36V asl6.5 transformer mods

[wonka]

Reading another thread got me thinking...

If the PJ inverter will operate much more "clean" at 32V, but I have a 36V asl6.5 transformer, is there any reason I couldn't add a few more turns to my 240V secondary and then decrease the output of the inverter via the front panel adjustment?  I haven't done the math yet as to how much wire is actually required, but the way I have my transformer setup (external) it wouldn't be too difficult to add a few more wraps...  

[Sid Genetry Solar]

1 hour ago, wonka said:

Reading another thread got me thinking...

If the PJ inverter will operate much more "clean" at 32V, but I have a 36V asl6.5 transformer, is there any reason I couldn't add a few more turns to my 240V secondary and then decrease the output of the inverter via the front panel adjustment?  I haven't done the math yet as to how much wire is actually required, but the way I have my transformer setup (external) it wouldn't be too difficult to add a few more wraps...  

The inverter actually regulates from the output voltage, so even if you adjust the transformer ratio, the output voltage will (should!) remain the same.

What is worth keeping in mind is the required headroom for a pure sine output...in overly simplified math, you will need (transformer voltage * square root of (2)) in DC voltage in order to reach the top of a sine wave.  For 36v * 1.414 = 50.9v, not accounting for any other losses (transformer, wires, FETs).

It is easy to determine the number of turns required to adjust the voltage by a certain amount.  With the inverter running, set your meter for AC volts, put one meter probe through the center of the transformer core, and then short both meter probes together.  PJ transformers typically range from 0.7v - 1.5v.  This is the turns/volt; you can only adjust the voltage in multiples of this number.

[dickson]

If the PJ inverter will operate much more "clean" at 32V, but I have a 36V asl6.5 transformer, is there any reason I couldn't add a few more turns to my 240V secondary 

 

The  32vac  is the  primary input to the  transformer  and can not be  converted from  36vac  by  adding  winding to secondary  .    Adding  more  turns to the  secondary L2 is to increase the  voltage  to  match the  L1  ac voltage .    Powerjack  design  some  ASL6.5 transformer 30 vac  which is better  for  48v dc lithium  iron phosphate battery  and  now  the ASL6.5 is 36vac .    My   ASL9.0  36vac  is now  running  60v dc  lithium ion battery string  and  the sine wave is good  to  54 v dc  battery input .   36vac transformer  need higher dc battery input  voltage  to keep the pure sine wave  for inductive load .   16s  lithium ion at 66 vdc  make the transformer run hot  so the  max  is 62 vdc  for ASL9.0  transformer .   

[Sid Genetry Solar]

3 hours ago, dickson said:

The  32vac  is the  primary input to the  transformer  and can not be  converted from  36vac  by  adding  winding to secondary  .

Here I will disagree.  What is being changed is the transformer ratio, regardless of whether the turns are added to the secondary, or removed from the primary.

There is a difference however; adding more turns to the secondary uses more wire, which is why it generally isn't done.  It does decrease the turns/volt core voltage, which may hypothetically provide more safety range before core saturation (which is when FETs go kaboom.)

However, removing turns from the primary will increase the turns/volt (if driven to the same AC input voltage)...and if this exceeds the transformer core's saturation voltage, the no-load current will start to rise (as well as transformer heat), AND reduced efficiency.

 

3 hours ago, dickson said:

16s  lithium ion at 66 vdc  make the transformer run hot  so the  max  is 62 vdc  for ASL9.0  transformer .   

Betcha this is due to a lack of ferrite chokes on the transformer primary wires.  These chokes serve to absorb the 24KHz SPWM carrier, as it just gets "burned up" in the big transformer if not filtered out.  If the big transformer is getting the 24KHz SPWM carrier, it'll get hot.

In my experience, the more ferrite choke filtration on the transformer primary wires, the higher the DC input voltage you can run...without the no-load current going up excessively.  Conversely, the less the ferrite choke filtration on the transformer primary wires, the sooner you'll notice high no-load currents & heat.

PJ seems to provide one ferrite choke on their inverters...and always with just a single turn of transformer primary wire through it.  In my experience, the best performance is found with 2 full turns of transformer primary wire through the ferrite.  Adding a second ferrite choke to the other transformer primary leg (with 2 turns) helps with higher battery voltages.

[dickson]

 What is being changed is the transformer ratio, regardless of whether the turns are added to the secondary, or removed from the primary.

 

I  do not know how to  change  a  36vac powerjack transformer  to a  32vac transformer like the GS  32vac transformer .   I   think a  36vac  transformer is design  that way  and  need  to  change the  primary  winding   and  secondary winding  according to a  formula  to  make it into a  32vac  transformer .   That is a lot  of  work  to rewind  a new transformer .  Powerjack  transformer  for  L1  N  L2  is  a  design  problem and not easy  to fix .  

[Sid Genetry Solar]

6 hours ago, dickson said:

I  do not know how to  change  a  36vac powerjack transformer  to a  32vac transformer like the GS  32vac transformer .   I   think a  36vac  transformer is design  that way  and  need  to  change the  primary  winding   and  secondary winding  according to a  formula  to  make it into a  32vac  transformer .   That is a lot  of  work  to rewind  a new transformer .  Powerjack  transformer  for  L1  N  L2  is  a  design  problem and not easy  to fix .  

Easiest way to change a PJ transformer spec from 36v to 32v...is to remove several turns of wire from the primary winding (which is on the outside anyway).  Having a variac on your bench is extremely handy for working with transformers.  There is no need to adjust the secondary winding.

The number of turns on the secondary winding is dependent on the turns/volt, which is dependent on the core.  Secondary imbalance is due to the winding specification not being matched; adding a few turns to the "low" coil is relatively trivial.

 

HOWEVER: It is worth noting that reducing the primary voltage specification on a PJ transformer, begins to run the risk of saturating the core with huge surge loads.  If the core saturates, the FETs go.  This is probably part of why PJ runs a rather high transformer ratio to begin with, as it reduces the risk of transformer core saturation at lower battery nominal voltages.

[dickson]

It is worth noting that reducing the primary voltage specification on a PJ transformer, begins to run the risk of saturating the core with huge surge loads

 

Will  your  GS inverter  with  32vac primary transformer   still have a pure sine  wave  when  battery voltage drop  to  45v dc  ?   The  GS inverter  seem to be able to  run  at  66v dc battery voltage  also .    Changing  powerjack  transformer primary input to  32vac  will  probably  not  make much  different  because  it is design  different  from the GS  transformer  .   I  have a variac  but  probably  not  going to  modify  the powerjack  transformer .  Adding  the  choke is very   useful  .   Thank you .  

[Sid Genetry Solar]

2 minutes ago, dickson said:

Will  your  GS inverter  with  32vac primary transformer   still have a pure sine  wave  when  battery voltage drop  to  45v dc  ?

At no load, 45.25v is the theoretical minimum for a pure sine wave, yes.  Under load, this minimum voltage requirement will rise.

 

2 minutes ago, dickson said:

The  GS inverter  seem to be able to  run  at  66v dc battery voltage  also

Yes, because of the dual ferrite chokes on the transformer primary lines.  Otherwise it'd start to struggle pretty badly up there.