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bridge rectifiers
By halfcrazy, Section Homebrewed Electricity Posted on Sun Feb 11, 2007 at 10:19:56 PM MST
what happens if

what happens when the rectifiers like the ones the dans sell fail can or will the ac flow through or do they just not have any output? and with a good heat sink how many amps would you feel safe running for say 3-4 hours continuis through the 35 amp ones they sell here? this may be a real odd idea but i was thinking of taking 120vac and send it through the rectifiers and into a spair mx60 would this work? seems like it has to as long as the rectifiers can handle the load?

bridge rectifiers | 25 comments (25 topical)

Re: bridge rectifiers (3.00 / 0) (#1)
by jimjjnn on Sun Feb 11, 2007 at 03:44:11 PM MST

Why would you want to run 120VDC to your MX60? There would be losses as well as I don't think the MX-60 can carry 120VDC anyway( I could be wrong ).
Denver,CO

Re: bridge rectifiers (3.00 / 0) (#2)
by halfcrazy on Sun Feb 11, 2007 at 03:54:51 PM MST

well the mx is good for 140 vdc. and what we have is a spare mx60 setting there and the problem we have is trying to get the ac either 120 or 240 from the generator to the 1000ah of 24 volt batterys the fx2024 we have there pre turbo just doesnt have enough umph to charge the batterys effectively cant equailize at all. but the 60-70 amps from the mx would do it if it doesnt pan out he may have to buy a second inverter but this would be a lot cheaper for him if it would

Re: bridge rectifiers (3.00 / 0) (#16)
by Volvo farmer on Mon Feb 12, 2007 at 04:13:06 AM MST

Something ain't right here. The FX2024 is rated to charge batteries at 55A DC, that's pretty close to the 60A you expect from the MX60. Do you have a "Mate" for that inverter? My VFX3524 came with the charge amps set really low from the factory. With a Mate, you can increase the charge amps so that it will charge at 50-55A DC. That should be plenty to equalize 1000Ahr 24V batteries. You'll need a big enough generator to be able to pull 16A or so out of one leg of it, unless you can rewire the generator for 120V. I'd imagine a 10KW unit might not mind an unbalanced load of 16A out of a single leg though.

Volvo Farmer

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#17)
by halfcrazy on Mon Feb 12, 2007 at 07:30:30 AM MST

yes we have the mate i need to do some more investigations on this system the customer doesnt have a amp hour meter. he has a 5000 watt honda with the switch to go straight 120 volts. maybe the inverter has a issue as we have split the bank in half and still cant get above high 28 volts maybe to like 29.4 if we let it run for like 8 hours even tried one day with 55 amps coming in from the pv array. i am starting to suspect maybe a issue with tempature compensation there is no hub but both mx and fx have rts's but they are both older models real low serial numbers maybe a call to outback is in store. as a side not i found a hobart battery charger for forklifts 24 volt 95 amp with manual equilization for 350 bucks plus shipping seems like the way to go rather then smoke my mx 60 for a friend???

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#18)
by Volvo farmer on Mon Feb 12, 2007 at 08:56:33 AM MST

I still say something is not right with the inverter/charger settings, or possibly the batteries are very low or damaged. Last night, after 2.5 days of clouds, I brought my 800Ahr (Surrette S530 X 8)battery bank from 25.0V to 29.4 in about one hour. Trimetric read about 60A DC charging. Solar was negligable.

If you have the Mate, you can see an AC->DC conversion amount on the screen but it doesn't have a great deal of resolution, I believe .1 or .2KW. Last night mine was sitting at 2.0 KW. In the absence of a amp hour meter, the Mate will at least tell you if you are utilizing the full available power from the generator. I'd imagine you want to see over 1.5KW on that screen while you are charging with the generator.

This perplexes me. Who would go out and spend $10,000 on a solar electric system and not spend $140 on a dang trimetric? If this guy is truly your friend, I'd get him to buy the trimetric before a forklift battery charger.

I truly believe you are barking up the wrong tree here. Ask any experienced installer if you should be able to Eq batteries at C/20 and I'd bet every one of them would say yes. If you add your 55A of solar to generator, you've got less C/10! I'm almost certain than anything faster than C/10 is not recommended by any battery manufacturer.

