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View Full Version : Advice on a charge controller please :)



blackburn mark
08-11-2012, 01:56 PM
not quite cnc related unless i end up living in my van (might happen the way the nhs is going)

i'm looking to run 12v dc from my van through this mppt charge controller

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is it possible to to connect the 12v dc into two of the AC inputs ?
or should i bypass the rectifier and add the 12v dc at the + and - in picture 2 ?

m_c
08-11-2012, 03:06 PM
What exactly are you trying to acheive?

You could connect the DC into the AC outputs, but you're going to get a voltdrop due to the rectifier diodes, so you could bypass them, if that's what the + and - are. You could also connect it through the solar panel connections.
However will that controller be able to handle the power from a high current source?

blackburn mark
08-11-2012, 03:56 PM
What exactly are you trying to acheive?

You could connect the DC into the AC outputs, but you're going to get a voltdrop due to the rectifier diodes, so you could bypass them, if that's what the + and - are. You could also connect it through the solar panel connections.
However will that controller be able to handle the power from a high current source?

I want to add a large solar panel so I don't want to use those inputs if I can help it
I assumed the controller would draw its maximum 600watts wind from the van and 200watts solar, I just need to knock off all the functions that are meant to protect your wind gen from over speed or it will start dumping energy through the dump load or isolate itself from the load altogether

I have taken I bit of a punt attempting to using this method but it should mean the two charge voltages wont compete with each other (one knocking the outer into thinking the batteries are full) as they would if I used two separate charge controllers... the more I squeeze out of the solar the less diesel ill use while driving is the theory

Jonathan
08-11-2012, 04:58 PM
What a co-incidence, last week I persuaded my Mum that solar panels were now cheap enough to pay for themselves in a realistic amount of time, so we bought 4*190W panels which will go on the shed. I've already got two suitable inverters, the batteries and cable (can get that from uni too), so it's going to be fairly cheap to do. I've now started designing an MPPT controller as they don't look that difficult, just a buck converter...famous last words perhaps!

Anyway, like m_c I'm not sure what you're trying to achieve here? Taking 12V dc from the van (battery, alternator?) through the controller into what... some batteries? If so why? Oh are you charging the van battery with solar to offset the power drawn from the engine via the alternator?

blackburn mark
08-11-2012, 06:01 PM
Anyway, like m_c I'm not sure what you're trying to achieve here? Taking 12V dc from the van (battery, alternator?) through the controller into what... some batteries? If so why? Oh are you charging the van battery with solar to offset the power drawn from the engine via the alternator?

I'm converting an extra long wheelbase sprinter van into a camper... I'm now at the point where I'm ready to add two 125ah batteries and wire it all up before i add to much of the interior that it becomes difficult to run wires up and down the length
i'm looking to fit a 250w panel on the roof so i'm not drawing current from the alternator all the time (wasting diesel) and i don't want to be reliant on running it just to charge the batteries, iv also the option of adding a wind gen if the need arises.

sooo... if the shit hits the fan at work and we all get laid off ill park up on the west coast of Scotland put a wind genny up and run my cnc once a week for my beans on toast :)

m_c
08-11-2012, 07:22 PM
Add an intelligent split charge system.
Otherwise if you want to bring the auxilliary batteries up quickly from the alternator, you won't be able to, and 600w is a pretty slow charge for that amount of capacity if they run flat, and that's if the charger can actually push out that amount.

I'm at work just now using my phone to reply, but I'll post later from a proper computer with some pointers for what you're trying to achieve.

WandrinAndy
08-11-2012, 07:36 PM
Mark, it might be worthwhile also searching / posting your query on the caravan forum at Caravan Talk Forum (http://www.caravantalk.co.uk/community/index.php)?

I've previously seen similar threads on there...

blackburn mark
08-11-2012, 08:06 PM
cheers Andy... iv done quite a bit on those forums etc... its the reason i committed to this charger, I couldn't afford the "morning star" or "sterling" stuff (well I could... but I refuse to)
I just came on here to confirm I would get away with jumping the built in rectifier on this model

the problem with the intelligent split charger (as I see it) is the lack of voltage, you only get what the alternator gives you, 13.4v I think it is in my van... I need the option to push up the volts to 14.8v and hold it there for however long it takes.

