best choice for charging any lead-acid battery. It's quicker to charge at higher amperage, but it also can generate a lot of heat, which reduces the life of a battery, just like the raging heat of summer."

And from thier FAQ page:

"If you are using an OPTIMA battery and a conventional battery, your system must charge each battery independently."

"No, when hooking batteries together in parallel, they should be of identical in age, size and type." (I presume this means permanent connections which are not like most 4wd dual battery systems)"

"Continued undercharging of a battery will lead to premature failure and a drop in capacity."

As for the solenoid shortening its life.....I stated it MIGHT shorten its life. I only states this because if the alternator output voltage reduces because it has less demand from the fully charged main battery, coupled with the temp compensated/emissions influenced charging system of the 150 prado voltages may not quite be at the optimal level... typically 14.7v for cyclic applications. This could lead to under charging and thus reduce battery.

To summarise my point of view, there are many who dont use dc-dc charges and their batteries are still charged and the system still works but the things I have read seem to point that it would be better for a different battery like AGMs to be charged with electronic/'smart' chargers as it should charge the batteries closer to its maximum capacity and maximise its life expectancy.

Now,

Would love to know if there are any auto electricians on the forum who may be able to clear this up. Don't want to be shelling out the extra cash for something I may not need.

D4Dazz, I am am auto electrician with 18 years experience. I can't tell you what you do or don't need but if your running a regular lead acid battery for a main and something different like an AGM battery for an aux and you can afford it, I would probably recommend the DC-DC charger set up for the reasons mentioned above. If you can't/don't want to afford the DC set up then the solenoid/VSR set up will still charge up your battery to some degree. Other posts have also revealed happy owners who have done the diode mod too.

Cheers,

Ken

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

Ken, As a auto electrician you should know that the vast majority of alternators have no way of knowing it if has either one, two or three batteries connected to it and certainly no idea as to the state of charge of each.

You should also know that the alternator in most vehicles does not reduce the charge rate to the cranking battery when it is fully charged as it has no way of knowing when the battery is fully charged, the battery takes what it wants, when a flat aux is connected it will also take what it wants. The only time it will reduce its charge voltage is in response to under bonnet temperature changes.

The Optima battery was designed for very rapid charging of an alternator, from Optimas website note the 100% dicharged or flat battery:

Recharge Time: (example assuming 100% discharge – 10.5 volts)

Recharge Time:
(example assuming 100% discharge – 10.5 volts)
Current Approximate time to 90% charge
100 amps
50 amps
25 amps
35 minutes
75 minutes
140 minutes


You have also taken extracts with regards to different usages ie:

Alternator
Battery Charger (Constant Voltage)
Float Charge
Rapid Recharge Constant voltage charger

and applied these to alternator charging, the charge source determines what charging method is applied, yes the battery will last longer if charged at a lower rate but who is going to charge a battery at 2A when it is required to run a typical dual battery setup?

As for:

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged."

Obviously if the cranking battery is flat your going to use a charger to get it going, jump starting and running the car and running for a couple of hours though would achieve the same result as charging with a 6A charger for 11 hours!

"An alternator is meant to maintain a battery, not charge it."

Contradicts their charging statement above, no doubt this statement is with regards to highly temperature compensated alternators, this can be overcome with the use of the booster diode. As I pointed out above, a DCDC charger and standard alternator charge at around the same voltage, so if you can't charge it with an alternator, you can't charge it will a DCDC charger either.

"If you are using an OPTIMA battery and a conventional battery, your system must charge each battery independently."

No doubt refers to charging with a charger.

The rest is common sense.

Leigh

[leachy_9 Advanced Member Find all posts View Profile Close leachy_9]

Additional to what Leigh has written, below is a link that dispels many of the myths around paralleling different battery types. The paper was written by Jim McDowall who is a current member and former Chair of the board of directors of the Electricity Storage Association. He is currently the Standards Coordinator of the IEEE Stationary Battery Committee and Chair of three of its working groups, as well as being a former Chair of the parent committee.

http://www.battcon.com/PapersFinal20...lPaper2002.pdf

[ko7624 Junior Member Find all posts View Profile Close ko7624]

Ken, As a auto electrician you should know that the vast majority of alternators have no way of knowing it if has either one, two or three batteries connected to it and certainly no idea as to the state of charge of each.

You should also know that the alternator in most vehicles does not reduce the charge rate to the cranking battery when it is fully charged as it has no way of knowing when the battery is fully charged, the battery takes what it wants, when a flat aux is connected it will also take what it wants. The only time it will reduce its charge voltage is in response to under bonnet temperature changes.

Yes that's right, the alternator doesn't know how many batteries it has connected. It only knows how much current is trying to be drawn from the circuit and thus attempts to change its current and voltage levels to compensate for the measured load. Under bonnet temp changes do effect its output but so too does current demand.