Volvo Farmer

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#21)
by halfcrazy on Mon Feb 12, 2007 at 05:31:03 PM MST

Volvo Farmer and others it seems there may be something amiss here the original installer of this system "not me" did the system he claimed no one needs an amp hour meter that the mx60 will tell you anything you want to know. so you can imagine what the rest of system looked like. so i have been trying to bring it back. the batterys 16 interstate 220ah 6v wired for 24 volt the original install had 8 of these right outside on the deck no insulation nothing then a year later added 8 more still right on the deck outside did i mention we are in maine -20F in the winter. so they stayed that way for i think 3 years then when i cam into picture we got them inside in a nice box on a concrete slab with radiant heat a steady 70 deg F. and they have been in for 2 years. i gave him a hydrometer but dont think he has checked the specific gravity? i did check with a voltmeter with everything unhooked and all batteries where the same like 6.2 volts. i have the fx charger set to 14 amps ac and still of yet have got him to spring for a amphour meter so no real acurate data also have 12 shell sq160 panels feeding 10 into a mx60 2 into a c60 so i really dont think it is a lack of power unless something is wrong? the inverter did spend the first 3 years of its life outside literally and no turbo fan so maybe damage is done inside it did start humming really loud about 6 months ago? i will try to get some specific gravity readings and try to get a estimate on charger output via mate and see could the batterys be really sulfated and cause these symtoms? oh the original installer said not to ever equilize it is bad for batteries so for the first 3 years there was never a attempt to equilize and the first 3 years there was only 2 of the shell panels on system so my guess is it was cronically undercharged not shure what to do about trying to really boil batteries maybe take over a spair sw4024 i have hear? or 16 new batteries?

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#22)
by TomW on Mon Feb 12, 2007 at 06:35:04 PM MST

crazy;

Well, do not mistake me for an expert. Personally, I think that 3 years outside with unknown and likely bad or no care, then 2 years inside you have 5 year old ill treated batteries and probably need to recycle those and grab something you can treat properly. Or you could try to revive them at unknown cost in time or materials and still end up replacing them. May depend on the required level of reliability and budget for the project.

It seems that to get long life [like ten years] from flooded batteries they need good care and luck.

Just an opinion.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#23)
by Volvo farmer on Mon Feb 12, 2007 at 09:10:25 PM MST

I'll admit, I am also no expert, but I spend my entire day diagnosing problems with mechanical devices and listening to people to try and figure out what went wrong.

From what I have heard from you, you have one of two problems... Either the batteries are damaged or the loads on the system are way out of proportion (too high) for what is being produced.

My neighbors astounded me. They got out here six years before I did and made sixteen Sam's club golf cart batteries (24V) last SEVEN years. The've got Satellite TV which they never shut off (with TIVo), use incandesant lamps in 50% of their fixtures, run a in-floor heat system with a 24V volt zone valve transformer on all winter long, etc.

Here's the kicker. They had 540W of solar on the roof and added 150W about two years ago. It wasn't cutting it so I convinced them to get more panels. They went for 460W of Evergreens.

So I go up on the roof to help wire this stuff up and the first thing I notice is the 150W of panels are wired for 12V on a 24V system... and the fuse is blown! 150W of power, wired in on the roof for two years... wasted. I guess my point is that people can be pretty oblivious to what is going on right under their noses.

I disagree with TomW that cold batteries are necessarily abused batteries. Mine spent all winter at 40-45F but I was only into them 10% daily. I think they suffered no harm. However, unaware people could murder cold batteries easilly. It appears that you are dealing with unaware people in this situation, certainly moving batteries to a warmer spot increases capacity, but without an Ahr meter, your friends are surely flying blind as to their daily intake vs output of electricity.

Volvo Farmer

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#24)
by halfcrazy on Tue Feb 13, 2007 at 04:28:33 AM MST

Thanks to all i am going to insst on a amphour meter and a day of proding around at there house the loads are high but shouldnt be to high they have a big outdoor boiler that has a 007 taco running at 100 watts 24/7 but i put an off and on timed relay 5 minutes on 25 off works like a charm and is wired in in such a way as if the heat comes on it overides it and stays on. and when the batterys where in the cold for years they where cronically undercharged i am shure of it. I will start a new post when i know more

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#3)
by fungus on Sun Feb 11, 2007 at 04:13:55 PM MST

Remember that the MX60 can only handle 140v DC and the peak of an AC wave is higher than that:
peak=1.4*rms
=1.4*120
=168v-over the max voltage. You could try varying the speed of the gen to get a lower voltage though.

'Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.'-Albert Einstein
Fungus - www.reenergy.co.uk

Re: bridge rectifiers (3.00 / 0) (#4)
by DanB on Sun Feb 11, 2007 at 04:22:39 PM MST

If it's a wind turbine - then you cannot run it through an MX60, it's not designed for that. The wind turbine must stay under load all the time - the MX60 will disconnect it from the load sometimes. Then the blades would overspeed and the wind turbine would be in peril and the MX60 would be confused I think.

Re: bridge rectifiers (3.00 / 0) (#6)
by halfcrazy on Sun Feb 11, 2007 at 04:24:48 PM MST

Dan it is a basic gas generator

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#7)
by DanB on Sun Feb 11, 2007 at 04:39:32 PM MST

interesting.
It might work fine!
I'd ask outback about that one... it'd be expensive smoke coming out if there was a problem.

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#8)
by halfcrazy on Sun Feb 11, 2007 at 04:44:01 PM MST

this is true about smoke. what would it take to make a dc unit like you and scott built that could do around 60-80 amps into a 24 volt bank? wonder about magnets and coils specifically figure it would take 7-8 hp in a gas engine maybe less?

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#5)
by halfcrazy on Sun Feb 11, 2007 at 04:23:57 PM MST

hadnt thought of that but easily adjustable. but my real question is can or will the rectifiers fail and pass ac thru to the dc terminals? i wonder about damage to the mx although if you built a turbine and rectified it into a mx you would be doing the same thing. maybe run the generator at half throttle we should be getting a decent voltage to run into the mx?

Re: bridge rectifiers (3.00 / 0) (#9)
by wpowokal on Sun Feb 11, 2007 at 04:57:13 PM MST

Just on the rectifier question I would alow 20 amps max/bridge with a large heatsink.

In my experience they most commonly fail open circuit, but may not.

allan down under
"Dream as if you'll live forever, live as if you'll die today." James Dean
[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#10)
by boB on Sun Feb 11, 2007 at 05:46:50 PM MST

My suggestion is to use a step-down transformer from the generator
output, then the bridge rectifier into the MX60, at a DC voltage just
somewhat higher than the nominal battery voltage, say, 50 Volts DC
for a 24Volt DC battery bank.
And even then, stick a fuse in series with the bridges positive output
and the MX60 PV input. Maybe a 15 or 20 Amp fast blow. Then, if the
bridge shorts, the FETs parallel diodes will conduct and blow the fuse.
A 200 Volt bridge should be fine for that stepped down AC voltage.

I wouldn't hesitate to apply 100 Volts DC to the MX60 input, but as I
told 1/2 Crazy, the MX60 doesn't have a real high PWM resolution at the
higher input voltages like 140 Volts DC. Also, the DC-DC converter will
be hotter with the higher input voltages. It's always best to start
with a lower input voltage if possible.

The MidNite Solar Classic will have better resolution at the higher
input voltages though.

boB
K7IQ

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#20)
by boB on Mon Feb 12, 2007 at 11:56:16 AM MST

Also, If you try this with an MX60, adjust the current limit
down to say, 30 Amps to start with to see how things go.

Then if all seems well, crank it up.

boB
K7IQ

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#11)
by Nando on Sun Feb 11, 2007 at 06:10:07 PM MST

Do not thread in areas of not knowledge.

A 35 amps rectifiers DOES need a heat sink, equivalent to 1.8 Volts * 35 amps = 63 if such current is flowing through the full bridge rectifier.

If 35 amps flows then the size of those square blocks are only good for 5 watts, they will get hot fast and fly apart.

DO NOT us the MX60 with the plans presented, they are not desinged for such "TRY OUT", I have been finding out that the MX60 does not like spikes above 120 volts PEAK, ( at least some of them).

Though the MX60 has 150 volts Fets the rest of the circuitry may not, so the limit is around 120 volts maximum.

DO NOT GUESS ELECTRONIC CIRCUITS "may work or not", unless you have a LOT OF KNOWLEDGE in Electronics.

