What charging system to buy for aux battery?

Thanks Mick, a lot to consider there. My solar panels have a SBC2106 regulator all nicely sealed/waterproofed on them, I'd have to check if that is compatible with the nifty MPPT (Maximum Power Point Tracking) of the BCDC1240 if I was to go that path. Squeezing every last drop out of the natural light means being able to enjoy the serenity with a cold beer and without an engine running. I did get a 100W panel for a little overkill, but I've read all the posts on higher fridge power needs vs degraded panel operation in the heat, getting a bit more out of the panel would be a nice bonus with this system.

Mick,

Agree with most of your comments, BUT...... the BCDC 12/40 delivers 40 amps when bulk charging. This is fine with a big battery bank such as yours, but IMHO is really too high for any 100 Ah battery. Pity its little brother, the 12/20 doesn't include the solar controller, as that would otherwise be the ideal choice for this application and a local product too. The Ctek D250S Dual charger provides the solar MPPT controller plus a 20 amp dc-dc charger and might be a suitable choice for a 100Ah battery. (I understand its downside is that it spends too long in absorption mode.)

Something to watch with dc-dc chargers delivering high current is the drain on the alternator. eg there may well be 45 or more amps drawn from the alternator to deliver 40 amps to the battery. If it's a 50 amp alternator there isn't much left for other purposes, and when the alternator sags under the load, more current will be drawn to keep up that 40 amps delivery. You can (and I have!) got into a pretty fast downward spiral leading to a new alternator. (and I was using a 30A dc-dc charger with 200 Ah of battery.)

Another thing worth consideraing - The intermittent loading of the battery by the fridge can trick some dc-dc chargers into starting their bulk/absorption/float routine when in fact the battery is fully charged. Generally a timer controls the duration of the constant voltage (absorption) phase, so some chargers will attempt to push high current into the battery for hours after it is fully charged... not good. I'd suggest to anyone running a big dc-dc charger that they fit a relay to draw fridge current from the alternator (ie the input side of the dc-dc charger) when charging current is available, and from the battery (ie the output side) at other times - I use a headlight changeover relay for this - works well and avoids intermittent loading on the charger's output.

Cheers

John

Walkaway,

Note your above response to Mick - arrived while I wasn't looking! Pity you have a controller on the panels, as it is far better if they are close to the battery. If you use the one on the panels it will not be possible to make use of another MPPT one wired after it.

Cheers

John

Walkaway/John,

Regarding the solar controller - can the panel mounted unit not be circumvented to provide open current from the panel to the Redarc controller. As in my 100W bi-fold, the controller has a wiring block underneath. I have had the panels wired around the existing controller. It can easily be reconnected should I be using it for another purpose outside the inbuilt MPPT in the Redarc.

John, I'm actually using the Redarc BMS 12/15 system over the larger battery bank and the BCDC within the vehicle system for the auxiliary battery. The auxiliary in the vehicle is an emergency and back-up system only through a switched solenoid for times of high energy need (winching for example) or if I get a flat main vehicle battery.

I'll defer to expertise here (because I'm certainly not one) but it was my understanding that the BCDC unit will only deliver 40 Amps to a battery in conditions where it is needed and that in normal operating circumstances, the unit will sense what is the most appropriate input for the absorption stage determined by the type of battery being charged and the current State of Charge of that battery. Am I missing something here?

The alternator issue is not one I'd considered previously and certainly something that needs to be considered in the context of a system overall particularly if you are drawing a lot of power from your batteries each day.

I've been using the my 100W bi-fold solar going into the BMS on the occasions that I'm sitting still long enough but am currently assessing my solar needs for fixing to the vehicle in November (funding approved by the Minister for War and Finance). I'm looking at 3 or 4 x 95W panels roof mounted in a frame that is adjustable for sun angle. While the BMS has only a 15A max input for the solar, peak sun production would only max that on a rare occasion using the 4 panel situation only. While it won't "over charge" the batteries, the averaged high production from the 4 panels will allow me to maintain high rates of charging for longer each day or in poor light conditions.Well thats my thinking anyway.

Walkaway, as Mick says, you may be able to connect to your panels ahead of the panel mounted regulator and run from there to an MPPT controller close to the battery. Fine if you can, but from what you said initially it sounds as if it is nicely potted in epoxy and not accessible.

Mick - The BCDC 12/40 will be a bit vigorous for anything but a pretty upmarket heavy duty battery, spiral wound or similar. Suggest check that the manufacturers recommend charging at up to 40 amps.

