# cutting off charger with MiniBMS



## dladd (Jun 1, 2011)

Right now I have one leg of the AC input to my 120v charger running through an SSR like this, and the MiniBMS HVC output powers the SSR. I know it works, cause it's shut down my charger a few times when my 12v battery died and took out the MiniBMS.  

Now I'm upgrading my charger to a 220v, 30a capable charger, and want to keep the same basic method of cell level overcharge protection. I'm not sure exactly what method to take here, can I just get a higher amperage rated SSR and cut one leg of the 220v? Something like this? Or should I use a DPDT relay like this that will break both legs of the 220v circuit? What is the upside/downside of a relay like that vs. an SSR?

It's a Manzanita Micro PFC30, and I'd prefer to cut it off by killing the AC power coming in, rather than going through the internal regbus. In normal usage I don't expect this to ever happen, as I have a top balanced pack, plan to charge to 3.5v, and the MiniBMS cuts power at 3.6v. This direct AC cutoff is my safety backup.


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## Elithion (Oct 6, 2009)

dladd said:


> can I just get a higher amperage rated SSR and cut one leg of the 220v? Something like this? Or should I use a DPDT relay like this that will break both legs of the 220v circuit?


Either will work fine.



dladd said:


> What is the upside/downside of a relay like that vs. an SSR?


Reliability. The SSR has very good reliability, but would be damaged by a major disturbance (e.g.: lightning) on the grid. The relay will survive the major disturbance (which might kill the charger, anyway), but will degrade over use.



dladd said:


> In normal usage I don't expect this to ever happen


On the contrary, in normal usage, the BMS does turn on and off the charger regularly (actually, with the MiniBMS, it will go off only once per power cycle) as part of the balancing process. It is only when balancing is complete that the BMS keeps the charger on, and the charger current goes to 0. (Or some variation thereof).
Details about the 3 stages of charging.

If you use a relay, it will turn off at the end of charge, when the current is low, so it won't be subjected to much wear and tear.


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## EVfun (Mar 14, 2010)

When I was running a EV Power BMS, which is similar in operation to the MiniBMS, I didn't have the BMS regularly shut off the charger (I was even using the MiniBMS head board.) My intention was that all the shunts fired before the charger shut off, but none of the cells reached the higher voltage point that breaks the BMS monitoring loop. After getting the pack balanced the cells will all shoot up in a matter of minutes. The charger's automatic voltage regulation (I'm using a Manzanita Micro charger too) will keep the cells from rising much more and the charger should time out.


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## Elithion (Oct 6, 2009)

That tells me that your pack is well balanced, and that the charger is set for a bit too low a top voltage, or the MiniBMS is factory set for a bit too high a max cell voltage. That's fine. 

One day, though, as cell balance drifts, the MiniBMS will shut off the charger, and you probably won't ever notice. (That's one of the beauties of a BMS.)


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## dladd (Jun 1, 2011)

Elithion said:


> That tells me that your pack is well balanced, and that the charger is set for a bit too low a top voltage, or the MiniBMS is factory set for a bit too high a max cell voltage. That's fine.
> 
> One day, though, as cell balance drifts, the MiniBMS will shut off the charger, and you probably won't ever notice. (That's one of the beauties of a BMS.)


Yeah, with my top balanced pack, MiniBMS set to kill the charger at 3.6v, and a charger set to 3.5vpc (168v for a 48 cell pack) I've never had the MiniBMS shut down the charger except for when the BMS lost 12v power. That's in over a year and 10k miles. With the new charger I plan to continue with charging to 3.5vpc, so I don't expect it to behave any different. The relay is just a backup safeguard.

good to hear the SSR on one of the two 220v lines is good enough. On further inspection, it turns out that the one that I have in the car already is rated at 40a not 15a, so I'm good to go! sweet.


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## tomofreno (Mar 3, 2009)

EVfun said:


> When I was running a EV Power BMS, which is similar in operation to the MiniBMS, I didn't have the BMS regularly shut off the charger (I was even using the MiniBMS head board.) My intention was that all the shunts fired before the charger shut off, but none of the cells reached the higher voltage point that breaks the BMS monitoring loop. After getting the pack balanced the cells will all shoot up in a matter of minutes. The charger's automatic voltage regulation (I'm using a Manzanita Micro charger too) will keep the cells from rising much more and the charger should time out.


