Let's design our own UPS

[PaulGherkin]

When I have had a decent night's sleep tell you what I will do, I have a decent bench power supply, a digital one, I will demonstrate this experimentally

 

[wingnut771]

So that you are aware that the battery will suck 25A or thereabouts (as these behind me do) when the charger is on.

As for what happens when you have a charger capable of 100A, about 25A is drawn for about an hour and a half, then it goes down.

As for what happens when your charger is too small (like one of mine was), when the power comes back on, the charger says goodbye, nice knowing you.

The home-made inverter, the charger I used there, can do 80A, it battles and moans a bit because the batteries are sucking 30A to charge and the inverter is sucking the rest but it can do 80A, the batteries draw never more than 30-40A when charging.

I also confirmed this on the Synapse inverter I bought, as it displays the current while charging, and that follows the curve I drew, precisely.

I was taught these things in high school by a BSc engineer who worked for Plessey.
He showed me how alarm systems charge their batteries.... its a simple 13.8 - 14.2V regulated power supply and since the alarm battery draws less current than a deep cycle battery when its time to charge, it just works. Texecom, Paradox, FBII and many others used this for decades.

I have a 100Ah deep cycle AGM battery and one of these which is only 5A, why doesn't this blow up, it just takes frikken long?:

 

[DuracellBunny]

The battery does it.... the battey just pulls less and less current and then settles around 800mA after a good 22 hours.

This is used extensively in gate motors, surprised people don't know this. And your car's alternator can't adjust how much current it delivers, if it did, your headlight brightness would go all whacko

Not sure if im understanding correctly, from as much as I know the Alternators voltage regulator controls the output to match the battery, to ensure that the battery isnt over charged, failed voltage regulators have been known to kill batteries. ie Boil, Swell and kill cells. A car battery and alternator are on the same circuit to power electronics in the car, possibly why you can still switch things on without the alternator running, and the alternator regulator needs a sense wire from the battery to give it a signal to produce power, Otherwise it would just spin for no reason and not produce any volts or amps. I could be wrong,

 

[BoxFish]

As far as I understand a battery will draw whatever current it can until the internal voltage matches the charger voltage depending on the internal resistance of the battery. A charger is supposed to limit the current itself to prevent self damage and damage to the battery. That is why the current curve is flat in the beginning as it is the charger doing the limiting not the battery. Only once the battery is near charged does the battery draw less current at a fixed voltage slowly tapering off until the battery is full. An automotive battery is designed for high current bursts used for starting car engines. It supposedly can tolerate brief high charge current due to its design. A deep cycle is designed for long time discharges and does not tolerate high charge currents. That's what I understand the 0.25C charge rate limit for deep cycle, gel, agm etc to be.

 

[PaulGherkin]

I have a 100Ah deep cycle AGM battery and one of these which is only 5A, why doesn't this blow up, it just takes frikken long?:
View attachment 1177550

It doesn't blow up because it has what is called fold-back. Remember I am using Chinese switched mode power supplies. My wife has lost her job and I am on a limited budget. I have one of those and it takes long because it runs special algorithms to optimize the battery

 

[PaulGherkin]

Not sure if im understanding correctly, from as much as I know the Alternators voltage regulator controls the output to match the battery, to ensure that the battery isnt over charged, failed voltage regulators have been known to kill batteries. ie Boil, Swell and kill cells. A car battery and alternator are on the same circuit to power electronics in the car, possibly why you can still switch things on without the alternator running, and the alternator regulator needs a sense wire from the battery to give it a signal to produce power, Otherwise it would just spin for no reason and not produce any volts or amps. I could be wrong,

Like I said earlier, a car alternator with no load can easily deliver over 100 volts DC with the regulator blown.
The one case I sorted out in high school, the Bosch regulator died, the client elected to drive the car to me, it stank like a rotten egg, because 20 volts + was being sent into the poor battery. Fortunately no ECU, all carburetor, he did complain about burnt out dash lights etc...