The Optima battery was designed for very rapid charging of an alternator, from Optimas website note the 100% dicharged or flat battery:

Recharge Time: (example assuming 100% discharge – 10.5 volts)

Recharge Time:
(example assuming 100% discharge – 10.5 volts)
Current Approximate time to 90% charge
100 amps
50 amps
25 amps
35 minutes
75 minutes
[FONT=sans-serif]140 minutes

Not disagreeing here.. As I quoted from optima there is no current limitation as long as voltages are within tolerances when alternator charging.

You have also taken extracts with regards to different usages ie:

Alternator
Battery Charger (Constant Voltage)
Float Charge
Rapid Recharge Constant voltage charger

and applied these to alternator charging, the charge source determines what charging method is applied, yes the battery will last longer if charged at a lower rate
but who is going to charge a battery at 2A when it is required to run a typical dual battery setup?

The voltages of 13.65 to 15.0 volts I mentioned refer to general alternator charging for the yellow top. I did not quote float charge levels or similar. They each have somewhat different levels. As for 2amp charge, Optima stated "1 to 12amps" is best for any battery. They can take higher amounts but higher charge means higher temps which means shorter battery life

As for:

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged."

Obviously if the cranking battery is flat your going to use a charger to get it going, jump starting and running the car and running for a couple of hours though would achieve the same result as charging with a 6A charger for 11 hours!

Can you show/explain how it would get to exactly the 'same' level of charge between the two? Again, I feel that an electronic or dc-dc charger can charge that final few stages (or last 10%) of the AGM battery if set correctly.

"An alternator is meant to maintain a battery, not charge it."

Contradicts their charging statement above, no doubt this statement is with regards to highly temperature compensated alternators, this can be overcome with the use of the booster diode. As I pointed out above, a DCDC charger and standard alternator charge at around the same voltage, so if you can't charge it with an alternator, you can't charge it will a DCDC charger either.

Their statement makes no mention of any particular type of alternator. DC chargers can have the same voltage at times as alternators which is fine for the bulk of charging but the DC charger can also have other phases of charging to optimize the battery charging and get the maximum charge back into it. Kind of like forcing the final 10% or so charge back into it.

"If you are using an OPTIMA battery and a conventional battery, your system must charge each battery independently."

No doubt refers to charging with a charger.

Actually its not referring to a charger it is actually referring to an isolator set up. Please have a read of it yourself.

Can I also ask what type of dual battery system do you have? Your signature/sign off at the bottom states you have a Rotronics system. Is that still right? They are quite a fancy system from what Ive been told and are more than just a voltage sensing relay or basic solenoid system aren't they? From the looks of it they can charge their batteries independently and are quoted as being "Designed for dissimilar battery types" accoring to their website.

I still stand by my recommendation to D4Dazz that the solenoid system will work but the DC charger will charge your aux(particularly AGM battery) a little bit better.

Cheers,

Ken

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

"Yes that's right, the alternator doesn't know how many batteries it has connected. It only knows how much current is trying to be drawn from the circuit and thus attempts to change its current and voltage levels to compensate for the measured load. Under bonnet temp changes do effect its output but so too does current demand."

Ken the "attempts to change its current" is not correct, as you know or should know a standard alternator is a float charger, the regulator only monitors and adjusts the voltage, it does not monitor the current output.

The Optima was specifically designed for rapid charging off an alternator for the American military yes it can be used for other applications but was specifically designed for automotive use, rapid recharging is its biggest selling point, the use of a DCDC charger unless it has a large output capability inhibits this.

"Can you show/explain how it would get to exactly the 'same' level of charge between the two? Again, I feel that an electronic or dc-dc charger can charge that final few stages (or last 10%) of the AGM battery if set correctly."

Simple basic chemistry, as long as the charging voltage applied to a battery is greater than the resting terminal voltage of the fully charged battery the battery will eventually fully charge. In the case of the Optima, its fully charged terminal voltage is around 13.1V as long as the alternators output voltage is greater than this the battery will eventually fully charge, yes it will take longer for the last 5% of SOC than a charger with a boost function (that works effectively) could do it but the alternator will do the bulk charge much quicker, ie the first 95% much quicker.


"Their statement makes no mention of any particular type of alternator. DC chargers can have the same voltage at times as alternators which is fine for the bulk of charging but the DC charger can also have other phases of charging to optimize the battery charging and get the maximum charge back into it. Kind of like forcing the final 10% or so charge back into it."

AS I have already pointed out, the two most popular DCDC chargers on the market, Redarc & Ctek have a maximum output voltage that is more the same as an altenator, they all use the same voltages because it was determined a 100 years or so ago when batteries when lead acid batteries statred being produced that 14.4V or there abouts is the best voltage to charge them at and it hasn't chaneg since. As the DCDC chargers use the same voltage as an standard alternator how can they charge a battery better? As I pointed out you don't need to force charge the battery.

