Current Limiting to 80 Amp

use IGBT in rectifier section with sufficient rating

How big is the transformer in KVA rating and what was it originally used for?

Which is getting hot first or the windings or the core?

Also how hot is hot?

The transformer was made specifically for that purpose, it was made for that, as far as what is getting hot first, I really don't know, I know I smell something strong when it is on, but last time I tried it it stopped while charging. After 1/2 hr it stopped. I am not sure if the bridge went bad or the transformer, i want to get it rewind but now I need to make sure a limmiting current circuit is made for it.

thx

But was it and the rectifiers and related circuitry designed to charge big batteries at 80 amps for extended periods though?

A peak capacity rating is not anywhere close to a continuous duty rating in battery chargers. For example a 250 amp boost rated battery charger will only supply that 250 amp output for a few seconds and its continuous duty rating can be 1/10 that which puts any load greater that 25 amps on a limited duty cycle that rapidly tapers off from 100% down to fractions of a percent at 10X the output.

Basically that means that if your charger was not designed to run at 80 amps for extended run times its more than likely you already fried it.

How big of battery bank are you charging and what was your charger system originally rated for output current wise?

Well, it should have been rated for continuous current of 80 Amps, at least these were my parameter requirement when I sourced it out to be made. But I think my batteries are pulling far more that 80 Amps. This is why I think a limiting current of 80 Amps would work. The transformer design is sound, but I am draining more power than its spec. The battery bank seems to be able to pull as many Amps as it can get. I know this is Quantitative, but it is what I observed. So I think limiting current to around 80 amps will be what is needed.

thx again

It would be ideal if you have to rewind the transformer to use a center tap configuration and an SCR [ not as much power loss as an IGBT ] control on the output which can be set to a current limit of 80 amps. If your battery volts are low they will pull as many amps as they can get.

However a center tap [as against a bridge setup [ on your existing transformer wont allow you to deliver 80 amp continuous [ probably 40amp or so ] if that is what it was designed for. Why so many amps?

The amps are going to decrease as your battery voltage builds up so your transformer must have a peak voltage output more than this to enable some regulation.

Here's an off-the-shelf solution.

http://www.solar-electric.com/oufl80sochco.html

You can shop around and see if you can find a current limiter that suits you better. The recent popularity of photovoltaic systems has created a growing market for devices such as this one.

If you have cooked your transformer, better set a lower current limit.

That would be about 4KVA. That is a BIG transformer and may weigh over 100lbs (45kg). Does that appear to be correct?

A triac "dimming" circuit on the primary may work for you.

yes, i can hardly lift it... !

Before you assume that the heating is caused by wattage demands, be certain that the heat generated isn't caused by hysteresis. Loose core plates will do that.

One way to tell if hysteresis is at play is simply listen. If the core plates are loose, the 60 cycle vibration can usually be heard as the plates vibrate against each other.

In the past, a "cure" was affected by simply submersing the entire transformer in shellac. It's not as effective as rebuilding the core but it's one Hell of a lot less expensive!

Laughing Jaguar

It appears that you're charging your battery with a voltage source (the transformer+bridge output), whereas you should be charging it with a current source. You could add a linear current regulator, but at the 36V 80A (3kW) power levels you're talking about, these would dissipate too much power. Instead you need a buck-type switching current regulator. This involves a switching controller, some MOSFETs and a large inductor. Moreover, to avoid ruining your batteries, you'll need a charging controller, to recognize when to switch from current into float mode, etc. What's more, when you say 36 volts, that's really 36 to 42 volts, depending on the charge state of the batteries. You could design and build all this yourself, but it'd be cheaper, safer and quicker to purchase a commercial charger.

But if you wish for a design project, you could use an LT3845 switching controller (link), typical block diagram above, to run the MOSFETs and step-down inductor, plus an LTC4000 charging controller to run the LT3845. These chips work with up to 60V inputs, so they'd be fine for a 36V battery, and you can use large MOSFETs to handle 80A. Linear Technology gives good information about how to design with these chips, but you might find their 66 pages of dense information a bit tough to swallow.