 

[PaulGherkin]

As far as I understand a battery will draw whatever current it can until the internal voltage matches the charger voltage depending on the internal resistance of the battery. A charger is supposed to limit the current itself to prevent self damage and damage to the battery. That is why the current curve is flat in the beginning as it is the charger doing the limiting not the battery. Only once the battery is near charged does the battery draw less current at a fixed voltage slowly tapering off until the battery is full. An automotive battery is designed for high current bursts used for starting car engines. It supposedly can tolerate brief high charge current due to its design. A deep cycle is designed for long time discharges and does not tolerate high charge currents. That's what I understand the 0.25C charge rate limit for deep cycle, gel, agm etc to be.

Thanks that's what I have been trying to say. I don't do words, I have a disability so there.

 

[BoxFish]

Thanks that's what I have been trying to say. I don't do words, I have a disability so there.

Hence my original question. The charger is supposed to limit the current not the battery. If you use a deep cycle then the charger should be set to limit the current to 0.25C. If you use a 100ah deep cycle then the charger must be set to a max of 25A. I don't know what batteries you have but is your 80A limit too much?

 

[Flanders]

I'm clueless with this stuff - pls hulp!

I have a Invisimo-2000 ups:

Input: 230Vac, 50Hz, 15A Max
Output: 230Vac, 50Hz, 2000VA/1200W
DC Input: 24VDC
Charger Current: 40A Max

It's sitting with 2 x Cooper enertec 105AH 12V sealed lead acid batteries which are screwed after two years and these have already been replaced once and were not cheap.

Can I go with a lithium-ion solution like the Hubble S-100? Which model and how many would be best etc?

The trolley/battery box compartment is ~ 36cm x 39cm x 27cm high. Obviously I will make a plan and make my own box if need be.

Initially this setup was able to run 2x pcs, router, ONT and a TV with dstv decoder and would last for the normal 2.5hr duration. Very soon after the latest battery replacement I noticed that it would kick out with that load and I'm not really sure why. The one pc did have a GPU upgrade however is not used for gaming or anything crazy during loadshedding.

Any pointers would be much appreciated.

 

[Ivork]

I'm clueless with this stuff - pls hulp!

I have a Invisimo-2000 ups:

Input: 230Vac, 50Hz, 15A Max
Output: 230Vac, 50Hz, 2000VA/1200W
DC Input: 24VDC
Charger Current: 40A Max

It's sitting with 2 x Cooper enertec 105AH 12V sealed lead acid batteries which are screwed after two years and these have already been replaced once and were not cheap.

Can I go with a lithium-ion solution like the Hubble S-100? Which model and how many would be best etc?

The trolley/battery box compartment is ~ 36cm x 39cm x 27cm high. Obviously I will make a plan and make my own box if need be.

Initially this setup was able to run 2x pcs, router, ONT and a TV with dstv decoder and would last for the normal 2.5hr duration. Very soon after the latest battery replacement I noticed that it would kick out with that load and I'm not really sure why. The one pc did have a GPU upgrade however is not used for gaming or anything crazy during loadshedding.

Any pointers would be much appreciated.

I would say yes. You would need two of them since it's a 24v inverter.

I use one on my Ellies inverter and the Mecer guys use them as well.

Mecer 2400VA Inverter (Community Support)

What did the lead acid show at those points? Somewhere in this thread. Can not remember, sorry. I THINK it was around 26V / 25.9V

mybroadband.co.za

 

[Düber]

Not sure if im understanding correctly, from as much as I know the Alternators voltage regulator controls the output to match the battery, to ensure that the battery isnt over charged, failed voltage regulators have been known to kill batteries. ie Boil, Swell and kill cells. A car battery and alternator are on the same circuit to power electronics in the car, possibly why you can still switch things on without the alternator running, and the alternator regulator needs a sense wire from the battery to give it a signal to produce power, Otherwise it would just spin for no reason and not produce any volts or amps. I could be wrong,

There are various designs of automotive alternators but to simplify thing lets consider one wire and three wire ones.

