Is there the need to use a dummy load on an auxiliary battery?

[Doug32 Member Find all posts View Profile Close Doug32]

A friend told me that it does not do the auxiliary battery much good having it hooked up to the charge system (via an isolator) without also drawing current from it from time to time. Is this right? I only draw on the auxiliary battery when on camping trips for running the fridge and lights etc. Between trips there is no current draw but just sits in the charge circuit. Should I run the battery partly down on a regular basis between trips using a dummy load? The battery is a deep cycle marine unit.
Thanks in advance.

[Guest Close Guest]

I've been told to use the battery from time to time as well. But mine is portable and is removed from the Prado when not on trips.

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

Normal driving each day it won't be a problem, cycling the battery will eventually wear it out. I would however avoid leaving any battery on charge 24/7 though as I don't believe this is good for any battery.

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

this is one of the advantages of a DC/DC charger
As they are multistage if the battery is charged they will just supply a float charge at the correct voltage for the battery.
if you were to do a long trip with nothing being used from the AUX it would just sit at the float voltage and current.
In simple terms it works like a trickle charger once the battery is charged, you could drive as far as you like with no damage to the battery.

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

Actually that is not the case, depending on the battery, float charge voltages can
become critical when batteries are being charged for long periods of time be it at
14.4V or 13.5V etc. There has be a lot of discussion on another forum regarding
premature death of gel types batteries in campers when left on charge on smart
chargers 24/7.

In a in car situation charge times are generally not going to be an issue, most AGM's
wet cells etc manufactures specify that their batteries can continue to charge
at normal voltages for up to 24 hours, longer than that float voltages become critical
and unless your charger allows user setting of the float voltage your charger is unlikley
to meet the exact requirement of the battery.

Most users with a VSR setup don't use the aux around town and will have no issues, think also about your cranking battery, after 30 minutes or so drive it will also be near fully charged are you worried about it?

In pracitcal cyclic use it is unlikely the battery will ever be fully charged in a normal
days drive if charged of the alternator or DCDC charger.

One could also argue that the multistage function becomes a liabililty when the battery
is being charged with a load connected ie a fridge, the charger will return to boost charge
which could be upto to 15V@24C when the fridge starts thinking the battery isn't fully charged,
and will continue at that rate till the fridge turns off and the charger decides the battery is
actual charged.

All setups are a comprise in some way.

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

A friend told me that it does not do the auxiliary battery much good having it hooked up to the charge system (via an isolator) without also drawing current from it from time to time. Is this right? I only draw on the auxiliary battery when on camping trips for running the fridge and lights etc. Between trips there is no current draw but just sits in the charge circuit. Should I run the battery partly down on a regular basis between trips using a dummy load? The battery is a deep cycle marine unit.
Thanks in advance.

No it's not right.
The battery does not need to be cycled.
The best way to keep a battery is full.

[120D4D Avid PP Poster! Find all posts View Profile Close 120D4D]

One could also argue that the multistage function becomes a liabililty when the battery
is being charged with a load connected ie a fridge, the charger will return to boost charge
which could be upto to 15V@24C when the fridge starts thinking the battery isn't fully charged,
and will continue at that rate till the fridge turns off and the charger decides the battery is
actual charged.

All setups are a comprise in some way.

This is what worries me about my DCDC set-up - When the Waeco cycles the charger kicks-up to boost or absorption mode. Guess this is why the manufacturer suggest running it on the 'softest' setting AGM and not wet or calcium, regardess of battery its charging...

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

Some of the charger manufactures don't mention not to have anything connected to the battery whilst its being charged as they know in most cases this is impractical. Others state not to or you can but we don't recommend it. Simple fact is anything connected to the battery whilst it is being charged with a charger is going to give the charger a false indication of the real SOC of the battery.

As I wrote above, it depends on setup you have and how you use it as to what's best for you. Many are very happy with their VSR setups, others with DCDC charger setups, I have seen others "upgrade" from VSR setups to DCDC chargers only to find it doesn't work as well as their old VSR setup and revert back again. I have seen others with trailer that had DCDC chargers and were happy with them find that when they for instance added a CPAP machine to the mix found the DCDC not to be up to it and changed to a VSR setup and found it worked much better. Mind you fitting a 40A DCDC might also have solved the issue as it should give similar performance to an alternator but the price is the killer.

