Battery Charger for camper trailer battery

Trevor
If you have an 80A alternator that has 50A spare after powering the car why choke the charge back to 25A as all that does is slow the charge rate down until the battery gets to around 75% before you really get the benefit of that system which is only beneficial after that point.
A true smart charger will convert all the alternators surplus capacity into battery capacity and with temperature compensation you can get more than double the AH recovery in the same time frame.
Run time costs money and the slower the charge recovery the load sustained on the alternator costs extra fuel.
An 80 A alternator has a contiuous duty of 48A so convert as much of that 48A into stored battery capacity as possible in the shortest time.
Ian

Ian,

You keep coming up with this and I understand that the Ranox doesn't have the rated output of the units you sell. But fitting a booster such as the Ranox doesn't 'choke back' the alternator input to the battery.

Do you think that with no voltage regulation (ie, a straight alternator feed) that the battery is getting anything like the 48A 'spare' capacity?

I understand that the point you are trying to make (subtly) is that your Stirling units have a higher output. That's fine, but it is misleading to suggest that the Ranox unit 'chokes back' anything.

Why 25A maximum for the Ranox? My guess is that the manufacturers have no control over the quality/size of wiring used or the maximum acceptable charge for the batteries being charged. So 25A is a 'safe' compromise. Someone who doesn't know what they are doing trying to push 50A into a small aux battery over thin wiring, could be asking for trouble.

I know the Stirling units have a higher output (and they cost a fair bit more by the way), but the Ranox, for most applications actually boosts the charge, not chokes it.

Matt.

Matt
That most applications of boost would be with a battery above 75% SOC but if you have no other charge and rely on DC to DC only I think your statement is misleading if the battery needing the charge is below 75%SOC.
All things equal and correct cable sizing and BTW you pay for capacity and 100% increase in capacity does not cost 100% increase in cost with BtoB charging and that is the subtle efficiency difference
ian

Ian,

Even below 75% SOC the Ranox unit (at 25A output) will still charge quicker than a straight alternator output. Your assumption is that given correct size cabling, the battery will accept the alternator's spare output. But it is not just cabling (important though it is) that determines how much the battery accepts, but the voltage differential. Decent sized cabling serves to ensure that the voltage at the battery is a close as possible to that output by the alternator.

If the differential between the alternator output and the battery is small, then it doesn't matter how much amperage you have, the battery will not accept the charge at a decent rate. Increase the voltage differential, which is what units such as the Stirling and Ranox do, then you will force the battery accept increased charge.

As an example, my previous set up relied on straight alternator input to charge a 100Ah AGM aux battery, through an isolator (Redarc). I had fitted (don't ask me why) a 20A breaker at the cranking battery end. Over several years of use in a wide range of conditions and at varying states of charge for the aux battery, I never popped the breaker once.

Along comes the Ranox. Same battery, same cabling (6 B&S), same alternator, same everything but with the Ranox set at 25A max output. OK for a while, but the first time I went camping and used the battery for the weekend, I noticed that the battery wasn't charging, no power to the Ranox unit. Cursing, I did some more investigation and realised that the 20A breaker was tripping. Reset it and same again. Replaced the breaker with a 40A one, and no more problems.

So what this tells me is that, despite having ample alternator output, my aux battery never drew more than 20 Amps, regardless of its SoC from a straight alternator to battery set up. I honestly don't know what rate the battery charged at under the old set up as I never measured it. But it was certainly less than with the Ranox fitted. Just because the alternator outputs heaps of gibbers, doesn't mean the battery is accepting them.

Now, you can make an argument that Ranox should have designed their unit to output more than 25A and you can make an argument that the Stirling offers better, features, reliability, value for money, etc. That is fair enough. But to suggest that the Ranox somehow 'chokes' alternator output is, as I said, misleading. My experience would suggest the opposite.

Cheers,

Matt.

Thank you Matt for your response but you say you dont know what your old system produced so you are theorising on what benefit the Ranox gives you against the old system.

Your last paragraph confirms my statements in as much that you are limited to 25A and if the alternator has a higher continuous duty rating than 25A with spare capacity to use which most 4wds have and you do not take advantage of it then you are choking the alternator and the only limiting factor to that is the battery type and size you are using.
Ian

Ian,

You are misreading what I am saying.

I don't know what my old system put into the battery, but I DO know it was less than 20A (nothing like the alternator capacity). I DO know that the Ranox is providing MORE power than a non-boosted system. Maybe not as much as the Stirling units, but MORE than a non-boosted system. So it does not 'choke' the alternator capacity, quite the opposite.

Cheers,

Matt.

Matt
Read again what I said and forget about your old system its the balance of the post that counts.
Ian

I get what you are saying Ian, now you need to read what I am saying. I just have issue with the term 'choke'. The way you put it suggests that a unit such as the Ranox will slow charging down until the battery reaches 75% and be of no benefit over a non-boosted system. It won't, it will speed it up. Maybe not as much as your product, but speed it up nonetheless.