EXPENSIVE GUESSING

Nando

Re: bridge rectifiers (3.00 / 0) (#12)
by halfcrazy on Sun Feb 11, 2007 at 06:29:50 PM MST

well it wasnt really a question of will it work it was more a question to see what is needed to do it safely. i realize rectifiers need heatsinks and if and when we do this we will monitor tempature of such heatsinks closely as we slowly let the mx's current limit up. i like boB's idea of the step down xformer then rectifiying along with the fast blow fuses. plus if the smoke comes out of the mx it will give us an excuse to buy another classic. i will continue to research and learn then we will regroup and see?

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#13)
by Countryboy on Sun Feb 11, 2007 at 08:51:34 PM MST

If you have a constant 120v AC that you want to charge batteries with, why don't you use a regular battery charger designed for 120v AC?

I don't see any advantage of using big rectifiers for battery charging unless you have varying voltages.

Dan did build an axial flux low rpm alternator for a small diesel engine a while back. A set-up like that might be usable for you, and you would need big bridge rectifiers then.

Re: bridge rectifiers (3.00 / 0) (#14)
by DanG on Sun Feb 11, 2007 at 11:03:58 PM MST

Couple of points - Trace says a true peak generator voltage equivalent to line AC is essential to proper function of chargers & many lower quality generators will not make the grade. In order for most inverters to make their ratings they need at least 164V peak AC input; At 150V peak AC my trace 120A charger will output only 60A at 14V where a 170V peak input will allow the full 120A of charging current to flow.

Outback realizes people will use various AC sources connecting to the MX60 through diode bridges but usually it is people doing just what you want to, getting back-up charging from their generators. As I recall Outback recommends an small value inline resistor to help limit surge current, they say their input filter caps will handle most noise. 120VAC will rectify to 60VDC, you may have loses dropping to a 24V or 12V system and getting batteries up will eat a lot of gas or diesel... but for monthly battery maintenance it is probably worth it

Re: bridge rectifiers (3.00 / 0) (#15)
by Flux on Mon Feb 12, 2007 at 01:44:16 AM MST

Diodes normally fail to short circuit, but in a bridge connection they are often blown open circuit by the fault current, so you may finally see it as an open circuit.

Diode failure is usually accompanied by trouble in other parts of the circuit.

What will a 35A bridge stand, that's another issue.There are virtually no circumstances where they will carry the full 35A indefinitely. The heat sink would need to be enormous and even then the temperature rise of the crimps on the tags will usually eventually result in failure.

Into capacitive loads ( or batteries ) I would consider the long term safe load to be 20A. If you use them as part of 3 phase bridges the rating may be less.

Single phase battery chargers running from small alternators cause trouble because the current is drawn at peak as a large spike and the alternator reactance is just too high and limits this peak current, those dreadful capacitor excited brushless machines with no AVR usually perform worst.

Using the MX60 would almost certainly work because the mx60 will change ratio to accept the drop in peak volts. I am not sure what is in the MX60 but you would ideally most likely need to use a choke after the rectifier to get the best possible results, but not knowing, I wouldn't advise you to experiment.

Stick to boB's advice and keep the input voltage well down and it should be ok, but that involves a transformer. I wouldn't even consider 120v rectified straight into it.

When you have gone to the trouble of another transformer you might as well build a battery charger that works with an inductor after the rectifier to maintain diode conduction for nearly 180 deg so that the alternator reactance doesn't have much effect. If you want charge control in it as well as a decent bulk charger then it gets complicated so if you have a redundant MX60 the idea may have some merit.

If you want reliable rectifiers to feed the MX60 then I would go for stud mount diodes, 3 anode positive and 3 cathode positive on 2 decent heat sinks and leave diode failure out of the equation.

Flux

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#25)
by DanG on Tue Feb 13, 2007 at 08:50:11 AM MST

http://www.xantrex.com/web/id/735/docserve.asp

Generator sizing and power factor correction document

Note the 5kw generator is listed as acceptable for 16.5 amp output.

That is 40% of generator face plate rating - you might try reducing the charger amperage demand to get a cleaner waveform and increase the chargers efficiency, plus add some resistance to generator output to provide some power factor correction...

[ Parent ]

Re: bridge rectifiers (3.00 / 0) (#19)
by asheets on Mon Feb 12, 2007 at 10:36:40 AM MST

Back to the original question... depending on design and the exact mode of failure, a full-wave bridge will either fail outright or turn into a half-wave bridge.
_____________________________

Alan Sheets

bridge rectifiers | 25 comments (25 topical)

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