 That is the way I operate. The Manzanita timer is set for 15 minutes and the limit voltage is set to a pack voltage corresponding to about 3.44V per cell, about the bottom of the exponential part of the V versus Ah curve. If I do full charges regularly then most of the shunts are on by the time the timer times out (shunts turn on at 3.5 +/- 0.02V). If I do more partial charges, cells get more out of balance and only a minority of shunts will turn on when I do a full charge. After several full charges in a row I'm usually back to most shunts coming on. I've been doing more partial charges lately. Did a quick check of all cell voltages during the last few minutes of a full charge today and had two lowest ones at 3.450V and 3.452V, rest were 3.477 < V < 3.510, only 11 out of 36 were shunting. There is probably less than 1Ah difference between the lowest and highest so no concern for 180Ah cells, but I'll likely do some more full charges to get more shunts coming on. Note that some shunts come on as low as 3.48x V and others don't come on until 3.51x V, so I can have a bunch of cells at 3.490 < V < 3.500V and only some of their shunts will be on. 

I've had no problems running the above way, with charge currents from 7A to 28A, though I do have to tweak the limit voltage a bit summer to winter to get shunting for most of the 15 minutes.

I am turning off the charger with the regbus input.

I know Lee Hart has said that SSR reliability is dependent on the manufacturer, with cheap ones not as reliable in general, and he has had several fail shorted. I've been using a Magnacraft for over 3 years now on the pack connection to my DC/DC.


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## TEV (Nov 25, 2011)

dladd said:


> Yeah, with my top balanced pack, MiniBMS set to kill the charger at 3.6v, and a charger set to 3.5vpc (168v for a 48 cell pack) I've never had the MiniBMS shut down the charger except for when the BMS lost 12v power. That's in over a year and 10k miles. With the new charger I plan to continue with charging to 3.5vpc, so I don't expect it to behave any different. The relay is just a backup safeguard.
> 
> good to hear the SSR on one of the two 220v lines is good enough. On further inspection, it turns out that the one that I have in the car already is rated at 40a not 15a, so I'm good to go! sweet.


Probably you already know this, but just in case, make sure that the heat sink is big enough for the new amps.


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## dladd (Jun 1, 2011)

TEV said:


> Probably you already know this, but just in case, make sure that the heat sink is big enough for the new amps.


never assume I already know anything!  How much more heat are we talking about? The SSR is mounted to a pretty big steel plate which is about 6"x10". There's some heat now, but nothing serious.

here's a photo of it as it is now, you can see the plate that the SSR is bolted to (and other stuff is sitting on) which is in the trunk.


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## TEV (Nov 25, 2011)

Unfortunate, I have no experience with the SSR, I got one when I started my conversion but never use it, instead I have my Elithion Lite switching the Manzanita PFC40 by his BMS port. 

I read about people complaining about SSR failing but it seems that it happens because they don't use a proper rated heat sink.

You should search for your SSR , and find the information about what size heat sink it needs. I apologize for not being able to offer you more informations.


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## Siwastaja (Aug 1, 2012)

Doubling the amps will _approximately_ triple the heat produced in the SSR. If it is only slightly warm to touch now, it shouldn't pose a problem. If it's already very warm, it can become too hot. You see, the heat decreases the rating so if it's good for 40A at 25 deg C it may be good only for 20A at 85 deg C.

Is the 40A rating for continuous or peak, and is it at 25 deg C or 85 deg C?

I'd vote it's probably OK to use it, but would consider using a larger one just to add some safety margin. At least make sure your charge voltage doesn't cause immediate overcharging even if the charger fails on.


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## dladd (Jun 1, 2011)

Siwastaja said:


> Doubling the amps will _approximately_ triple the heat produced in the SSR. If it is only slightly warm to touch now, it shouldn't pose a problem. If it's already very warm, it can become too hot. You see, the heat decreases the rating so if it's good for 40A at 25 deg C it may be good only for 20A at 85 deg C.
> 
> Is the 40A rating for continuous or peak, and is it at 25 deg C or 85 deg C?
> 
> I'd vote it's probably OK to use it, but would consider using a larger one just to add some safety margin. At least make sure your charge voltage doesn't cause immediate overcharging even if the charger fails on.


Thanks for the info! This is the actual SSR I have, it doesn't seem to specify peak or continuous or anything. Just 40a, and -30C to 75C. I just ordered a heatsink to mount the SSR on, for ~$5 why not? Most of my charging will still be overnight at around 10a @ 120v, but sometimes I'll crank it to 20-30a @220v when I need a 'quick charge' or am using a public J1772 EVSE.