As an interesting aside, DCDC chargers are simply a persudo alternators for when you can't get a reasonable charge voltage from your alternator. A 40A DCDC charger should give similar or better performance charging a 100Ah trailer battery to the alternator, in car a little slower, the intersting point though is that there has been quite a bit of discussion on other forums of 40A DCDC chargers overcharging batteries and causing them to boil or swell, this does not happen with similar VSR setups yet the bulk charge voltages are very similar, Could again be accessories causing the issue, maybe not. The manufacturer of the charger suggestion was again to set it for a battery type to give the lowest charge rate, sometimes smart chargers can be to smart for their good as I recently found out with a NOCO cnarger but that is another story.

If what you've got works for you then great, if your thinking of installing a system then sit down and think about how your going to use it and do some research as to what's best for you but don't believe everything you read in the glossies.

You may even find if your only going to run a few led lights and a pump for instance a couple of weekends a year that a simple portable battery setup that can be charged when you get home will do the job.

[crog Lurker Find all posts View Profile Close crog]

Why when batteries self discharge, as long as you are providing a suitable float voltage the self discharge will stir the electrolyte and then when battery terminal voltage hits charging voltage then battery will draw no current.

Only issue you will have is if you float voltage is too high which would explain the swelling people are talking about. What is your charging voltage ??

By way of explaination we run10 year standby batteries in communications on constant charge and some of these never draw a load they are kept on charge .

Three things kill batteries 1. overcharging 2. too many deep discharges (sulfation which reduces capacity) 3. number of recharge cycles

If your float charge is ok and you are running a VRLA gel battery leve it alone and forget trying to cycle it

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

"Why when batteries self discharge, as long as you are providing a suitable float voltage the self discharge will stir the electrolyte and then when battery terminal voltage hits charging voltage then battery will draw no current."

The self discharge of a battery will not stir the electrolyte, it will result in stratification which is why most manufacturers recommend a regularr boost charge to stir the electrolyte. A battery will always draw current, it does not draw "no current" when it reaches the float voltage.

"Only issue you will have is if you float voltage is too high which would explain the swelling people are talking about. What is your charging voltage ??"

If you read what I wrote and have any idea of how multi stage chargers work you should know what voltages are being discussed?

"By way of explaination we run10 year standby batteries in communications on constant charge and some of these never draw a load they are kept on charge ."

I also have spent more years than I care to recall involved with telco no break power supplies, the float voltages used in a controlled enviroment charging batteries 24/7 that seldom get used are not applicable to those used in an automotive cyclic enviroment as the service requirements are completely different. All batteries draw some current at the float voltage unless the float voltage is less than the normal open termianal voltage of the fully charged battery in which case it is no longer a charging voltage!

"Three things kill batteries 1. overcharging 2. too many deep discharges (sulfation which reduces capacity) 3. number of recharge cycles"

Overcharging can kill a battery if excessive, a battery even being charged at 13.5V it will eventually be fully charged and it could be argued that after that time you are overcharging it.

Sulfation is not caused by deep discharge, a battery can only sulfate if it is not being charged or discharged, granted leaving a battery in a deeply discharged state will cause sulphation.

Number of cycles are not killing the battery, they are aging it, if it has a cyclic life of 3000 cycles at a depth of discharge of 50%SOC and we run it through 3000 cycles we have not killed it, we have worn it out!

"If your float charge is ok and you are running a VRLA gel battery leve it alone and forget trying to cycle it"

That is a real open statement, float voltages can become critical for VRLA batteries charged 24/7, all manufacures state that when charging VRLA batteries 24/7 that their recommend float voltages must be used, as few if any on this forum will have a charge source that will accept user settings that will be a little hard to achieve.

Also many camper trailers / caravans / boats use VRLA or gel batteries, these are charged either by are charger or direclty of the car towing them, and certainly wouldn't conform with the manufactures recommendations, as I have written elsewhere, dual battery systems are a comprise to meet a specific requirement.

I would not cycle the batteries myself, but then I would not charge them 24/7 either, in car with normal driving shouldn't be an issue leaving the battery connected.