Powerstar W7 Inverter modification

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Re: Powerstar W7 Inverter modification

Postby Jimbo007 » Tue May 16, 2017 11:21 pm

absolutely.
I know exactly what you mean having aquired my ham radiio licence some forty years ago in the days before the existence of multiple choice and building devices for about 55 years.
I built my first inverter some forty years ago and it was based on an Electronics Australia design. purely linear, no HF stuff there.
Prior to that, inverters were devices to generate high voltages for valve HT supplies, the earliest using 150 hz vibrators.
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Re: Powerstar W7 Inverter modification

Postby Graham_West_Wyalong » Wed May 17, 2017 6:42 am

Thanks for the post yunak, ok sounds likely hat you have some rudimentary component failure or as Jimbo said a slightly fried bit of software!

I do not know where the voltage sensing is done but I imagine it will be using a divider network and with my extremely limited hardware knowledge I woul imagine a capacitor drifting could cause the divider to fail.

I do prefer resistor divider networks. They are mathematically so much easier.

Where you would find it I am afraid you need to speak to some of the original blokes who got hold of the diagrams.

Short of that, replacing all electrolytics and any warmed up others on the control board may yield results.

I guess I would just buy the replacement boards and go from there if it were me at this point.

Cheers.
G.
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Re: Powerstar W7 Inverter modification

Postby Jimbo007 » Wed May 17, 2017 10:16 am

Yunak,
I agree 100% with Graham.
Just replace both boards and be done with it.
you will be back in operation without potential further problems or brown pants moments.
cheers,
Jim.
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Re: Powerstar W7 Inverter modification

Postby davidg » Sat May 20, 2017 11:16 am

Graham_West_Wyalong wrote:I worked out that the minimum I would want on my system was parallel 400 amp fuses

Try using approiate HRC fuses they have a graph where they will operate indefinately, as the current goes up over a certain point, they have a time to "blowing" with a point where they "blow" basically instantly.

Let's say 400A is a spike current if so lets say that normal was less then say 200A max and 400A would only occur for less than 5 secs. In an HRC it's likely you would use a 250A HRC fuse which may blow almost instantly at say 600A or whatever the fuse graph would show.
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Re: Powerstar W7 Inverter modification

Postby Graham_West_Wyalong » Sat May 20, 2017 2:29 pm

Ok I might look to see if they have 1000 amp ones. The reason I used the parallel 400s is that I could get them second hand fairly cheap!
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Re: Powerstar W7 Inverter modification

Postby davidg » Sat May 20, 2017 6:22 pm

Graham_West_Wyalong wrote:Ok I might look to see if they have 1000 amp ones.

How much continuous current are you drawing and how much peak current? 1000A is huge. :shock:

Typically from batteries almost any type, you try and keep the current under 250A as a maximum continuous draw otherwise cable sizes get really big and losses add up really fast at those sort current continuous currents.

Even at LV voltages currents are attempted to be kept at or below 250A per phase on a common substation, once they get to that sort of continuous current draw they generally want to install your own substation, to reduce grid losses and for efficiency.
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Re: Powerstar W7 Inverter modification

Postby Graham_West_Wyalong » Sat May 20, 2017 11:02 pm

Have sat on 6kva at the plug for some time in the past....

Assuming 75% chemical to electrical efficiency.

Allowing for voltage drop across the 300mm of 95mm cable and he inherent drop in deliverable voltage from the battery under this load I would not be overly surprised to hit 900 on a big surge.

I think the maths puts this around 3-400 with no startups.

I cannot see the point in designing a system to "just cope" when a few extra bucks will give heaps of latitude.

I see a fuse as something that will pop when you get a massive short and a circuit breaker to handle the overload situation.

Could be overkill but I have never had a problem with capability using this model!

I have 95mm battery cables btw!
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Re: Powerstar W7 Inverter modification

Postby davidg » Sun May 21, 2017 1:00 am

Graham_West_Wyalong wrote:I have 95mm battery cables btw!

Yes so does my system but it's based on 48V for the inverter, can deliver 18kW's for 30secs, 13kW's for 1 minute, 11.25kW's for 30mins, 8kW's for an hour and 7.5kW's indefinitely or as long as the batteries can deliver it. the fuses are 250A HRC, which is correct for the job.

The loss on the cables at the higher currents can reach 30 or so watts, the inverter system can measure the loss on the battery cable which is handy.

The battery interconnects are 640mm2 to reduce loss within the battery bank/pack.
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Re: Powerstar W7 Inverter modification

Postby Graham_West_Wyalong » Sun May 21, 2017 6:35 am

Nice setup davidg.

Mine is based on one 48v and three 24v salvaged forklift packs.

The interconnects are standard lead inters, about an inch by a quarter of an inch so 6x25 about 150mm2 the weak link is the cable at 95 as we are on 24volt our currents are doubled that of a 48v setup.

Anyway, it semestre to be working fairly well and i am not complaining.

I think this discussion started when I suggested the other chap should use ample fusing. I concede to your superior knowledge on the subject. (Esp as my fuses are simple load blow fast fuses) I think? Maybe I should check that.

Cheers. G.

Edit...... Hmmmmmm the fuses I scored are bussmann Fwh-400a they are rated ac/DC and fast blow 400 amps,

Are you suggesting that these fuses might be inappropriate for the job?
My mind worked on the simple calculation of what I expect to draw maximum rounded up to a neat muber!

Hehehehe just looked them up, maybe a bit of overkill. Still they should blow on a dead short.... Designed to handle some serious grunt but they are fast blow fuses (ac/dc).. I figured the blow was pretty quick on hitting the limit. I guess they are only $10 each might do a "spark" test see if one trips....
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Re: Powerstar W7 Inverter modification

Postby Jimbo007 » Sun May 21, 2017 9:33 pm

Graham'
the thought of you doing a "spark test" on a 400 amp fuse worries me a little as at 24 volts you will be playing with a 10 Kwatt arc and at 48 volts would be a 20 Kwatt plus arc. These are scarey power levels and will most likely result in your points of contact welding together.
Could you just simply remove one from your inverter leaving a single 400 amp fuse and load up the inverter to induce a fuse failure.
I think this would be much safer than having molten copper flying everywhere.
We would hate to lose such a valuable contributor through a moments hazardous experimentation !
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