completelycharged
Active member
- Joined
- Mar 7, 2018
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After buying various inverter options I'm now opting for the monty python option of "and now for something completely different"
My plan now is to go non conventional, mixing commercial distribution transformer oil cooling with off the shelf parts and hopefully not create a glorified deep fat chip fryer.
Basic plan, 5kVA toroidal transformer, inverter board and about a gallon or so of whatever oil is knocking around at the time (less water).
Once tuned, hopefully with no load power use 40W or less and with the oil cooling I should be able to run the output at around 6-7kW for around 10 minutes or so providing the FET's are all ok. The following posts will be the progress so far....
First up and main issue the actual inverter board to use and the first selection criteria is it must be low frequency H-Bridge.
Not H-Bridge - might be good for 5000W at 48V but I can't charge my battery through it. Forgot to add the reason for H-Bridge is so that I can push power back from wind and solar grid-tie inverters back through the inverter to charge the battery..
H-Bridge and lovely Chinese writing to follow (must learn Chinese some day). BUT this unit only has 4 FET's per active leg, so the 6000W rating (special Chinese factory rating) of this unit at 48V would mean each FET is dealing with 31A (averaeg not peak switching amps) each.
Now this is starting to look better, 6 FET's per leg (12 x 2) and 5000W "rated" at 48V using RIFB4710 FET's, which are rated at 75A and have a gate resistance of 11mOhm. Not ideal, but a good start. Still, that 5000W at 48V spread across 6 FETs then drops to 17A per FET. Surge current per FET of 70% would then be 15.1kW. Hmmmm...
The layout of the PCB, however, may not be able to spread out the current effectively between the FET's due to the traces though.... without modification or additional "helper" wires...
Another board indicates that it can handle 7500W at 48V with 5 FET's and a surge capacity of 21000VA.... hmmm.. thats 21000/48 = 438A over 5 FET's = 88A per FET. Even the 7500W rating is 31A per FET.
The FET's indicated are either HY4008 or HY3810 and from the non specific indication of a board sold as 24V, 48V and 60V the HY4008 at 80V rating is not going to go into a 60V board.
The HY4008 is rated at 200A and would be curious to see the legs of the TO-247 cope with 200A for a long period of time.... the HY4008 does, however have a Rds of only 2.9mOhm so way lower losses.
The H3810, which I'm guessing/hoping would be in the 48V unit is rated 100V and 180A with Rds of only 5mOhm, brilliant..... but....
Using the same PCB layout as the board with 6FET's per leg AND the board in the previous post actually shows the under side PCB trace of a different board altogether with 5FET's per leg !!!!!!!
The powerstar W7 3000W units use 6 FET's per leg and I know that these units can take some abuse, my older unit can start my 3hp circular saw and cope with it stalling with my poor method of cuttingpallets up, which jams the blade on the odd occasion..
The 6000W version, which incoporates two transformers in the case rather than a single larger transformer, still uses 6 FET's and is a proven inverter for abuse but not so great on no load power consumption due to the E type transformers lossy design.
So, this makes me think that the 6 FET board is the way to go (can't find any larger boards yet....) and it should be able to cope with 5000W continuous without any problem.
My plan now is to go non conventional, mixing commercial distribution transformer oil cooling with off the shelf parts and hopefully not create a glorified deep fat chip fryer.
Basic plan, 5kVA toroidal transformer, inverter board and about a gallon or so of whatever oil is knocking around at the time (less water).
Once tuned, hopefully with no load power use 40W or less and with the oil cooling I should be able to run the output at around 6-7kW for around 10 minutes or so providing the FET's are all ok. The following posts will be the progress so far....
First up and main issue the actual inverter board to use and the first selection criteria is it must be low frequency H-Bridge.
Not H-Bridge - might be good for 5000W at 48V but I can't charge my battery through it. Forgot to add the reason for H-Bridge is so that I can push power back from wind and solar grid-tie inverters back through the inverter to charge the battery..
H-Bridge and lovely Chinese writing to follow (must learn Chinese some day). BUT this unit only has 4 FET's per active leg, so the 6000W rating (special Chinese factory rating) of this unit at 48V would mean each FET is dealing with 31A (averaeg not peak switching amps) each.
Now this is starting to look better, 6 FET's per leg (12 x 2) and 5000W "rated" at 48V using RIFB4710 FET's, which are rated at 75A and have a gate resistance of 11mOhm. Not ideal, but a good start. Still, that 5000W at 48V spread across 6 FETs then drops to 17A per FET. Surge current per FET of 70% would then be 15.1kW. Hmmmm...
The layout of the PCB, however, may not be able to spread out the current effectively between the FET's due to the traces though.... without modification or additional "helper" wires...
Another board indicates that it can handle 7500W at 48V with 5 FET's and a surge capacity of 21000VA.... hmmm.. thats 21000/48 = 438A over 5 FET's = 88A per FET. Even the 7500W rating is 31A per FET.
The FET's indicated are either HY4008 or HY3810 and from the non specific indication of a board sold as 24V, 48V and 60V the HY4008 at 80V rating is not going to go into a 60V board.
The HY4008 is rated at 200A and would be curious to see the legs of the TO-247 cope with 200A for a long period of time.... the HY4008 does, however have a Rds of only 2.9mOhm so way lower losses.
The H3810, which I'm guessing/hoping would be in the 48V unit is rated 100V and 180A with Rds of only 5mOhm, brilliant..... but....
Using the same PCB layout as the board with 6FET's per leg AND the board in the previous post actually shows the under side PCB trace of a different board altogether with 5FET's per leg !!!!!!!
The powerstar W7 3000W units use 6 FET's per leg and I know that these units can take some abuse, my older unit can start my 3hp circular saw and cope with it stalling with my poor method of cuttingpallets up, which jams the blade on the odd occasion..
The 6000W version, which incoporates two transformers in the case rather than a single larger transformer, still uses 6 FET's and is a proven inverter for abuse but not so great on no load power consumption due to the E type transformers lossy design.
So, this makes me think that the 6 FET board is the way to go (can't find any larger boards yet....) and it should be able to cope with 5000W continuous without any problem.