These (and other multistage) chargers basic operation consists of pumping in charge, subject to not exceeding some maximum voltage and current. Initially, during the "bulk" charge phase they provide a voltage sufficient to push charge into the battery at the rated rate (eg 40 amps). As charge accumulates in the battery the charger voltage increases to maintain this rate of charge, until the voltage reaches a predefined level (typically 14.2 to 14.8 volts dependent on the type of battery). This voltage is then held steady, usually for a defined period of time (2hrs.. up to about 10 hours in some chargers) during which the charging current declines to a low level. Some chargers follow the better approach of maintaining this steady maximum voltage until the current drops to some predetermined low level (typically 1 or 2amps). Followinng the constant voltage (absorption) phase the charger will drop the voltage down to a float phase (typically 13.2 - 13.5) which maintains a trickle charge into the battery. While there are multistage chargers that have more phases and perform extra functions, their fundamental operation is as above, and the extra phases have more to do with marketing than with charging!

So, you ask "am I missing something?" in thinking that the charger will adapt to the battery's characteristics and its charging needs. In so far as it performs as above, and the above satisfies the requirements, No. If though you credit the charger with enough electronic intelligence to sort it all out, Yes.

The simple facts are that charge will be sent into your battery at the rate of 40 amps until the terminal voltage rises to about 14.5 volts. This voltage will then be maintained for a period before the charger drops it to some float level. The charger isn't doing any thinking, simply what it was programmed to do - maintain constant current and constant voltage conditions. It relies in essence on the user setting the two critical voltages according to the type of battery (gel, agm, west, calcium etc), and the assumption that the battery can accept the rated charging current.

It is this final assumption I'd be concerned about. I wouldn't send 40A into anything less than a 200 Ah battery bank or a big spiral wound cranking battery.

Hope that clarifies and doesn't start too many arguments with the marketting people!


Mick - don't want to hijack Walkabout's thread, but an aside - I think if you go for 4 panels your 380W of solar capacity is a far more than you'll be able to make use of. We carried 200W on our recent trip, but thanks to the 30A dc-dc charger and 200Ah storage, hardly used it at all. When we did stop for some time the 200W exceeded our daily requirements. 380W of panels will deliver about 22 amps (even more under scattered cloud) and I doubt that your 15 amp controller will handle that.


Cheers

John

Thanks John. Appreciate the advice. Re the solar, I was leaning towards the 3 panel set up (285W total). I have 280 A/H of onboard AGM but the big fridge freezer can chew through a bit in the hotter climates. I'm looking at some other appliances that can draw a bit during use as well. Being fixed panels, I didn't expect to have the flexibility of the moveable folding panels so anticipated sacrificing some effeciency in collection rate there.

Cheers Mick

John,

My regulators (one on the back of each panel) are well and truly potted though that wouldn't stop me cutting the 5 cm of cable from panel to reg if needs be and splicing in whatever I wanted. I did find my regs in a jaycar catalog for $50 each and MPPT regs for $250 each so now I know the difference.

Thanks for the multistage description, I thought there was more intelligence in there. It seems what I need is to just rig up my panels across the aux battery seeing as they have regs in them already and find a 20A dual battery system for an AGM, like the Projecta DC20 Patrol22 suggested. I'm slightly concerned by the $200 difference in RRP of the Projecta at $300 and the Redarc BCDC1220 at $500. It does seem from reading the specs that the Redarc is set up for some very hostile environments, whereas for me it will be running inside my passenger cabin. Perhaps it is branding and this healthy design overkill that accounts for the difference?

Looking now I see that for an AGM it is Redarc: Bulk 12v, Absorption 14.5v and Float 13.3 and Projecta (max current, up to 14.1V)/14.4V/13.7V.

Feel free to correct anything I've got wrong or else I may just end up ordering a Projecta DC20, ie. save me from myself :)

The BCDC1240 will deliver up to 40 amps of charge with emphasis on "up to 40 amps".... same as an alternator will deliver up to 100+ amps.

The BCDC will tapper off it's charge current as the BCDC's case temp increases (dependent on where it is mounted).

Most people with aux battery systems use a simple VSR (voltage sensitive relay) and do not use a DC-DC charger that limit current inflow into the aux battery meaning there battery is getting what ever current the alternator want to put out.... using a VSR a low SOC aux battery may see as much as 300 to 400 amps in rush current at the initial cut in phase until it settles down and accepts a charge rate determined by the alternator.... this charge rate from the alternator maybe somewhere between 13v to 16v depending on vehicle and type of battery fitted as OEM.... the charge current may be anything from 10amps up to 60amps+.

I would say you would have less chance of destroying a battery with a BCDC1240 then trying to charge a batter at a lower or higher voltage of the alternator with no current limiting or true charge algorithm.

All batteries have a sweet point for charging whether it's voltage, current or temp... in most cases it's all three..... a battery being charged under the ideal environment will last a long time.... an automotive environment is not the idea environment.

As you know Mick;RedArc went into a fair bit of detail ensuring it would be OK to use with you aux battery under the bonnet before supplying it to you.


Here is the specs for charging an Optima Yellow top battery....

