Shorted diodes & dead batteries?

arby · April 2012

Hello all, new here and an amateur at solar.
Over the last 3 or 4 years I have installed a system at my remote cabin.
4x130 watt Kyocera panels in series for 48 volts. An MX 60 CC, an Xantrex SW 5548 inverter , 8 x 6 volt Surrette 530 batteries. and 5500 watt Honda generator backup. Has been functioning well for the last two years.
My first visit in 2 months found dead batteries and non functioning inverter.
I got the inverter back up by separating the batteries and charging 12 volts at a time. Once I had close to 48 volts DC, the inverter began working again and was able to use it to charge the batteries further.
7 volts coming from panels. I went to the panels and opened the connection boxes and water dribbled out of two, and the bottom one appeared to be full of water.
Inside the boxes are 6 diodes and the soaked one had all of the diodes missing one pin end.
I am not sure what caused the missing pins but I assume the water caused a short and melted them off. I am going to try and find replacement diodes and see if replacing them fixes the array.
My main question is why did my batteries drop down to less than 10 volts for the 48 volt bank? ( not used except to search, and run my tri-metric.)
PS: I think my auto start generator may have been out of propane, but that doesn't explain the huge drop in the batteries.

Thanks

Cariboocoot · April 2012

Re: Shorted diodes & dead batteries?

Welcome to the forum.

It does sound like you had some serious panel problems. I think those K130's had barrel diodes, but if you can't find them there may be room for these TO-220 type: http://www.solar-electric.com/8ampbypdiod.html

Really you've got to determine how/why the water got in there or else ... Somehow the junction boxes lost their seal. Probably at the wire intrusion. Depending on how they're oriented, the wires can wick water right inside.

Batteries die. They'll do it with nothing drawing on them. Even if you had the inverter off, the Trimetric and MX60 are going to use power. Without charge going back in, the batteries will go down, down, down. This is not the first time I've come across 48 Volt battery bank turning into 10 Volt scrap metal. Those batteries may recover, but they are not going to be good and they are not going to last very long.

And while I'm heaping on the bad news ... a 520 Watt array isn't enough to charge 400 Amp hours of 48 Volt battery. Not by a long shot. You need about 2500 Watts for that much battery. You barely have enough panel there to stay ahead of self-discharge without any loads.

I'm going to suggest you re-think the whole system, starting with the load requirements.

BB. · April 2012

Re: Shorted diodes & dead batteries?

Our host sells some replacement diodes--if they will fit your application.

8 Amp Solar Panel Bypass Diode
Solar panel blocking diode, Schottky

The problem with accessible junction boxes is they are virtually impossible to seal. Generally, you need to have the wire come in the bottom and a "drip loop" (wire runs down to drain water before running backup up and over). Also, for many j-box installations, you should drill a small weep hole in the lowest corner to allow water to drain out (don't know if this would void the warranty on your solar panels or not).

I would worry that you will have problems getting the panels back to reliable condition--Is there any obvious staining/corrosion visible from the glass side of the panel around the J-box area? Placing the panels in full sun for a day (or several) with an open j-box to drive out any moisture.

Newer/larger panels are all using sealed junction boxes with attached leads + MC4 connectors. You can buy Male/Female MC4 jumper cables--cut in 1/2, plug into panel and wire cut ends into the balance of your system.

In general, flooded cell batteries need to be recharged every 1 month or they will self discharge too far and begin to sulfate and eventually fail. (older and fork lift type batteries will self discharge even faster).

It is possible that a bad connection or open cell in a battery string to prevent charging... And there is the old load left on (or inverter left on taking 30+ watts with no load) and the solar array not being able to keep up with the energy usage.

In general, my experience with a battery bank taken to dead (especially a bank with a few years on it) will eventually need to be replaced (days or weeks). If these are fork lift/traction batteries, it is possible that lots of charging/equalization may bring them back to a reasonable life.

Having a battery bank "killed" by some electrical failure (or genset out of fuel) is a huge problem with remote/unattended systems... I would like to use a Battery Monitor (Xantrex or Victron) that has an output contact that can be set to turn on an alarm or turn off the loads at a programmed setpoint (i.e., turn off loads at 50% or 20% state of charge). Much more accurate than using voltage based switches.

-Bill

niel · April 2012

Re: Shorted diodes & dead batteries?

it is unfortunate news for you i'm sure as you not only have damage to the pv you also have a great deal of capacity loss and possible damage to the battery bank. in the case of a junction box, it is sometimes wise to place a small weep hole around the lowest point of the j box so if such an occurrence happens it may also have a way out of the j box. this is not a guarantee that this won't happen as the hole can clog or freeze over so the precautions taken to keep the water out in the first place are important. if you are lucky enough that only the diodes need replacing you can count yourself as fortunate. as was mentioned, the pvs lack the ability to properly charge the battery bank, but can be adequate to give a float charge to maintain the batteries preventing them from being depleted due to self discharge and i suspect this was the purpose you had in mind for the pvs.

arby · April 2012

Re: Shorted diodes & dead batteries?

niel wrote: »

it is unfortunate news for you i'm sure as you not only have damage to the pv you also have a great deal of capacity loss and possible damage to the battery bank. in the case of a junction box, it is sometimes wise to place a small weep hole around the lowest point of the j box so if such an occurrence happens it may also have a way out of the j box. this is not a guarantee that this won't happen as the hole can clog or freeze over so the precautions taken to keep the water out in the first place are important. if you are lucky enough that only the diodes need replacing you can count yourself as fortunate. as was mentioned, the pvs lack the ability to properly charge the battery bank, but can be adequate to give a float charge to maintain the batteries preventing them from being depleted due to self discharge and i suspect this was the purpose you had in mind for the pvs.

Thanks for the replies guys.
I have 4 more 270 watt panels that I intend to install this summer. I had to go 48 volts because my panels are 55 meters from the batteries.
I have found the apparent equivalent diodes that are in the KC 130 panels. They are 1N5408.
I still wonder what killed the batteries. As far as I can tell, the search feature of the 5548 inverter uses .04 amps, and all that is left would be the Trimetric which appears to use milliamps, and the MX60, which I can't seem to find out.
Every so often these batteries have had a good charge from the genny at 50 amps or so.
Big learning curve here, but I am enjoying it.
Thanks

niel · April 2012

Re: Shorted diodes & dead batteries?

the batteries most likely died from your phantom loads you have going all of the time. any meters, controllers, etc will draw over several months, without a replenishing charge, enough to wipe your capacity.

westbranch · April 2012

Re: Shorted diodes & dead batteries?

Add to that the natural decay of FLAs, be it ever so small

Photowhit · April 2012

Re: Shorted diodes & dead batteries?

Not to mention your auto start genny repeatedly trying to start, heck that might even be a pass through/unprotected cuircut to ensure it starts after the inverter shuts down....

65DegN · April 2012

Re: Shorted diodes & dead batteries?

arby wrote: »

I had to go 48 volts because my panels are 55 meters from the batteries.

You really didn't have to go to 48V because of the distance between the batteries and panels. Using the MX60 panels may be put in series to go as high as 140V regardless of the battery voltage. However in my opinion 48V is a superior system voltage.

arby · April 2012

Re: Shorted diodes & dead batteries?

Just back from trip to cottage. I replaced the diodes, and all is working fine once more. I think that I found the culprit that killed the batteries. A BLS ( battery life saver) that was installed a few months previous. Since this equipment is connected directly to the battery bank at the posts, it does not shut down on a low battery. The battery bank held its charge for the past 3 weeks with zero input, so I am hoping the system is still fairly good.

waynefromnscanada · April 2012

Re: Shorted diodes & dead batteries?

arby wrote: »

I think that I found the culprit that killed the batteries. A BLS ( battery life saver) that was installed a few months previous.

Well obviously that was a properly named device! At least it was as far as making money for the snake-oil salesman was concerned. :grr
There are so many rip-offs out there, just waiting for some trusting, honest person to come along and be separated from their cash, it's not funny! :grr
End of rant.

Shorted diodes & dead batteries?

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Shorted diodes &amp; dead batteries?

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Shorted diodes & dead batteries?