A one wire alternator is self exciting and only needs a connection to a battery and a mechanical force turning it for it to start charging, a relatively simple and blunt instrument. These usually need a good rev or two before they start charging.

A three wire alternator needs a charging connection to the battery, a sensing/feedback circuit( sometimes common with the charge cable) and an excitation connection. The excitation circuit comes off the ignition and energizes the coils to "kickstart" the alternator, these alternators won't start charging without it.

The regulators job is to take the DC coming from the rectifier and keep it clamped at a voltage that is safe for the battery (or batteries) depending on the amperage that is being drawn and the RPM.

As @PaulMurkin explained the battery will take the amp's it needs, as will the other electrical items, headlights, ECU, ignition coil etc. so alternators have a relatively high amperage rating to cater for everything.
If the regulator packs up it lets the voltage climb and because of this the battery starts overcharging and boiling.

 

[Gnome]

I have a 100Ah deep cycle AGM battery and one of these which is only 5A, why doesn't this blow up, it just takes frikken long?:
View attachment 1177550

There is so much misinformation in this thread.
Its like a mine field.

But perfectly agree with you, this charge will not blow up no matter how big your load is. (no pun)
Assuming it isn't designed terrible.
Lead acid and lithium batteries rely on constant voltage, constant current chargers.

If the voltage reaches the set threshold it clamps at a constant current.
If the current exceeds the amount the charger can provide the voltage is at whatever voltage the charger can provide its maximum current.

A one wire alternator is self exciting and only needs a connection to a battery and a mechanical force turning it for it to start charging, a relatively simple and blunt instrument. These usually need a good rev or two before they start charging.

Just about every car alternator I've seen sits at 14v at idle.
They regulate the voltage to a maximum of ~14v
So it is definitely charging at that point

 

[chrisc]

I have successfully used step-up buck converters to change 12V to 48V and 55V to keep PoE switches operational during load-shedding. They are 96% efficient

They cost about R200 each

 

[Düber]

Just about every car alternator I've seen sits at 14v at idle.
They regulate the voltage to a maximum of ~14v
So it is definitely charging at that point

That's the benefit of having the excitation circuit on the " three wire" alternator, the alternator starts charging straight away.

One wire alternators are only really found on older vehicles, mostly American stuff if memory serves and I have had them on some tractors. They literally only have a one thick wire on them going to the battery, no extra plug. Once excited it will obviously charge at idle, some are better at self exciting than others.

 

[x7razor]

I have successfully used step-up buck converters to change 12V to 48V and 55V to keep PoE switches operational during load-shedding. They are 96% efficient

They cost about R200 each

Which ones did you buy since the price is so high?

 

[DuracellBunny]

There are various designs of automotive alternators but to simplify thing lets consider one wire and three wire ones.

A one wire alternator is self exciting and only needs a connection to a battery and a mechanical force turning it for it to start charging, a relatively simple and blunt instrument. These usually need a good rev or two before they start charging.

A three wire alternator needs a charging connection to the battery, a sensing/feedback circuit( sometimes common with the charge cable) and an excitation connection. The excitation circuit comes off the ignition and energizes the coils to "kickstart" the alternator, these alternators won't start charging without it.

The regulators job is to take the DC coming from the rectifier and keep it clamped at a voltage that is safe for the battery (or batteries) depending on the amperage that is being drawn and the RPM.

As @PaulMurkin explained the battery will take the amp's it needs, as will the other electrical items, headlights, ECU, ignition coil etc. so alternators have a relatively high amperage rating to cater for everything.
If the regulator packs up it lets the voltage climb and because of this the battery starts overcharging and boiling.

I think the main question I was heading at is what protection would the battery have to prevent it from being cooked. Yes a one wire alternator is self exciting meaning that the sensing circuit is built into the alternator, when the alternator spins, this circuitry connects the internal voltage regular to the battery and turns the alternator on.