Jonathan
08-11-2012, 08:16 PM
If you're doing this purely for financial reasons, then it's a rather long winded way to earn money given that it will take at least 5 years for the electricity saved to pay for the panel if you get it at a good price. Have you worked out how overall how much energy each appliance requires and thus how long you can run the CNC router for using the remaining energy? Electricity from diesel should be cheaper than from using solar panels.

For beans on toast you want a solar oven :playful:

It's annoying that you have to use 12v not 24v, since apart from the efficiency you're limiting yourself to more expensive solar panels.

blackburn mark
08-11-2012, 08:37 PM
its not for financial reasons... its my little pipe dream to help me keep my chin up if i end up on the scrap heap
i like the idea of the old travelling knife sharpener :)
this charge controller will take 38v open circuit, i'm sure that's pretty typical for a cheap 250w panel

my cnc draws 130W 150W typically... it would draw a shitload much more if i leathered it but i took measurements on a typical run... my desktop will draw more than that when its rendering HD files
im pretty sure i could run for six hours before i got to 50% then sit in the dark until the sun comes up lol

Jonathan
08-11-2012, 09:55 PM
Hmm fair enough...


this charge controller will take 38v open circuit, i'm sure that's pretty typical for a cheap 250w panel

But does it accept 38V with a 12V battery on the output, or just with a 24V battery? Looks like you've got this one, but the listing isn't helpful:

800W Wind Solar Hybrid Mppt Controller (600W Wind + 300W Solar) 12V/24V Auto | eBay (http://www.ebay.co.uk/itm/800W-Wind-Solar-Hybrid-Mppt-Controller-600W-Wind-300W-Solar-12V-24V-Auto-/290804210263?pt=LH_DefaultDomain_0&hash=item43b5481a57)

It looks like at least some support having a lower voltage (http://www.solarpaneltalk.com/showthread.php?7141-24V-Panels-and-12V-Battery) battery, but I'd want to be sure before connecting it up...

blackburn mark
08-11-2012, 10:34 PM
yep, it looks identical to that one... mine stated 200W for solar, 38v for 12v charging and 46v for 24v charging... my thinking was seeing a real 250 watts from a 250w panel would be pretty rare in this country and on the occasion that it did it would just be wasted... wouldn't make it to the battery through this charger ?

I might have bought a lemon with this... it didn't come with any instructions at all and the menu isn't very logical
you win some and you bin some :)

Jonathan
08-11-2012, 10:43 PM
46v for 24v charging

A nominally 24V (72 cell) panel can output close to 46Voc in bright sunlight, so the controller would have to drop the voltage from around that to about(!) 10.5-15V. It depends on how they've designed the converter...


... my thinking was seeing a real 250 watts from a 250w panel would be pretty rare in this country and on the occasion that it did it would just be wasted... wouldn't make it to the battery through this charger ?

The controller will either overheat and cut-out, or if it has a few more brain cells it will regulate the power input to only what it is rated for, so 200W. Solar panels are rated at an irradiance of 1000W/m^2, which is typical in England in the summer.


you win some and you bin some :)

Well let me know if you bin it ;)

blackburn mark
08-11-2012, 11:02 PM
Well let me know if you bin it ;)

ha!... it'll probably smell of burned Bakelite by then :)

m_c
09-11-2012, 02:16 AM
I did just type a big response, but just hit the wrong button, so here's just the summary!

Running a full split charge system will not cost you much on terms of fuel.
Even relying on the vehicle to fully charge the Aux batteries from totally flat, and assuming poor engine and alternator efficiency, will only take around a litre of diesel in addition to what you're taking to drive around. If you use the wind/solar to provide a continual charge, then the vehicle will not see that much of an increased load. Even if the batteries add an additional continual 20A load, it's only an additional 100ml of diesel an hour needed.

As for what split charge system to use, I'd personally build one using a large relay (200A range), and an Arduino.
Programme it so it monitors the vehicle battery, when it hits a set voltage, it connects the relay, if the vehicle voltage then drops too much, have it drop-out until the vehicle voltage recovers then add an additional time delay (will stop the relay continually switching in a short time frame, and give the alternator a rest instead of hammering it continually), and repeat until voltages stabilise. You could also programme it so it doesn't charge the Aux if the Aux batteries are above a set voltage.
That way you should get a reliable system, without the issues with conventional relay systems, and without the over-priced 'smart' systems.