Tom and TEV, you are both using the Regbus for control, right? How are you implementing that? The HVC signal from the BMS is N.C., then opens to stop the charger. But the Manzanita charger requires a N.O. contact that closes to stop the charger. Do you use the HVC signal to trigger an external 12v relay that then wires into the controller Regbus? My concern about this is that if there is a 12v power failure the relay will stay in it's N.O. state and not kill the charger (leaving the pack unprotected by the BMS). It's a small loophole, but I'd rather have everything 'fail' into an off position instead of on.


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## Elithion (Oct 6, 2009)

dladd said:


> Regbus for control... How are you implementing that?


You need a SPDT relay. 
Connect the NC contacts to the Regbus. 
Connect the coil to the BMS.

The BMS will power the relay when charging is OK; the NC contacts will be open, and the Manzanita charger will be on.

If the BMS decides that the charger should be off, or if the power goes away, the relay coil will be de-energized, and the NC contacts will close, disabling the charger.

Like this.










Or like this.


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## TEV (Nov 25, 2011)

dladd said:


> Thanks for the info! This is the actual SSR I have, it doesn't seem to specify peak or continuous or anything. Just 40a, and -30C to 75C. I just ordered a heatsink to mount the SSR on, for ~$5 why not? Most of my charging will still be overnight at around 10a @ 120v, but sometimes I'll crank it to 20-30a @220v when I need a 'quick charge' or am using a public J1772 EVSE.
> 
> Tom and TEV, you are both using the Regbus for control, right? How are you implementing that? The HVC signal from the BMS is N.C., then opens to stop the charger. But the Manzanita charger requires a N.O. contact that closes to stop the charger. Do you use the HVC signal to trigger an external 12v relay that then wires into the controller Regbus? My concern about this is that if there is a 12v power failure the relay will stay in it's N.O. state and not kill the charger (leaving the pack unprotected by the BMS). It's a small loophole, but I'd rather have everything 'fail' into an off position instead of on.



Yes, I am using an external relay.

This is from the Elithion manual :

" Option 2: Control input

With this option, the BMS master controls the charger through a relay that disables or enables the charger.

Controlling the charger's enable input requires a relay for isolation. DO NOT CONNECT THE BMS MASTER DIRECTLY TOTOTHE REGBUS CONNECTOR!

Because of its polarity, the RegBus input is not fail-safe, so you need to take precautions: place the relay right at the reg-bus connector, and do your best to make sure that there is no way that it becomes disconnected from the RegBus. IF THE RELAY GETS DISCONNECTED, THE BMS WILL NOT BE ABLE TO PROTECT YOUR PACK! 

Control relay information

Relays can be "signal" or "power".

"Power" relays can carry a lot of current, but must be used with at least 1 A, or their contacts will quickly oxidize "Signal" relays do not need to be operated at minimum current, but are not available with quick-connect tabs.

In this application we need a "signal" relay, because we ask it to switch a very low current.

A typical automotive "cube" relay is nice because it is easy to mount and has quick-connect tabs. However, it only comes in "power" type.

We know that, in all likelihood, you will usea "cube" relay, which is not ideal for this application. So, we offer a workaround: add a capacitor (100 nF, 25V or more, any type) across the contacts of the relay; when the relay contacts are open, the charger will placea voltage across the capacitor, charging it; when the BMS master first energizes the relay, the contacts will close,quickly discharging the capacitor; the resulting pulse of current will clean the contacts, ensuring long lifefortherelay.

If you do use a signal relay, the capacitor isnot required, because the relay contacts remain clean even with no current. "


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## dladd (Jun 1, 2011)

OK, thanks. I get how it works now. So, are you guys using a 'signal' relay, or a power relay with a capacitor to trigger the regbus? I'm waffling now on whether I want to use the regbus input or a direct cut off of the incoming AC line. I've got a few days till I'll get around to installing it all, plenty of time to change my mind three or four more times. 

Charger just came in the mail today, pretty cool. You never quite know what you are going to get when you buy something in "new condition" on Ebay, but it has clearly never installed or even plugged in.


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## TEV (Nov 25, 2011)

dladd said:


> OK, thanks. I get how it works now. So, are you guys using a 'signal' relay, or a power relay with a capacitor to trigger the regbus? I'm waffling now on whether I want to use the regbus input or a direct cut off of the incoming AC line. I've got a few days till I'll get around to installing it all, plenty of time to change my mind three or four more times.
> 
> Charger just came in the mail today, pretty cool. You never quite know what you are going to get when you buy something in "new condition" on Ebay, but it has clearly never installed or even plugged in.