All electrical items as far as I know are all connected on the same circuit as the battery and alternator, so as the alternator produces power it supplies it to all the needed electronics and bring the battery back to its full state.

If I had to take a battery and just keep feeding it 20amp charge would this not cook the battery? As I understand a Float charge is there to keep the battery in its full state without cooking the battery by reducing the amps.
So how would this battery that i feed 20amps without any reduction of power after the battery is full, would this not cook the battery or shorten its life drastically? How would the battery tell the charger enough?

Thats basically what im trying to get at, How would a battery cut off in order to protect itself if it is consistently being fed 20amps.

 

[wingnut771]

I think the main question I was heading at is what protection would the battery have to prevent it from being cooked. Yes a one wire alternator is self exciting meaning that the sensing circuit is built into the alternator, when the alternator spins, this circuitry connects the internal voltage regular to the battery and turns the alternator on.

All electrical items as far as I know are all connected on the same circuit as the battery and alternator, so as the alternator produces power it supplies it to all the needed electronics and bring the battery back to its full state.

If I had to take a battery and just keep feeding it 20amp charge would this not cook the battery? As I understand a Float charge is there to keep the battery in its full state without cooking the battery by reducing the amps.
So how would this battery that i feed 20amps without any reduction of power after the battery is full, would this not cook the battery or shorten its life drastically? How would the battery tell the charger enough?

Thats basically what im trying to get at, How would a battery cut off in order to protect itself if it is consistently being fed 20amps.

The way I understand it is rather look at it the battery pulling amps instead of the alternator feeding amps. Alternator has the capacity for 20 amps, doesn't mean that's what gets used.

 

[DuracellBunny]

The way I understand it is rather look at it the battery pulling amps instead of the alternator feeding amps. Alternator has the capacity for 20 amps, doesn't mean that's what gets used.

Wouldn't a lead acid battery accept anything that is being fed to it? A charge source will keep feeding the battery and the battery will happily accept this regardless if its full. So how would the battery effectively stop itself from being over charged to avoid damage to it, if the charger doesn't do this automatically to protect the battery?

 

[PaulGherkin]

Wouldn't a lead acid battery accept anything that is being fed to it? A charge source will keep feeding the battery and the battery will happily accept this regardless if its full. So how would the battery effectively stop itself from being over charged to avoid damage to it, if the charger doesn't do this automatically to protect the battery?

As mentioned before.. the battery draws current during charging...
As the chemical reaction takes place this current drawn dwindles down to a few hundred milli-amps after some time. The curve I drew is the current drawn versus time

The scenario is completely different for other types of batteries.

I have designed about four chargers during my lifetime for lead acid batteries that went into full mass production. No battery was ever boiled or over-charged that I know of.

I am now going to give you a small-scale example.
Equipment:
Multi-meter (Fluke 77 or similar)
Charger: Output 13.8VDC regulated from a 22VA transformer
Battery: 12V 7.2Ah "gel cel" used for alarms. Condition = FLAT

What happens:
Charger is connected to battery while its output voltage is measured. Immediately the voltage will drop down to some value around 10 volts DC because the battery is sucking as much as the charger can give, typically 1.1A, the regulator in the charger (typically LM317T adjustable positive voltage regulator) is getting nice and hot. 1.1A or slightly more is flowing at this point.

The above carries on for around 60-90 minutes, then the voltage begins to rise across the charger, and the current being drawn from the battery starts to decrease. This continues for another 8 hours or so until the voltage has reached 13.8V matching the set point of the regulator, and the battery is probably drawing 100mA around this time... now its in float charge mode, and the current drawn, will slowly decrease over time down to about 50-60mA after 24 hours.

The charger has done nothing but give... it has not done anything else. I have used this principle on deep cycle lead acid batteries here, using massive switched mode power supplies to charge the batteries. It works.

 

[BoxFish]

@PaulMurkin What brand/type battery are you using and the capacity?