Trying to charge batteries with bridge rectifier. No luck

Thread Starter

Ghandaffo

Joined Sep 29, 2019
5
Hello. I am working on an RV with solar panels and a 60A solar charge controller. Unfortunately the charge controller only works with solar panels and has no input for line power to charge the battery bank. No problem I thought. I got a 300A bridge rectifier, hooked it up to the solar charge controller in the attempt to trick it thinking there are solar panels feeding it. The charge controller accepts up to 150V DC so I should be fine there. Also the controller limits battery charge to 60A. When I the rectifier into the outlet, it works for about 2 seconds. The charge controller shows the voltage and sends 60A to the batteries. - Then the breaker blows. Obviously, the rectifier is drawing too much power. But why? if the controller sends 60A @ 14V to the batteries, at 115V that's only 7.3A (It is an MPPT controller which converts voltage to current with 95% efficiency). Why is the rectifier drawing much more and how could I limit the current (if my controller apparently fails at doing so)?

Thank you for your opinions
 

dendad

Joined Feb 20, 2016
3,006
I hope you are not just rectifying the mains direct into the solar charge controller!
Very dangerous!!

Why not just buy a battery charger?
That will be a lot safer.
 

debe

Joined Sep 21, 2010
1,141
Solar regulators are designed to only use solar input as its limited to the panel out put. If you feed 110V DC from the mains you will over load the regulator as the mains is capable of supplying too mutch current. Im suprised you havent destroyed the Solar regulator.
 

Thread Starter

Ghandaffo

Joined Sep 29, 2019
5
Yes, I am doing just that: feeding rectified mains into charge controller. Why is it dangerous? And why would I fry the controller? THe controller is made to regulate current and voltage. It works fine with my 3000W solar panel array. If the bridge rectifier puts out too much current the controller cannot handle (I wouldnt understand why) what would be a simple way to limit the current from the bridge rectifier? thank you
 

crutschow

Joined Mar 14, 2008
23,347
I am doing just that: feeding rectified mains into charge controller. Why is it dangerous?
It's dangerous if the charger input circuit is not fully isolated from ground and the output.

But I see no reason to limit the input current as the charger should automatically do that.
 

TeeKay6

Joined Apr 20, 2019
382
Hello. I am working on an RV with solar panels and a 60A solar charge controller. Unfortunately the charge controller only works with solar panels and has no input for line power to charge the battery bank. No problem I thought. I got a 300A bridge rectifier, hooked it up to the solar charge controller in the attempt to trick it thinking there are solar panels feeding it. The charge controller accepts up to 150V DC so I should be fine there. Also the controller limits battery charge to 60A. When I the rectifier into the outlet, it works for about 2 seconds. The charge controller shows the voltage and sends 60A to the batteries. - Then the breaker blows. Obviously, the rectifier is drawing too much power. But why? if the controller sends 60A @ 14V to the batteries, at 115V that's only 7.3A (It is an MPPT controller which converts voltage to current with 95% efficiency). Why is the rectifier drawing much more and how could I limit the current (if my controller apparently fails at doing so)?

Thank you for your opinions
@Ghandaffo
You say "The charge controller accepts up to 150V DC so I should be fine there." What is the RMS value of the mains voltage? Are you sure that simply rectifying that does not produce a peak voltage above the 150VDC rating? In addition, simple rectification without substantial filtering produces a pulsating voltage that the control may not like. Solar panels do not produce 50/60Hz pulsating output.
 

Thread Starter

Ghandaffo

Joined Sep 29, 2019
5
Ok. With a capacitor to smooth out the ripple the voltage gets too high. I will buy a 2:1 transformer. But still - will my controller regulate the current or do I need a device which regulates the incoming current? I am just so confused why the 20A breaker tripped. thanks
 

TeeKay6

Joined Apr 20, 2019
382
Ok. With a capacitor to smooth out the ripple the voltage gets too high. I will buy a 2:1 transformer. But still - will my controller regulate the current or do I need a device which regulates the incoming current? I am just so confused why the 20A breaker tripped. thanks
@Ghandaffo
The controller you use was specifically designed to work from solar panels. Solar panels produce a slowly varying DC output--never producing pulses at the mains frequency. How can we possibly know what the controller will do when powered from pulsating power?...even power with a small, but significant amount of pulsing; I refer to rectified and filtered--but not regulated, nor filtered sufficiently to reduce the ripple to a tiny amount that the controller can tolerate. You mention that the controller is capable of MPPT operation; that implies that it can sense (and respond to) a tiny output change with a tiny change in loading of the panel. That tiny change in loading may well produce only a fraction of one volt change in panel output, but you intend to provide a "panel" that changes its output dramatically 50 or 60 times per second. The MPPT logic doesn't stand a chance of working correctly. The correct approach would be to use a battery charger--designed for the type batteries you are using--when your batteries need charging. If you intend to use the batteries as they charge, then the charger at the least would need to be overrated to handle both charging and supplying whatever load you connect to the battery.
 

MrChips

Joined Oct 2, 2009
19,275
Note that 120VAC will not be exactly 120VAC. It could be as high as 135VAC.
This is a RMS voltage.
When rectified, the peak DC voltage is 120 x 1.4 = 170V. This exceeds your rated max of 150VDC.

It would be simpler to just use a battery charger.
 
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