Matt

Sorry Matt Choke it is and choke will stay in my book as I know that more than 25A can be extracted from the average 4wd alternator battery type compatable.
BTW its beer oclock have a good one.
Ian

Well sorry Ian, misprepresenting other's products in order to sell your own it is and misprepresenting other's products in order to sell your own it willl stay in my book.

Enjoy your beer.

Matt
The misleading part comes from the product you are supporting and the site itself makes unsubstantiated claims of superioity.

I make no such claims and have tried to be within reason objective with what I believe can be proven.

I dont have to sell any product to exist so if i sell nothing it costs nothing so I have no reason to tell other then what I believe to be true.

That is my opinion and I will stand by it but if Im proven wrong I would be the first to admit that and stand corrected.
You are entitled to your opinion the same as we all are in life and what we accept we wear.
Im not going to choke on what I have said.
Cheers
Ian

Ian,

The only 'claims of superiority' the Ranox site makes is over a non-boosted direct charging system. To be fair, you are the one making direct claims of superiority in your initial reply.

I have also tried to be objective and have given you an example from my own experience which suggests that the Ranox claims are accurate, it does give better performance than a non-boosted system, using the same principles incidentally that the Stirling unit relies on. Just different specs, some different features and different price.

I don't want to give you the impression that I am wedded to the Ranox product, I am not. But I am a believer in the fact that these type of units do enhance charging performance. Is the Stirling unit a better one? I believe that it probably is from my reading on it, but it comes down to a value decision as always and doesn't automatically mean that the Ranox is a bad choice, which is what your initial reply suggests.

Cheers,

Matt.

Matt
I have visited the site in question and now agree that the site does not purport superiority and has been changed from the original site that made overt claims.
I had a serious phone conversation and made suggestions to a director of that firm and the wording "I believe" and "value for money" confirms that he listened although I doubt he will admit to the conversation which was instigated by him with an air of superiority.

I therefore unreservedly being true to my word retract that portion of my posting regarding superiority but I believe it still chokes the alternator.

Have a good night.
Ian

Fair enough. We'll agree to disagree on the last point.

Hope the beer was good.

Matt.

What I can’t understand is if your alternator is only producing 13.8 volts, as stated in their advertising hype, why you wouldn’t you go and see an auto electrician.

Even with the specialised charge voltages of some of the hi tech regulators now being put into vehicles, including 4x4s, the average 4x4 should have an output voltage of 14 to 14.2 volts.

The claims made on their site are based on a worst case scenario and in that case, anything would do a better job.

In the real world, where the vast majority of vehicles have properly functioning electrics, one of these wonder devices, and there have been a few of them, with a maximum, at best, of only 25 amps, is only good for an improvement over an alternator’s output, for charging a battery of up to about 70 A/H and an alternator would equal one of these thing up to a battery size of 100 A/H and anything over that and the alternator will easily replace more charge than this will.

Contrary to the claims made on their site, if you had adequately sized cable, which I might add, will cost a fraction of what this device costs, your average alternator will most definitely replace far more A/H where there are two 100 A/H batteries in need of a good charge.

The graph on their site is based on a best case scenario for their device, it’s just a shame that in the real world where the rest of us are, this situation is not likely to be the case.

The graph is next to useless as it doesn’t give either cable size or run length, it’s based on a vehicle with an output voltage that is below average. All deliberately misleading.

Most people regularly take their auxiliary batteries below 50% SoC not just 75% SoC and at these levels, a 25 amp booster would take around twice as long to replace the bulk of the charge in these two batteries as what an ordinary alternator will take.

Furthermore, in the real world, very, VERY few people drive long enough to fully charge their batteries but need to get as much bulk charge as they can in the short time they are driving and again, an alternator will replace heaps more A/H capacity then this or any 25 amp booster will do, with the only requirement being thick enough cable and the alternator will not only replace more capacity, it will do it about 40% more efficiently that these devices can.

In simple terms, if you have a total auxiliary battery capacity of only 70 A/H then a 25 amp booster will charge your battery, depending on the type of battery, quicker than an alternator will. If your total auxiliary battery capacity is between 70 and 100 A/H then it is about break even between this and your alternator and anything larger than 100 A/H, these things will take longer than an alternator will.

Drivesafe,

Not my 'real world' experience, read reply 4 above and my alternator outputs 14.1-14.4V no problems.

If 14.0-14.2V is fine, why do most (all?) 240V chargers have a bulk charge output of 14.4-14.8V? Would seem to be a waste of time and money if lower voltages are OK.

You say, "Even with the specialised charge voltages of some of the hi tech regulators now being put into vehicles, including 4x4s, the average 4x4 should have an output voltage of 14 to 14.2 volts". Talk to some Prado owners, they might disagree with you.

"Most people regularly take their auxiliary batteries below 50% SoC not just 75% SoC and at these levels, a 25 amp booster would take around twice as long to replace the bulk of the charge in these two batteries as what an ordinary alternator will take."

Again, this assumes that all of the alternator 'spare' capacity is making its way into the batteries, my understanding is that this is (primarily) a function of voltage differential, which is why 240V chargers and solar regulators bulk charge at a higher rate than the 14.2V output of your alternator. I would be interested if you could point me to some reliable information which helps me to understand why you would say this.

Cheers,

Matt.

