(Topic ID: 77275)

Memory Capacitor Fans - WPC support question


By Schwaggs

5 years ago



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  • 32 posts
  • 12 Pinsiders participating
  • Latest reply 4 years ago by barakandl
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    #1 5 years ago

    I have used memory capacitors on all my games (Williams system 6 and 11) to date as opposed to relocating the battery holder and it works great. My latest acquisition is a WPC-S era machine.

    Do memory capacitors work on WPC era machines? In other words, does the backup memory draw low enough current to make this viable?

    Is the correct diode to bridge to power the capacitor D2? I only have WPC schematics, not WPC-S schematics. Is it D2 on both WPC and WPC-S?

    Any advice is appreciated, I prefer NOT to cause problems on this board!

    #2 5 years ago

    I don't see any reason why it wouldn't work, the principle is the same. And I believe D2 is the right location for it, but double-check with the meter beforehand. Worst case scenario is that it is the wrong place to draw +5v from and the CPU doesn't boot. Shouldn't cause any lasting issues though.

    #3 5 years ago

    I'm going to give it a try. I will look closely at the board traces to make sure D2 is correct. I will let you know how it goes...

    #4 5 years ago

    I'd like to know how long it can go with the power off in a WPC machine - please let us know!

    #5 5 years ago

    The difference about using a memory cap in a WPC machine is that in addition to preserving the memory it also has to support the real time clock, so the power draw is greater. I've heard of people getting 2+ weeks with a memory cap and WPC which is probably ok for a collector who plays their game sporadically.

    Unless your game has a midnight madness mode or you are so fastidious that your machine has to have the correct date and time, you're better off putting in a NVRAM solution IMHO.

    viperrwk

    #6 5 years ago

    For $3.91 per cap on mouser, you can't really go wrong. Viper, have you by any chance experimented with higher value super capacitors than 1.5F? I see 5F caps there for around $10, I'd imagine they'd last more than twice as long, with the discharge rate being the same?

    #7 5 years ago
    Quoted from thedefog:

    For $3.91 per cap on mouser, you can't really go wrong. Viper, have you by any chance experimented with higher value super capacitors than 1.5F? I see 5F caps there for around $10, I'd imagine they'd last more than twice as long, with the discharge rate being the same?

    No I haven't. There are apparently issues with initial current inrush on an empty supercapacitor and the circuit on the CPU board may not support this. Unless someone like Ed @ GPE or someone else who has experience with supercapacitors can chime in here to the contrary, I personally wouldn't try it.

    viperrwk

    #9 5 years ago

    Makes sense. Thanks for posting!

    viperrwk

    #10 5 years ago

    Some great information, thanks!

    I have been using the GPE 1.5F memory caps in my machines but was getting only 7-10 days of backup on my System 11 machine so I ordered a 4F cap and it has been working fine so far. I use straight jumpers over the blocking diode and haven't had any problems with that setup.

    The traces on the WPC board are much smaller than the System 6 and 11 boards so I will try using a 56 ohm resistor and report what I get. I will not be able to report how long the 4F cap lasts since I am playing the heck out of the game at the moment. I will post back when installed within the next few days or so...

    #11 5 years ago
    Quoted from Schwaggs:

    Some great information, thanks!
    I have been using the GPE 1.5F memory caps in my machines but was getting only 7-10 days of backup on my System 11 machine so I ordered a 4F cap and it has been working fine so far. I use straight jumpers over the blocking diode and haven't had any problems with that setup.
    The traces on the WPC board are much smaller than the System 6 and 11 boards so I will try using a 56 ohm resistor and report what I get. I will not be able to report how long the 4F cap lasts since I am playing the heck out of the game at the moment. I will post back when installed within the next few days or so...

    Just for reference, the resistor on a Bally board is 270 ohms between the battery and the RAM. Nobody changes that resistor, so 270 ohms would be a fine value to use.

    #12 5 years ago

    Used a 270 ohm resistor to bridge D2 and connected the 4F cap to the battery holder to make reversing the mod easy and invisible. Voltage to the CPU board is 5.02V, at the resistor is 4.8V (drop due to D1) and at the cap 4.67 after about 45 minutes of charging. With the power off, voltage drop across the resistor is .01V which is the resolution of my portable meter so it could be .14 or .04V drop, or less. Assuming it truely is .01 volts, that would be a power draw of 40 microamps. Assuming the memory and clock needs 4V to work, the capacitor can provide about 7 days of backup at 40 uA draw. if the draw is less (could be if my meter is off), it could be around 2 weeks. Time will tell...