Another point that never gets raised is the so called "boost charge" effectiveness of the so called smart chargers. The smart charger could be connected to any size battery, ie it could be a 35Ah or a 200Ah, it has no way of determining what size the battery is. The only chargers that can really do an effective boost charge are the ones where you can specify the battery capacity of the battery being charged, all others will approximate if they do one at all, ie smaller batteries will be overcharged, larger batteries will be under charged. On both Redarc's & CTEK's websites I find that neither actually does a boost cycle.

In the case of the larger batteries an alternator will actually do a better job as it will continue on at its float voltage ie 14.4V, the smart charger on the other hand will drop to its float voltage of around 13.5V and take considerably longer to get to the magic 100% SOC that everyone threats over.

From Optimas website:

Will my high-output alternator damage the OPTIMA^® battery?

No, as long as the voltage is properly regulated. Because the OPTIMA battery has a very low internal resistance, it will accept high current more efficiently than conventional batteries, ie it was specifically designed to accept high charge currents.


Do I need a special charger for my OPTIMA^® battery?

For regular charging we recommend a maximum of 10-amps, 13.8-15.0 volts. For float charging, we recommend 1 amp maximum, 13.2-13.8 volts.

Obviously the section you referred to is specific for when the battery will be charged by a battery charger on a permanent basis ie standy power / solar etc and not relevant for charging by alternator.



Yes I have a Rotronics system, the charge independent feature refers to the isolators ability to disconnect the cranking battery from the charging system. This is done to steer all available alternator reserve capacity to the aux for rapid charging, it has nothing to do with charging dissimilar battery types. The alternator will still charge at the same float voltage, you can also select to charge cranking battery only, or both cranking battery and aux in parallel.

I also find it strange that you are quoting manufactures glossy info and not speaking from practical installation and operational experience of an auto electrician of 18 years or are you one of those autoelects that recommends / installs systems but doesn't actually use them yourself for extensive touring etc to find out if they actually work effectively?

I would have also thought that with so much practical experience you would also have a better grasp of the basic functionality of the alternator voltage regulator

Leigh

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

ko7624,

An example for you to ponder, was recently discussing a problem friend had with his dual battery system. He recently did the Canning stock route and had trouble maintaining battery charge to keep the fridge running.

His setup is a Redarc 20A DCDC charger, Optima cranking and aux batteries in car and an other brand AGM in his TVAN.

His problem was with all the constant stopping and starting, ie drive for 30 minutes, stop for
an hour or more as members tackled dunes then drive for another 30 minutes etc he just couldn't get enough charge into the aux's to keep the fridge running overnight.

I pointed out to him the DCDC is acting as a bottle neck and slowing the charging process, if he had got rid of the charger he would have been able to bring the Optima in car upto 90% SOC in a around 50 minutes and the other AGM not that far behind and his problem would not have occurred.

He had a piranha setup before (non DCDC charger) and did not suffer from the same issue, last time I spoke to him he was pulling out the Redarc and replacing it with the old Piranha unit.

Leigh

[vk2ss55 Senior Member Find all posts View Profile Close vk2ss55]

Hey Leigh is this hall effect in an obvious location ...straight on the neg batt cable ?
Cheers Ross

[ko7624 Junior Member Find all posts View Profile Close ko7624]

Some DC chargers I know of don't care about constant stop and start short drives too much as they will charge the aux battery from the main even whilst the vehicle is not running. They obviously have protection to cut out so as not to flatten the main to the point of start up failure.

If charging 'speed' is an issue Id first recommend using a higher capacity DC charger ie 40+ amps or if that isnt preferred use the alternator for quick bulk charge then switch over to the dc charger for the final stages of charging.

I have quoted from places such as Optima because they are a giant battery company and feel that they should have a good grasp on the subject. If you want my personal experience, well I used to install traditional type isolator systems but found that the majority of brands would fail in a couple of aspects. One is that the deep cycle aux battery had a relatively short service life(my subjective observation) when using a load tester and the secondly and arguably more important was that they would develop an unnecessary current drain with the vehicle switched off and thus flatten one or both batteries. This was noticed on several brands of systems. Prior to DC chargers coming into the retail market we switched over to a basic 70 amp relay system for simplicity and reliability. It worked well for older style vehicles. Since then I have definitely moved towards DC chargers for many(but not all) installations. Optima batteries are the main ones I now deal with(but am not endorsing any one brand) and have several batteries up to 7 years old still testing within their CCA and AH specifications. Im not saying this is conclusive proof of anything as a lot has changed over the years in terms of electronics and battery construction but its my recommended way of doing things.

D4Dazz, I hope this thread has been of some help to you in deciding what system you decide on.