running 12vsmart chargers in parallel

[T1 Terry]

Interesting, thanks for that John. My only experience to date has been DC to DC usin an inverter and mains charger, never a purpose built DC To DC charger but I can see how the circuitry could be similar on the output stage. I wonder if multi stage mains chargers suffer the same problems? I have a few C Tek chargers here, for various reasons, so I'll try an experiment and see what happens. The $99 2 stage evil bay 40 amp charger isn't effected

T1 Terry

[sunnykids]

Has anyone had any experience with these evil bay 40a 3 stage chargers ? They seem reasonably priced ?

http://www.ebay.com.au/itm/40-Amp-Batte ... 082wt_1393

I think a relay to isolate the chargers would be the solution. If the solar panels are providing more charge than the charger, I can only see the dc-dc charger being used when the panels are not charging.

[T1 Terry]

Don't ya just love their B/S sales talk They are only 2 stage chargers but they work fine, mine is over 2 yrs old now and had some serious punishment including melting a fuse and holder and a reverse connection blowing 2 x 50c diodes. They work well as they are for lead acid batteries but require an additional external fan for lithium batteries to prevent over heating. With a bit of minor internal dashpot adjustment they can be trimmed to suit any type battery as the end of boost/switch to float voltage can be adjusted. They have no problems running in parallel with a PWM solar regulator and combined with a 600W inverter wired through a VSR make a very good DC to DC charger at a much lower price and none of the annoying compatibility issues. With a bit of planning the inverter can do double duties and so can the charger. I bought mine through Oz Plaza but Bit Deals are also good people to deal with on evil bay.

[supersparky]

Has anyone had any experience with these evil bay 40a 3 stage chargers ? They seem reasonably priced ?

http://www.ebay.com.au/itm/40-Amp-Batte ... 082wt_1393

I think a relay to isolate the chargers would be the solution. If the solar panels are providing more charge than the charger, I can only see the dc-dc charger being used when the panels are not charging.

One of the guys at work had one charging lead/acids. He let the smoke out and got a replacement under warranty. The new one worked fine after we fitted a fan to keep it cool.
And thanks to this post I think I have worked out what the relay that goes nowhere in my setup was originally installed for. I have been trying to figure out why sometimes solar wins and other times the 24-12 dc-dc charger wins. Now I have something else to check.

[John M]

[quote="sunnykids"
I think a relay to isolate the chargers would be the solution. If the solar panels are providing more charge than the charger, I can only see the dc-dc charger being used when the panels are not charging.[/quote]

I think a relay to isolate the chargers would be the solution. If the solar panels are providing more charge than the charger, I can only see the dc-dc charger being used when the panels are not charging.[/quote]
I have the DC Dc charger switched on via the ignition, it is used whenever the motor is going, usually only an hour or so every couple of days, I tried to keep an eye on the solar input whilst driving down the road but the input fluctuates so much with shade etc depending on where you are driving, so it seemed like the best way to set it up, the batteries get that quick boost (20a) when the motor is running, usually in the morning, and them it is left to the solar to manage them when we stop, the relay in the solar circuit uses the normally closed contacts (when the ignition is turned on the contacts open, so disconnecting the solar. and engaging the Dc Dc charger.

[oldtrack123]

Hi John
The meter fluctuating with shade indicated that the solar was working quite successfully
AND IS NO PROBLEM
A PWM reg , connected direct to the battery, has no problems coping with paralleled sources
The one with the highest output[load voltage] at any point in time will prevail[proven in real life]


However I do not suggest paralleling even two exact "similar"smart chargers unless the maker says it is OK

Peter

[John M]

Hi John
The meter fluctuating with shade indicated that the solar was working quite successfully
AND IS NO PROBLEM
A PWM reg , connected direct to the battery, has no problems coping with paralleled sources
The one with the highest output[load voltage] at any point in time will prevail[proven in real life]


However I do not suggest paralleling even two exact "similar"smart chargers unless the maker says it is OK

Peter

Hi Peter,
I was not concerned with the fluctuation in charging rate from the solar, I have an MPPT regulator, and despite contrary reports about MPPT, and the fact that I am now on my third one I am basically happy with my choice, the problem was with the incompatibility of the two chargers, solar and DCDC where one charger tended to cancel out the other, and nothing happened from either I believe each charger separately read the voltage and both went to float even though the batteries were below that voltage, since I fitted the relay both units appear to be working correctly.
I have 360w of solar (would have more except for the problem of space) I have never seen the theoretical maximum (my calculations 24A) but regularly get close on 20A from the solar before the batteries reach the stage where they wont accept that amount, In describing batteries and charging T1 very aptly likened them to filling glasses of water, I tend to think of them more likened to bottles where the restriction is also in the diameter of the neck, which tends to severely restrict the rate at which they can be filled. My original reason for fitting the DCDC charger was for those times when the batteries are undercharged, due to weather conditions etc, in which case I can charge the batteries while I drive.
I also have an inverter charger, and have been advised by the manufacturer that I require a minimum of a 5kw generator to run that, so I carry a home made motor driven battery charger, ie. a 30a alternator coupled to a 5hp motor, half the size and weight of a suitable 240v genny but for those times when I need to charge the batteries, a little noisy but effective, though probably not much noisier than a larger genny would be.

[oldtrack123]

Hi John
I believe I now what is happening
Both the Solar reg & the dc charger should be seeing [sensing ]the battery voltage
But IF the battery is near fully charged or in float mode ,the combined currents will give a rapid voltage rise leaing both to sense [wronly]that the battery is overcharging.
But that should only happen under THOSE conditions,UNLESS you have a high resistance connection somewhere in the charging circuit which could realy give such problems as one or both will be reciving a false voltage indication

While you have overcome the problem with the relay, you may not be using both to max capability especially if the batterries are in low SOC

Peter

[T1 Terry]

Peter,
I have the same MPPT controller as John has, even with the lithium batteries with their incredibly low internal resistance exactly the same thing would happen, the MPPT charger would sut down if it saw another charging source at the battery. The second problem with the MPPT controllers was they would not return to boost stage till they saw mid 12v readings or the solar was disconnected/reconnected, it just didn't play well with other charging sources. I trialed the 3 other MPPT controllers to see if was just a GSL problem but they all do the same thing.
Once the smoke came out of the last of them I put them all in the junk pile and put it down to experience. The mates bus with the Outback MX80, the Rolls Royce of MPPT controllers shuts down as soon as the Victron Quattro is switched to charger mode, he still has the exTelstra Yuassa 125Ah AGM's, 720Ah bank, it appears to be an MPPT control problem, just the way they do their thing of voltage sampling.

T1 Terry

[oldtrack123]

Hi Terry
OOPS, I made a bobo
My comments are relative to PWM regs
You are correct , I understand there could be problems with MPPT regs by the nature of their voltage sensing & load matching behaviour.
Peter