DIY Regen Battery tweak

[randytsuch]

Thanks John for make so simple that even I understand and feel the challenge to do it! :)

Pearse, just curious what are you using between the Regen and Lampi? USB adapter, or cable?
And how long are your DC cables from 3.3 battery to the Regen?
Any pictures of the set-up?

So John didn't mention this, and this may be obvious, but there are a couple other things you need.

A switch between the Regen and the battery. Otherwise, your battery won't last long. Unless you connect a 3.3V power source to the battery, and leave everything on all the time.

The other thing you need is a 3.3V power source, to keep the battery charged. I've made some 3.3V power sources lately for my batteries using a 5V walwart, and then I build a linear regulator with a LM317, a resistor and a pot. It's pretty simple to make them.

Randy

[jkeny]

Thanks Randy
It's great to see others pitching in & adding their thoughts/suggestions - yes a switch is recommended
I do recommend leaving the 3.3V regulated PS (not a LiFePO4 battery charger) trickle charging & connected at all times to avoid the battery running to below recommended minimum voltage of 2.7V which, can damage the battery.

As well as this, recharging from a low charger has special considerations - the battery will attempt to draw a lot of current from the PS so the PS has to be able to handle this, by being current limited. The best solution is to always trickle charge the battery.

John Swenson has commented on this battery scheme over on ComputerAudiophile

"DO NOT under ANY circumstances use the internal 3.3V regulator to charge a lithium battery!!!!

These batteries have a very low impedance, hooking one up to the regulator in the REGEN will try and pull 50A or so out of it, which will current limit down to 1.2A or so. When it does this the voltage will be very low (there is a very low resistance path between the regulator and where the recommendation is to put the battery), which means almost the entire raw supply voltage will be converted to heat by the regulator. For a 7.5V input that is over 8 Watts. This will heat up the reg chip VERY fast, it will hit its thermal limit and drop the voltage even further. The reg chip is designed to live with this temperature for a short time, but it will fry if left in this state for long.

Even worse the whole board will quickly get into this temperature range and many of the other parts on the board are not designed to withstand this temperature, thy will fry within a few minutes of this condition.

So using the internal regulator as a charger for a lithium cell is almost guaranteed to well and truly fry the REGEN.

BTW the above scenario is NOT covered by the warrantee."

"On using a 3.6V charger with the HUB and clock chips.

This will probably work, BUT it places very high stress on the transistors inside the chips, which will radically shorten their lifetime.

So instead of a lifetime measured in decades, you get a lifetime measured in months. It is that long because the chips are done in an older technology which can withstand this for a longer period. With the newer chips it would be weeks.

So yes it will probably work, but not for long."

I agree with what he says but again reiterate:
- trickle charge the LiFePO4 battery with a regulated 3.3V PS permanently connected, NOT a LiFePO4 battery charger (thus avoiding > 3.3V)
- I didn't propose using the Regen's onboard 3.3V regulators as the trickle charger but when people asked about using it, I suggested trying it. Once this regulator is ONLY ever trickle charging, there should be no strain on that regulator chip.
- Don't allow the batteries to go low in charge. This could happen if you don't have the trickle charger connected/powered & you are running the Regen off the battery. If you are going to store it away for a period of time then disconnect the battery from the unpowered charger.

If these recommendations are followed this should operate without a hitch.

[Sligolad]

Thanks John for make so simple that even I understand and feel the challenge to do it! :)

Pearse, just curious what are you using between the Regen and Lampi? USB adapter, or cable?
And how long are your DC cables from 3.3 battery to the Regen?
Any pictures of the set-up?

I have a Short Supra USB Cable between PC and Regen and the same again between Regen and DAC Adam.
Currently I am using a Paul Hynes SR7 12v supply for the Regen as I have not got around to the Regen battery mod yet, I have thew battery and charger already to go but too many projects lately.

I have heard John's Battery Supply Regen on 2 occasions and on both it easily beat my Paul Hynes supplied Regen.
Cheers, Pearse.

[randytsuch]

John
As you pointed out, a constant 3.3VDC regulated power works great for keeping lifepo4 batteries charged, it is what I'm doing in my PC, and in my DAC.

To "current limit" the charging current, in my dac project, I added a one watt, 1.5 ohm resistor between the charger and the 3.3V power supply. I didn't measure the current, but it seems to work ok there. The value of the resistor will depend on the current draw on the battery, but it will need to be a low value to keep the battery charged. I have a pack of one watt resistors to choose from, made it much easier to find a value that worked. With a higher resistance, the battery voltage would slowly drop if my dac was turned on. I really did this because I have two batteries connected to the same charger, and I wanted to add some resistance between the batteries, so they won't charge each other, at least not with too much current.

Another trick I sometimes use is to use a double pole switch to control both power to the load, and charging power. On one side of the switch, one pole connects to the battery, and one pole connects to 3.3V regulated power. On the other side, both poles are shorted together, and tie to the load. So, when you turn on the switch, both battery voltage, and 3.3VDC from your battery charger are connected to the load, and each other. This keeps the battery charged up whenever you are using power from the battery.

Note that if you have the battery charger always connected to the battery, and you turn off the charger, it may drain the battery.


Randy

[sima66]

Thanks guys for the input.

I will use this blueprint for charging:
viewtopic.php?f=15&t=3618&start=10
The REG. is the 3.3v line from my TeraDak PS.

The idea was to use the USB adapter to connect Regen to Sonicweld, but than I will need at list 3 feet DC cable from battery to Regen.
Regen should be closer to the DAC side, right??
Any thoughts on that, or different aproach?

[rickmcinnis]

It is recommended to use the adapter so REGEN and the DAC are in intimate contact.

One should wonder if REGEN should not share any power connection with any other component for improved isolation.

And the conclusion should be: it should not.

[sima66]

It is recommended to use the adapter so REGEN and the DAC are in intimate contact.

One should wonder if REGEN should not share any power connection with any other component for improved isolation.

And the conclusion should be: it should not.

My Sonicweld needs the 5v from USB! :(

[rickmcinnis]

You could cobble up some 5 v supply to get the ball rolling and then disconnect it after the components agree to work with each other?

Unless this 5 volts is required at ALL times and then that would be sad!

Just might require a little better supply to not infect the rest of your circuit.

[jkeny]

Or DIY something like this - it's simply a USB adapter with the 5V internally disconnected & brought out on a flying lead so that a clean 5V supply can be injected - it's from the Aqvox site

[nige2000]

heres my 2nd attempt at it
nice improvement in clarity