Alternator: 13.65 to 15.0 volts
Battery Charger (Constant Voltage): 13.8 to 15.0 volts; 10 amps maximum; 6-12 hours approximate
Float Charge: 13.2 to 13.8 volts; 1 amp maximum (indefinite time at lower
voltages)
Rapid Recharge:
(Constant voltage charger)
Maximum voltage 15.6 volts. No current limit as long as battery
temperature remains below 125°F (51.7°C). Charge until
current drops below 1 amp.
Cyclic or Series String Applications: 14.7 volts. No current limit as long as battery temperature
remains below 125°F (51.7°C). When current falls below 1 amp, finish with 3 amp constant current for 1 hour.

All limits must be strictly adhered to.
Recharge Time: (example assuming 100% discharge – 10.5 volts)
Current Approx. time to 90% charge
100 amps 52 minutes
50 amps 112 minutes
25 amps 210 minutes

Walkaway,

Did a quick scan through ebay. (It’s a very useful catalogue regardless of buying preferences.) I saw 3 obvious options for your 20A dc-dc charger. Redarc BCDC1220 at $350-$450, Ctek D250S dual at a bit under $300, and the Projecta DC20 at about $225.

I’m not personally familiar with any of them, but judging by the specs and thinking of value for money, I’d go for the Projecta DC20 unless you’d like to allow for an MPPT controller, in which case I’d opt for the Ctek D250S Dual. (Note that the “Dual” is important as it indicates that the charger includes the solar controller.) I can see no justification for the high price of the Redarc, though as others have said Redarc have a good reputation for quality gear, and Australian, so well supported locally.

Olcoolone – I disagree with much of what you say. Particularly, I’d warn against using the Optima battery as a model. This is a very expensive spiral wound type with exceptional specs and not typical of what most of us use. Charge in less than an hour at 100 amps? “Tell ‘im he’s dreaming!”

Cheers

John

olcoolone wont waste my time commenting on your post. See if TAFE have a low voltage course you can take.
Optima batteries

John the Ctek D250S Dual is the best buy. Projecta needs ignition feed to isolate and does not have a built in isolator like Ctek and Redarc. Projecta and Redarc have crude charging profile not ideal to modern sealed batteries. Having a charger of any type without pulse charging today is bad news. The Redarc BCDC1220 is seriously over priced for a poorly engineered design. While the Ctek has an excellent charging profile, and a built in MPPT solar controller, you do need minimum 120W of solar panel capacity to get the MPPT solar charger to operate correctly.

John how can you make comment when you have no personal experience with any Dc-Dc charger.

The Optima was put in the post as an example of charge rates that batteries have.... The Optima was an example.

By the way I don't use or recommend Optima batteries.




And P2D2 funny it's my trade and aren't you the one who tries to sells and recommends the Ctek DC-DC charger and knock every other brand!

Please tell me the TAFE course I should be undertaking.... whats the name of it and what is the course number?

How many hours is the module and whats covered.... please enlighten me.

Have you done the TAFE course your refering to?

Did you mention the Ctek is the best in you post .... oh yeah I see you did.

What was the name you went under before on this forum until you got forced into changing you user name ?

It seems you know a lot about the Ctek and very little about the other DC-DC chagers on the market.... Oh thats right I forgot you only sell and recommend the Ctek.

Oh and please supply the data and tests completed to back your claim about the other two DC-DC chargers mentioned.

Enough said!

Thanks gents, the topic seems to have produced some sound advice. It would be a shame to see this detracted from. Lets try and assist the postee rather than have the matter degenerate.

Kind thanks,

Modsquad

Thanks Patrol22, alternative options are always welcome, nice little video explanation on that unit; I did see plenty of Projecta at the weekend leisureshow but I'd hit my limit of making informed decisions by that point :)

If you check the specs of all the DC/DC chargers, Ctek is an easy winner.

Redarc just another tired outdated old fashioned behind the times dinosaur Australian company.

Have you pair of baggers got any particular qualifications to back up your statements, or are you just flaming?

Bill is not a bagging or flaming, a truthful statement of fact. Reason we import so much from countries that believe in education, science and quality engineering. Australia believes in beer and football LOL

Ahh Paul, you’re back. From your own admissions in previous posts, don’t you field test a specific manufacturers products in return for freebies? Yeah that’s you. Good to see a couple of obvious whankers bagging an Australian company of some repute from behind the gutless anonymity of a dodgy screen name using nothing more than their own self interest as motive. Always brave to make unqualified statements as ridiculous as both of yours. Seems Olcoolone was correct about you P2Don't2 the way you have gushed over every post regarding CTek. Put up or shut up.

IMHO, Ill informed, self interested and un-Australian the both of you.

Bob the D250S has been discontinued. The functionality of the D250S Dual makes it suit a wider market and enables other extra options other than adding a solar panel.