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    #13 5 years ago

    I don't think the 270 ohm resistor is going to work. It doesn't allow the capacitor to charge quickly enough.

    I let the machine run for several hours yesterday after installation and turned the machine off. The voltage on the cap was in the 4.7V area at shutdown. Supply voltage is 4.8 so admittedly, it was not fully charged. This morning at 8AM it was already down to 3.94V and at 6PM it was at 3.61V. Memory was still preserved at this voltage, which is encouraging. However this much drop in roughly 20 hours is not going to cut it.

    I measured the voltage drop with the the machine off and since the voltage is below 3V my meter has .001 resolution and it is .006V. I calculated the current draw at 20 uA which according to the formula I found online should yield a 14 day run time on a fully charged 4F cap. Actually a little more if you consider the memory loss low voltage threshold is below 4V.

    I calculated the current flow (.53V drop across the resistor) with the machine on (charging current) and it is only 1.6mA through the resistor. To fully charge this cap with this configuration will take days at 1.6mA.

    So my next test is to jumper the 270 ohm resistor with some test lead and let it charge (happening now). I will measure the voltage of the cap after power down and again tomorrow evening and report findings then...

    #14 5 years ago

    WELLLLLLL the results are in and its not good. I charged the capacitor with the resistor jumped by test leads for several hours then turned it off and measured the caps voltage over the following days. This is what I found:

    4.84V - Charging Voltage
    4.82V - 11:00PM - Cap voltage a few seconds after turning the machine off - this represents almost a full charge since it is so close to the supply voltage
    3.84V - 8PM following day (~1 day)
    3.25V - 8PM next day (~2 days)
    2.85V - 8PM next day (~3 days)

    It turned the machine on after the voltage hit 2.85 fully expecting the memory and clock to be wiped but is was still preserved. I'm fairly sure memory wouldn't be preserved much longer so I'm calling the useable backup duration of a 4F capacitor on a WPC-S era machine to be around 3 days. Not very workable for many people but would work if you play a lot or if the machine is on route.

    #15 5 years ago

    i've been experimenting with a Demo man and a cr2032 coin style battery. installed it about 6 months ago and it's still holding. that's like half way between doing a remote AA battery mod and a memory cap i guess.

    #16 5 years ago
    Quoted from cfh:

    i've been experimenting with a Demo man and a cr2032 coin style battery. installed it about 6 months ago and it's still holding. that's like half way between doing a remote AA battery mod and a memory cap i guess.

    After seeing you do this a few times on Ninja videos i am now using all coin style batteries on all my boards. I really like that setup, cheap, easy, effective. My -35 and s6 test boards have been going on at least a year now with cr2032. I have probably sent out 100 MPUs with them installed and no reports of early failure yet. I just do bally and wms SS though.

    I did put a cr2032 in a TSPP to test as well. That is only going on 2 months though. We'll see.

    #17 5 years ago

    i use cr2032 all the time in DE and whitestar boards. they work great there.
    the only thing that doesn't like them are system7 williams boards. they don't seem to last there.

    9 months later
    #18 4 years ago
    Quoted from cfh:

    i use cr2032 all the time in DE and whitestar boards. they work great there.
    the only thing that doesn't like them are system7 williams boards. they don't seem to last there.

    I know this is an old thread but was wondering if you need a blocking diode for the CR2032 and it's orientation for Sys 11 as I'd like to try this on a machine.

    #19 4 years ago

    There is a blocking diode already on the sys 11 board. You have to add a diode on a games that used a rechargeable batter, like early bally.

    I always check to make sure the diode isnt shorted when i install a cr2032.

    I am trying a cr2032 in a gtb 80b. I noticed the battery powers a few more ICs besides the RAM. 2 months or so and no problems yet. Voltage is steady.

    #20 4 years ago

    Update on the 4F cap in my WPC-S era machine. I never got around to removing the cap and going back to batteries. With the 4F cap, I get over a week of backup and have not lost the settings, even after 7-10 days. However, the clock DOES NOT keep time. It loses several hours each week so other remote battery solutions are warranted if you need the clock.

    #21 4 years ago

    just out of curiosity wouldnt it be easier to install one of those Ram chips that doesnt need power? I think Boryguard sells them.

    #22 4 years ago

    The ram is hard soldered in and the real time clock wouldn't run.