If your 36V battery is really three 12V batteries in series, they should be individually monitored and controlled, so you don't overcharge one of them. There are ICs designed for this task as well.

I would recommend a rectifier that is capable of being loaded to 200% of known load. The primary purpose is to not overload the charger, always keep in mind, if you are going to load any electrical device, never push it past 80% of full load ratings. Otherwise your tool will be at risk of failure sooner than you want.

Being it will have a 220/240Vac input, transformed down to 125% of you DC voltage load, use of SCR/IGBT bridge, output set to 110% of working voltage average operating of your batteries. Being if you are charging 12Vdc, 24Vdc, 48Vdc batteries, you will have a definite switch to select your output standard voltage, and then the system is overall set to work in a current mode configuration.

This will stay steady at your selected voltage and only the current demand factor will change in charging your batteries. It is the same principle used as in platting materials.

The resistance of the load is the governing factor on how much current is actually being called for, on demand to complete the process. Most the rectifiers I work with are 12Vdc output max, but capable of reaching loads up over 6000amps. These rectifiers are designed to run 24/7 and all have internal cooling systems with heat exchangers routed to external cooling towers.

I would recomend to us Dynapower, located up in Berlington Vt., they are the leading company in the USA for rectifiers. Our battery shop uses charging equipement on the same principle as the plating rectifier. The biggest requirement is the cooling system. If you do not have an adiquate cooling system built into your unit, it will not be capable of running for extended periods of time. And the maintenance is very minimal on the upkeep of these units. Good luck, Maximo

You can use an inductance in series with the primary or secondary to increase its impedance with minimal losses. This will make it closer to a welding machine transformer that has so much leakage inductance that you can short circuit it.

In general, transformer's leakage inductance have an impedance of 5-10%. You may want to increase this to 25-50% depending on the battery voltage with respect to the DC open circuit voltage coming out of the rectifier.

To calculate the % of impedance, read this paper.

http://www.baldormotion.com/support/SupportMe/Downloads/DocsLib/H2%20Application%20Note%20Percent%20Impedance.pdf

Now I am obligated to tell you the whole setup, I was avoiding it just to help focus on the problem, I thought that was better. But here you go.

Now I am using the MPPT Flex 60 from Outback to charge the batteries, but in winter I do not have enough power to equalize the battery bank, and I sometimes leave the dweling for many months, and equalizing charge becomes more important to get the most out of the battery bank.

So I purchased the transformer, being discussed, to do just that, I assume I will use it only few times a year, for 6 hr or so at a time....

In that case, just use a power resistor in series. Assuming that you place the resistor in a safe place in your house, the power losses by the resistor will simply reduce you heating bill.

If it is only for a short time every few months, don't even worry about the power losses during equalizing.

The resistor could be as simple as a few meters of stainless steel wire wrapped around a concrete block. Just don't touch it when powered... (and keep kids, dogs, and cats away)

So do you at least have a amp meter and volt meter on his thing so you can see if its actually working in the intended voltage and current ranges its supposed to?

If you had it wound for 36 VAC output to charge a 36 volt DC battery bank you already have a problem as stated earlier.

How many Amp Hours is your battery bank rated for?

Thanks for all the replies. My battery bank is 400 AH. The idea of resistor in series is a nice solution. I will place it in safe location for sure. No cats or dogs around!...

thx

how long is the charger running before it overheats while recharging the battery bank?

A properly designed 80 amp capacity charging unit should not have any trouble with a 400 AH battery bank.

I occasionally charge the 200+ Ah 12 volt deep cycle battery set on one of our tractors with a common 20 amp battery charger without burning anything up even when they are severely drained and the charger has to run flat out for over 15+ hours to get them fully recharged.

To me this still sounds like a improperly designed charging system.