Hi Matt, sorry mate but you have missed the point, the object of most RV users is to have enough stored capacity at the end of a days drive to be able to run the electrical accessories over night, if they are not stopping at a powered site.

In this case, even a small alternator will have sufficient capacity to easily charge 2 or 3 batteries at the same time and replace FAR more A/H capacity than what a 25 amp charger can do.

All the info being presented in this thread and on their web site relates to topping of the batteries. If all you ever going to need to do is top the batteries off then you obviously have more battery capacity than you need.

Again, in the real world, most people will have just enough capacity or at least try to set up to enough stored capacity to allow them to use the accessories as they wish. This means they will regularly take their batteries down to and below 50% SoC so they need to replace the bulk of their charge while they are driving, NOT just top the batteries off.

Even when using flooded wet cell batteries, the slowest batteries to recharge, a 100 A/H battery with an SoC of around 50% will easily pull 20+ amps when supplied with a charge voltage of 14v and if the battery has a lower SoC, the current draw is going to be even higher and if you use AGMs the current draw can be much higher again and even allowing for a voltage drop across the cable because of the current loads being required by the batteries will still see the batteries getting a higher charge capacity straight from the alternator.

If this device was great, why don’t they show a graph that more realistically represents what people actually do in the real world.

Going on that graph, in reality, what the manufacture is saying is that to make their product work better than what an alternator can do, you actually need to have carry 40 to 60% more battery capacity than you are ever going to use so that at any time you are only topping off partially discharged batteries, not recharging low batteries.

That makes sense, NOT. the math just does not add up in favour of the little 25 amp devices.

As I have posted, for a fraction of the cost of one of these thing and remember, you have a hidden additional cost of still having to buy fair large cable to allow this kind of device to run at or near 25 amps, so a heavy cable only set up will do a better job for about half the price.

Drivesafe,

And you missed my question. Simply because the alternator can output (pick a figure) say 50Amps of spare capacity, does that mean that a voltage of 14.2V is going to be sufficient to force the battery to accept the charge at that rate? You make this assumption, but I would still be interested if you could point me to a reliable source which confirms it.

I have, in the past, regularly run my batteries down to near the 50% SoC you talk about, yet my batteries have never drawn more than 20Amps from a decent sized alternator with a 14.1-14.2V output.

Once again, why do most chargers have a voltage significantly higher than 14.2V for the bulk charging stage? If the maths doesn't add up, I would like to understand the maths.

Cheers,

Matt.

Hi Matt, I’m not there to see what sort of set up you have so could you supply more details, EG, battery size and type, cable size and run length and what was the voltage at your auxiliary battery terminal.

From what you are saying, it sounds like you have a flooded wet cell or gel cell battery, correct this if not, and they will take that sort of current if they are getting 14,2 at the terminals, but, as I posted, there will be a voltage drop so the the draw current will be lower.

We are not talking about 1 battery, the graph specifically refers to 2 batteries, so the two batteries combined current of 25 amps means you are only supplying 12.5 amps AT BEST and these batteries will draw more than that straight off the alternator.

If we were talking about something like an Optima battery, these can take full inrush charge currents and I know for a fact that Discovery 3s can supply up 90+ amps when charging one of these types of batteries and that well over 3x what your device could ever hope to do.

Another point over looked is that there is usually a fridge and it’s current draw needs to be added to the equation and doing so would make the cable only set up even more advantageous.

As I have posted, I am not saying these devices can help i a very small number of cases, I am saying that in the vast majority of cases, they will NOT work as well as a correctly set up cable only system and this can be done for a lot cheaper set up cost.

And one more point I passed over before, you referred to “spare’ alternator capacity. You device requires a 40 amp input to achieve a 25 amp output and so if you were a bit short on the output capacity of an alternator, as you were trying to make out, as such, your device would actually suffer from a limited output capacity before a cable only set up would be. EG, going on your theory, if your alternator was limited to say only 30 amps being available, then your device would only be able to provide about 15 or 16 amps for charging while a cable only set up would still be ale to supply close to the full 30 amps.

As posted, none of the math adds up.

Thanks Derek, have been looking at your ABR 15 and 20Amp battery chargers. They seem to have the functions that we are after at a reasonable price. Any benefits to having 7 stages of charge over 3 stages of charge? Thanks for your advice.

Time is the main advantage 3 stage has over 5 or more stage chargers.

Some multi stage ones have a desulfate / recovery function.

If you can wait why not wait for our new pro-series chargers with PWM. The 3 stage with PWM is quicker and also recovers sulfated batteries.



Regards

Derek from ABR

Thanks for the headsup, will the wait be weeks or months??
What sort of charging rates will the range of these chargers have?

End of April. 20A and 40A with remote.

Derek

What do you think is a fair price to pay for a Fullriver 100-110A AGM battery. My second battery carked it’s self yesterday.

Regards

Kim

Hi Kim

$350 - $400 would be fair.

Regards

Derek

"Minimum of 10% of the battery capacity
Maximum is 25% of the battery capacity"

- I agree.

Mike and derek
Do you include high recombination AGM and Gel batteries in that minimum and maximum agreement.
Ian