    Quoted from jamieflowers:just out of curiosity wouldnt it be easier to install one of those Ram chips that doesnt need power? I think Boryguard sells them.

    6 months later
    -1
    #23 4 years ago

    Folks:

    It's been 6 months. Has anyone pursued this subject further?

    #24 4 years ago

    Still have the 4F cap in my I500 and its working fine to save settings and scores. I have left the machine off for 2 weeks without loss of data.

    I used caps like these. $2.50 per machine isn't bad for a permanent backup solution. ebay.com link » 4pcs 4f 5 5v Coin V Fitn Farad Ultra Capacitor Super Capacitor Memory Backup

    #25 4 years ago

    At 4F -- a discharged cap would look like a dead short to your power supply at startup. What size resistor do you have installed to limit the current?

    #26 4 years ago

    Ed, I jumpered the diode with a 270 ohm resistor for that very reason. I think that may be a little big as it reduces the charge rate to about 1.6ma.

    #27 4 years ago

    I just installed a 5F supercap in a TZ. I replaced D2 with a 100 ohm resistor to limit current to 50mA.

    The charge rate is tau=RC=500 seconds. For 5 tau to be fully charged, thats 5*500=2500 seconds or 42 minutes.

    1 week later
    #28 4 years ago

    I've had the 5F supercap in TZ for just over a week and here are the results.

    With D2 replaced by a 100 ohm resistor, it takes about an hour to charge the capacitor as expected.

    After a week of the game being off, the capacitor voltage is around 2V. The memory settings are still holding, but the timekeeping is way off.

    There are 2 separate things going on here:

    1) The capacitor is self discharging due to inherent parasitic leakage. The manufacturer of the capacitor lists this as 25uA on the datasheet. A bit of RC calcs shows that with this leakage, the capacitor will discharge on it's own in about 23 days.

    2) Current is being consumed to a) Support the RAM and b) Run the real time clock/calendar. This measures out to a total of 20uA. Adding this to the 25uA for leakage gives 45uA. More RC calcs shows that with this total current, the capacitor will discharge on it's own in about 14 days.

    However, the 2 loads a) RAM and b) real time clock/calendar each have different minimum voltages to "stay alive". The real time clock/calendar seems to stop working at about 3 volts while the RAM seems to hold it's settings all the way down to near 1 volt.

    The result is that after about 3 days, the real time clock/calendar will start to lose time. After about 10 days, the RAM settings will be lost.

    The RAM current can be reduced by installing Non-Volatile RAM (NVRAM), but if you want accurate timekeeping, the capacitor leakage will still do you in after 2 weeks.

    One key point is that bigger capacitors offer no help. The leakage of most supercaps is essentially proportional to the capacitor rating. Larger capacitors or multiple capacitors in parallel yield no help.

    #29 4 years ago

    Jim - Thanks for the info. In this case, I'm sticking with batteries. Like in TZ, I like my games to have current date/time.

    #30 4 years ago
    Quoted from JimWilks:

    I just installed a 5F supercap in a TZ. I replaced D2 with a 100 ohm resistor to limit current to 50mA.
    The charge rate is tau=RC=500 seconds. For 5 tau to be fully charged, thats 5*500=2500 seconds or 42 minutes.

    5F is one heckofa capacitor!
    Limiting the charge current is definitely required there but still gotta watch for heat. That's 0.25 watts being dissipated by the current limiting resistor. Make sure to use a resistor -at least- 2x the anticipated power being dissipated. I normally don't like to drive a resistor at anything more than 25% rated power and shoot for 10% max.

    #31 4 years ago
    Quoted from G-P-E:

    Limiting the charge current is definitely required there but still gotta watch for heat. That's 0.25 watts being dissipated by the current limiting resistor. Make sure to use a resistor -at least- 2x the anticipated power being dissipated. I normally don't like to drive a resistor at anything more than 25% rated power and shoot for 10% max.

    I used a 1/2w resistor. The power is 1/4w only if the capacitor is totally dead and then it quickly reduces as the capacitor charges. If the capacitor is dead, then the whole concept of a backup capacitor is not working anyway!

    #32 4 years ago

    For what its worth in my real world playing around. A 6264 ram holds data at 2v. Battery or cap under 2v and you start to get factory settings.

    A 5101 RAM holds data even lower. It will hold data at 1v and over. Also the 5101 RAM scrambles pretty slow. After 30 minutes of no battery, in a bally game half of the data will still be saved right.

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