Alsom, if you're van is only putting out 13.5V, then it has issues. It should be above 14V. Is it an old D, or a newer CDI?

blackburn mark
09-11-2012, 02:54 AM
I did just type a big response, but just hit the wrong button, so here's just the summary!
owch! i hate that

I am having second thoughts about my tactics (ish)
its an 08 CDI and I measured through the lighter socket with a cheap meter... ill take my fluke out tomorrow and see what It reads at some heavier terminals

I have been convinced that I should be pushing 14.8v into my auxiliaries for at least an hour after they stop drawing lots of current... if I can get anywhere near that out of my alternator ill go with a split and maybe boost the voltage a tad somehow....id have to manually isolate it though... and watch an amp meter for it to tail off... why is shit never easy ? LOL

m_c
09-11-2012, 12:21 PM
A CDI should get around 14.2V at the battery terminals after being running for a short period. If you're not, it's most likely the main positive loom has got corrosion in it at the starter terminal. Check to see if you're getting over 14.2V at the alternator, then check for volt drop between the battery positive and the alternator main output.
You can either remove the loom, drill two holes in line with the end of the cables and using a blow lamp/oxy-acy torch run plenty solder through the crimps, or just get a new loom.


14.8V?
That's really only needed if you're bulk charging the batteries after they've been run down. And to acheive that voltage on that much capacity, will take a lot of current!
Provided the solar is doing a good job of reguarly keeping the batteries around 13.2-13.5V, the continual trickle charge should keep them conditioned.


You're not using AGM batteries are you?
If you are, then you'll need some way of limiting current when charging, otherwise they'll pull every last bit of power from the vehicle they can when charging. They absorb charge far quicker than conventional lead acid batteries, and the voltage doesn't rise until they've got that charge.
We maintain some vehicles that have had AGMs fitted on the vehicle, and I've seen a flat one sit pulling 20A from a battery charger for 30minutes before the voltage even creeped above 12V, and if you jump start one, you can hear the load on the alternator and the voltage gradually creeps up.

blackburn mark
10-11-2012, 02:04 PM
morning MC... i wasnt going out in that rain yesterday!!... the battery is showing 12.3v before startup so i think that is on its way out (the little indicator on the battery is confirms this)

its showing 14.23v when its running, thats stable even if i increase revs, this has me thinking that maybe the van would push it at more like 14.4v and the tired battery is pulling it down ? ill look into this.

im looking to put standard wet batteries in, they sell as deap cycle 125ah but im guessing they are just re labled as such (ebay...love it)
iv taken the advice that the cheaper the better... with good charge control should last quite well... nothing like AGM's and the like but they really are a tad pricey

iv done a bit of research on the voltage issue, an article by a guy who has lived in his van for 8 years (and never used a genny) is charging at the much higher voltages, holding that voltage at least an hour passed the usual current drop (tempriture compensated)

i think most charge solar/wind controllers and car/van charge systems aire on the safe side (totally understandable...zero maintainence)
so i really want to hang on to the option to push the volage up should the need arise

i think the world is split on the issue of charge voltages for standard wet lead... i think having voltage options a hydrometer and a pen and paper might be the way to go :)

m_c
11-11-2012, 01:20 AM
14.2V is about as good as you'll get at the battery. I work on sprinters with 150A alternators (standard is 120A), and even after sitting running for a couple hours, they'll still be around 14.2V. Even with a brand new loom, there is always a bit of voltage drop between the alternator and battery.

A bad battery will not pull the alternator voltage down, unless a cell has gone short circuit, which means it'll get warm very quickly, and gas lots. A bad battery is more likely to go high resistance, which means it's actually easier for the alternator to hold the regulated voltage.

Deep cycle batteries do have a different internal construction. Normal starting batteries are designed to output high currents, with the trade of being they're not as good at prolonged drains or being run flat for extended periods of time, whereas deep cycle are designed to handle lower currents, and have better recovery from being left discharged.

blackburn mark
11-11-2012, 02:05 AM
I work on sprinters
splendid :) i know who to hassle if i get stuck... you dont use the star software do you :)


Deep cycle batteries do have a different internal construction.

i was assuming the worst with buying from ebay

Lee Roberts
11-11-2012, 05:14 PM
sooo... if the shit hits the fan at work and we all get laid off ill park up on the west coast of Scotland put a wind genny up and run my cnc once a week for my beans on toast :)

lol :triumphant: