solarseller.com alternative energy by John Drake Services, Inc. | home
5 Photovoltaics,Batteries, Cable and Wire 7 48 volt D.C. fluorescent lights 8 Low Voltage DC Lights Glossary of Alternative Energy Terms CHARGE CONTROLLERS 36 Solar Converters Special Solar and Battery Charging Equipment 37 TriMetric Battery System Monitors and Deltec Co. shunts 38 Timers,Linear Current Boosters,Photoswitch,Voltage Controlled Switches 39 Battery Desulphator by Solar Converters, Inc. 42 QuickCable links to instock products 48 DC Fuses, Holders & Fuse Blocks 56 Special Order Lenses for Thin-Lite Fluorescent Lights 57 Thin-Lite Special Order replacement ballasts 58 Special Order Lenses for Thin-Lite LED Lights BATTERY POST & TERMINAL CONNECTIONS, ADAPTERS AND BATTERY ACCESSORIES 62 Heat Shrink Tubing & Cable Lugs by QuickCable 67 Anderson SB Connectors 72 Iota Engineering Battery Chargers / Converters 73 SAE Connectors, Plugs, Sockets & Cords 75 DC to DC Voltage Converters & Dimmers by Solar Converters 76 Universal Generator Starter switch by Solar Converters 79 Thin-Lite Ballast Wiring Layouts 81 TriMetric 2030 and SC-2030 Wiring Layout
At the bottom of this page is a list of page links to every page in our website.
53 Diodes - Blocking & Bypass, What do they do?
We have been asked many times what is the difference between
a blocking diode and a bypass diode.
Let's try to straighten it out.
If a photovoltaic module is directly connected to a battery and a
blocking diode is not in the module or the controller, it will backfeed
power from the battery to the pv module at night.
In the early eighties, Solarex connected some pv modules to batteries
without blocking diodes and photographed them at night using light
A glow could be seen on the edges of each pv cell in the module.
Early pv charge controllers were either on/off or shunt type.
At night, when the battery voltage dropped, the controller would
re-connect the pv modules to the batteries(s).
This would allow the pv modules to drain power from the batteries.
In this case a blocking diode, a one-way gate, would be used between
the pv modules and the charge controller.
Later pv charge controllers had either a blocking diode built-in or
disconnected the pv module's, when their voltage dropped below that of the
batteries - as in night time hours.
Most current production pv charge controllers do not need a blocking
diode in the system.
A notable exception would be the Flexcharge NC25 and NCHC controllers
which do need a blocking diode.
These are hybrid controllers which can accept solar, wind, hydro or a
combination of power inputs.
In this case, a blocking diode is needed on the pv modules to prevent
night time battery drain as well as to protect them from voltage spikes
when another incoming power source is in the system.
Do your pv modules have a built-in blocking diode.
You can connect the pv module to a battery, I would recommend fusing
the positive side for safety, at night and cover the module.
Using a sensitive amp meter, check for reverse flow of current.
If none shows, your module has a blocking diode in it.
When purchasing a blocking diode you will want to look for the
low forward voltage drop (voltage is lost passing through a diode)
amp rating of the total pv module(s) plus 25%
maximum voltage rating of the open circuit rating of the pv modules
(Voc) plus 25%
Bypass diodes are located in the pv module itself - usually in the
"J" (junction) box.
Sometimes pv modules are wired in series to add up the voltage.
This is often seen when using an MPPT charge controller to take
a high voltage pv array located some distance from the battery
bank and drop it to the normal charging voltage.
When you see a pv module that is UL Listed and has a high system
series voltage, usually 600 volts d.c., it has a bypass diode in it.
If one or more pv modules is shaded in a series string of modules,
the unshaded modules can direct their power to the shaded
This can be destructive to the shaded modules as well as present
a fire hazard.
When a module has a bypass diode in it the diode is parallel to
the module output.
Since the diode has a higher electrical resistance than the cells in
the module, when the module is producing power the diode does
When the module is shaded the cell resistance goes up higher than
the bypass diodes' resistance.
Power from the other modules in the series string passes through the
diode without back-feeding into the cells of the shaded module.
1 Site Search - Quick Index | 2 The Realities of Purchasing On-Line | 3 Why Do Business With Us? | 4 Distributor of IOTA Engineering, Quick Cable and Thin-Lite products | 5 Photovoltaics,Batteries, Cable and Wire | 6 Lumen Outputs of Compact Fluorescent and Incandescent Lights | 7 48 volt D.C. fluorescent lights | 8 Low Voltage DC Lights | 9 Why buy Thin-Lite lights? | 10 Thin-Lite Emergency Survival Disaster LED lights | 11 Bogart Engineering Trimetric and Charge Controller Packages | 12 Educational Pages On This Site. | 13 Balanced Battery Charging and Dis-Charging by IOTA | 14 Portable & Emergency Fluorescent Light by Flexcharge | 15 DC Fluorescent Inverter Ballasts by IOTA Engineering and Montana Light | 16 Charge Controller Musings | 17 Bogart Engineering SC-2030 Solar Charge Controller | 18 PV Solar charge controllers with night lighting load by Flexcharge | 19 Thinlite Indoor Fluorescent Lights | 19 A - LED Lighting by Thin-Lite | 20 Thinlite Outdoor Lights | 21 Thinlite Replacement Ballasts | 22 Thinlite Replacement Lens - Diffusers | 23 Thinlite DC Lighting Products | 24 DC Lighting | Glossary of Alternative Energy Terms | 25 Parallel and Series Battery Bank Information | 26 What we sell and why. | 27 Amps Volts and Watts | CHARGE CONTROLLERS | 28 Emergency and Disaster Preparedness Notes | 29 Photovoltaic Module & System Wiring - Setting Up A PV System | 30 Wind - Hydro - Solar Charge Controllers by Flexcharge | 31 Water and Air Heating Diversion Loads for Charge Controllers | 32 Maximum Power Point Tracking Solar Charge Controllers by Solar Converters | 33 Solar Converters, Inc. Charge & Lighting Controllers | 34 SES Flexcharge Solar Single or Dual Battery Charge Controllers | 35 Thin-Lite ballast replacement installation guide | 36 Solar Converters Special Solar and Battery Charging Equipment | 37 TriMetric Battery System Monitors and Deltec Co. shunts | 38 Timers,Linear Current Boosters,Photoswitch,Voltage Controlled Switches | 39 Battery Desulphator by Solar Converters, Inc. | 40 Solar Converters, Inc. Products | 41 SES Flexcharge Products | 42 QuickCable links to instock products | 43 Thin-Lite products we stock | 44 DC Fuse & Circuit Breaker Types & Installation | 45 Switches - DC rated wall switches | 46 IOTA Engineering IQ4 Smart Charge Controller Owners Manual | 47 Our own alternative energy systems | 48 DC Fuses, Holders & Fuse Blocks | 49 Class T- DC Fuses & Fuse Blocks | 50 ANN - ANL - CNL DC Fuses & Fuse Blocks | 51 Inverter Cable and Overcurrent Protection Guide | 52 Installation and trouble shooting low voltage d.c. lighting | 53 Diodes - Blocking & Bypass, What do they do? | 54 Low Voltage D.C. Lighting Tips | 55 Your On-Line Privacy | 56 Special Order Lenses for Thin-Lite Fluorescent Lights | 57 Thin-Lite Special Order replacement ballasts | 58 Special Order Lenses for Thin-Lite LED Lights | BATTERY POST & TERMINAL CONNECTIONS, ADAPTERS AND BATTERY ACCESSORIES | 59 Battery Post Marine Conversions & Terminal Extensions | 60 Battery Post Connectors Conversions Adapters Repair | 61 Battery Terminal & Post - Cable Lug Covers & Protectors | 62 Heat Shrink Tubing & Cable Lugs by QuickCable | 63 Cable Lugs - Compression Connectors - No Crimping & No Soldering | 64 Heavy Duty Cast Copper Connectors - Lugs | 65 Cable Lugs - Copper Connectors - by Quick Cable - MAX | 66 Cable Lugs - Magna Lug Heavy Duty & Fusion by QuickCable | 67 Anderson SB Connectors | 68 Anderson SB Connector Accessories | 69 Solar Converters Special Order Items | 70 Thin-Lite LED and Fluorescent Comparisons | 71 Overview of Our Photovoltaic Systems | 72 Iota Engineering Battery Chargers / Converters | 73 SAE Connectors, Plugs, Sockets & Cords | 74 IOTA Engineering inverter ballasts | 75 DC to DC Voltage Converters & Dimmers by Solar Converters | 76 Universal Generator Starter switch by Solar Converters | 77 Stranded vs Solid Wire in low voltage systems | 78 IOTA Engineering Power and Lighting products | 79 Thin-Lite Ballast Wiring Layouts | 80 Wire & Cable Gauges and Information | 81 TriMetric 2030 and SC-2030 Wiring Layout | 82 DC to DC Voltage Converters | 83 TriMetric 2030 Battery Monitor Features | 84 IOTA Engineering DLS Battery Charger Features | 85 Lighting Systems | 86 Practical Alternative Energy Applications | 87 Portable and Emergency Power Systems | 88 Custom Cables | 89 Thin-Lite Special Order Fluorescent Models & Pricing | 90 Resources for Disaster & Emergency Preparedness | 91 Thin-Lite Special Order LED Light Models & Pricing | 93 My solar / photovoltaic history | 94 Battery Wiring Diagrams | 95 Battery Condition and State of Charge Charts | 96 Order Form | 97 Backup Power? | 98 Energy Expectations | 99 Power Needs Worksheet | 100 Efficiency | 101 Wire Loss Chart | 102 Solar Insolation Map / Chart | 103 SAE Connector Selection | 104 About Us | 105 Statement of Policy & Warranty/Returns | Contact Us | MPPT Charge Controllers - FAQ | Battery Equalizer/DC Autotransformers - FAQ | Constant Voltage Pump Drivers - FAQ | Linear Current Boosters - FAQ | Information | 1 | 2 | 3 | 4 | 5 | 6 | 7 | How To Videos and Reference by Quick Cable | Home Power Articles | R | P | A | B | C | D