I use a signal relay, those have to be soldered on a board.


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## kennybobby (Aug 10, 2012)

Just a little nit-pick here but in the usa the 220(240)vac is a line-line voltage, not line-neutral as shown in the diagram--might want to check that this will work okay with the device since neutral is tied back to earth ground at the breaker panel.


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## Elithion (Oct 6, 2009)

kennybobby said:


> The 220(240)vac is a line-line voltage, not line-neutral as shown in the diagram.


Point taken. Also, for 220 Vac, you need two fuses. Only one is shown.
I will correct that drawing. 

However, the Lite's front panel does say "LINE" and "NEUT", which is important because the internal AC fuse is on the "LINE" side only. That we can't change.

Appreciated.


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## dimitri (May 16, 2008)

Elithion said:


> Or like this:


This is wrong. MiniBMS head board already has signal relays, so extra relay is not needed, just connect directly to the charger. The board offers both NC and NO pairs, so pick whatever your charger needs. 

Also, the picture shows old style board, which has been out of production for over a year.

MiniBMS user guide has up to date diagrams for several common chargers, if you take our diagrams and edit them, at least have the courtesy of getting it right


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## Elithion (Oct 6, 2009)

Sorry, Dimitri


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## dladd (Jun 1, 2011)

dimitri said:


> This is wrong. MiniBMS head board already has signal relays, so extra relay is not needed, just connect directly to the charger. The board offers both NC and NO pairs, so pick whatever your charger needs.
> 
> Also, the picture shows old style board, which has been out of production for over a year.
> 
> MiniBMS user guide has up to date diagrams for several common chargers, if you take our diagrams and edit them, at least have the courtesy of getting it right


Thanks for chiming in Dimitri! So, the board in that schematic (the old one) is the board I have. I'm not totally sure I understand which pin is which, could you let me know if I'm correct here? Here's a photo:










The three 'charger' pins (circled in red in my photo) are labelled a little oddly to me, but I believe the center pin is the common, the left (as you look at my photo) is the normally open pin, and the right is the normally closed. Right now I have B+ going to one side of my SSR, the other side goes to the common pin (center in my photo). The N.C. pin is tied to ground. 

For use directly on the Regbus of the Manzanita Micro charger, I believe I'd simply connect the common pin (center) to pin 1 of the Regbus, and the normally open pin (leftmost of the three circled pins) to pin 2 of the regbus.

Do I have that right? I must say your newer board is much more clearly labelled...

Thanks!
david.


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## tomofreno (Mar 3, 2009)

On mine _Charger_ (or HVC) and _Open_ (for normally open relay) are connected to pins 1 and 2 of the Regbus on the Manzanita. This applies 5V from pin 1 to pin2 if any cell hits 3.6V, reducing the charging current to zero. Here is some other info on the Regbus: http://www.diyelectriccar.com/forums/showpost.php?p=157262&postcount=9

Edit: the schematic in the minibms manual shows B+ and _Open_ connected to the "coil" side of an SSR to shut off power to the charger. Closed is tied to ground.


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## dimitri (May 16, 2008)

dladd said:


> For use directly on the Regbus of the Manzanita Micro charger, I believe I'd simply connect the common pin (center) to pin 1 of the Regbus, and the normally open pin (leftmost of the three circled pins) to pin 2 of the regbus.
> 
> Do I have that right? I must say your newer board is much more clearly labelled...
> 
> ...


David,

you are correct, see attached pic. 

Yes, labels on V1 board were confusing to many people, I apologize for that.


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## dladd (Jun 1, 2011)

tomofreno said:


> On mine _Charger_ (or HVC) and _Open_ (for normally open relay) are connected to pins 1 and 2 of the Regbus on the Manzanita. This applies 5V from pin 1 to pin2 if any cell hits 3.6V, reducing the charging current to zero. Here is some other info on the Regbus: http://www.diyelectriccar.com/forums/showpost.php?p=157262&postcount=9
> 
> Edit: the schematic in the minibms manual shows B+ and _Open_ connected to the "coil" side of an SSR to shut off power to the charger. Closed is tied to ground.


thing is, at least on the old board, it's a bit confusing because the pin labelled 'charger' is the N.O. contact, the pin labelled 'open' is the common, and the pin labelled 'closed' is the N.C. contact.


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## dladd (Jun 1, 2011)

dimitri said:


> David,
> 
> you are correct, see attached pic.
> 
> ...


awesome, thanks!


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