Modules dying when 24V vehicles are jump started
in [Design]
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From: Tom Gootee on 3 Jul 2010 18:48 On Jul 3, 4:05 pm, n...(a)puntnl.niks (Nico Coesel) wrote: > Tom Gootee <t...(a)fullnet.com> wrote: > >We provide support for a number of systems installed in 24V vehicles. > >When the vehicles are not in use, the users like to leave the system's > >main power switch and circuit breaker both in the on position. If the > >vehicle then needs to be jump started, the users often do not first > >turn off the system's circuit breaker or power switch, despite > >continuing attempts at training them. Jump starting under those > >conditions tends to destroy a very expensive electronic module in the > >system. > > >Modifying the systems themselves is not a viable option. And we do > >not yet understand the exact failure mechanism that is occurring. We > >do know that there is an internal SMPS upstream from the at-risk > >module, but don't have schematics for the system. The system draws > >about 35 Amps continuously, when operating. > > >Knowing only that, is there something that could be strapped across > >the system's DC power terminals that would prevent damage from jump > >starting? Something available off-the-shelf would be ideal. If > >nothing already exists, what might work? > > I recall a similar problem. It turned out an inductor in series with > the power was causing overshoots on the power supply rail big enough > to kill an opamp. A big capacitor solved the problem. > > OTOH: in 12V automotive systems people usually design stuff to > withstand 60V (IIRC) spikes on the power rails. > > -- > Failure does not prove something is impossible, failure simply > indicates you are not using the right tools... > nico(a)nctdevpuntnl (punt=.) > --------------------------------------------------------------- Hide quoted text - > > - Show quoted text - Well, we probably have 20 feet of heavy wire between the system and where it connects directly to the vehicle's batterries. But our system is not drawing any current when the problem occurs.
From: PeterD on 3 Jul 2010 19:59 On Sat, 3 Jul 2010 12:52:10 -0700 (PDT), Tom Gootee <tomg(a)fullnet.com> wrote: >We provide support for a number of systems installed in 24V vehicles. >When the vehicles are not in use, the users like to leave the system's >main power switch and circuit breaker both in the on position. If the >vehicle then needs to be jump started, the users often do not first >turn off the system's circuit breaker or power switch, despite >continuing attempts at training them. Jump starting under those >conditions tends to destroy a very expensive electronic module in the >system. > >Modifying the systems themselves is not a viable option. And we do >not yet understand the exact failure mechanism that is occurring. We >do know that there is an internal SMPS upstream from the at-risk >module, but don't have schematics for the system. The system draws >about 35 Amps continuously, when operating. > >Knowing only that, is there something that could be strapped across >the system's DC power terminals that would prevent damage from jump >starting? Something available off-the-shelf would be ideal. If >nothing already exists, what might work? If you are using a connector to connect the jumper cables (like a military slave connector) you could rig a relay/contactor that would not allow power unless the switch was off.
From: Jim Thompson on 3 Jul 2010 20:49 On Sat, 03 Jul 2010 19:59:12 -0400, PeterD <peter2(a)hipson.net> wrote: >On Sat, 3 Jul 2010 12:52:10 -0700 (PDT), Tom Gootee <tomg(a)fullnet.com> >wrote: > >>We provide support for a number of systems installed in 24V vehicles. >>When the vehicles are not in use, the users like to leave the system's >>main power switch and circuit breaker both in the on position. If the >>vehicle then needs to be jump started, the users often do not first >>turn off the system's circuit breaker or power switch, despite >>continuing attempts at training them. Jump starting under those >>conditions tends to destroy a very expensive electronic module in the >>system. >> >>Modifying the systems themselves is not a viable option. And we do >>not yet understand the exact failure mechanism that is occurring. We >>do know that there is an internal SMPS upstream from the at-risk >>module, but don't have schematics for the system. The system draws >>about 35 Amps continuously, when operating. >> >>Knowing only that, is there something that could be strapped across >>the system's DC power terminals that would prevent damage from jump >>starting? Something available off-the-shelf would be ideal. If >>nothing already exists, what might work? > >If you are using a connector to connect the jumper cables (like a >military slave connector) you could rig a relay/contactor that would >not allow power unless the switch was off. There you go, a _proper_ solution... avoid the problem in the first place ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama: A reincarnation of Nixon, narcissistically posing in politically-correct black-face, but with fewer scruples.
From: Tom Gootee on 3 Jul 2010 21:22 On Jul 3, 7:49 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- Web-Site.com> wrote: > On Sat, 03 Jul 2010 19:59:12 -0400, PeterD <pet...(a)hipson.net> wrote: > >On Sat, 3 Jul 2010 12:52:10 -0700 (PDT), Tom Gootee <t...(a)fullnet.com> > >wrote: > > >>We provide support for a number of systems installed in 24V vehicles. > >>When the vehicles are not in use, the users like to leave the system's > >>main power switch and circuit breaker both in the on position. If the > >>vehicle then needs to be jump started, the users often do not first > >>turn off the system's circuit breaker or power switch, despite > >>continuing attempts at training them. Jump starting under those > >>conditions tends to destroy a very expensive electronic module in the > >>system. > > >>Modifying the systems themselves is not a viable option. And we do > >>not yet understand the exact failure mechanism that is occurring. We > >>do know that there is an internal SMPS upstream from the at-risk > >>module, but don't have schematics for the system. The system draws > >>about 35 Amps continuously, when operating. > > >>Knowing only that, is there something that could be strapped across > >>the system's DC power terminals that would prevent damage from jump > >>starting? Something available off-the-shelf would be ideal. If > >>nothing already exists, what might work? > > >If you are using a connector to connect the jumper cables (like a > >military slave connector) you could rig a relay/contactor that would > >not allow power unless the switch was off. > > There you go, a _proper_ solution... avoid the problem in the first > place ;-) > > ...Jim Thompson > -- > | James E.Thompson, CTO | mens | > | Analog Innovations, Inc. | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | Phoenix, Arizona 85048 Skype: Contacts Only | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon athttp://www.analog-innovations.com| 1962 | > > Obama: A reincarnation of Nixon, narcissistically posing in > politically-correct black-face, but with fewer scruples.- Hide quoted text - > > - Show quoted text - Thanks, Jim. I wish it were that easy. We could never get the users to go for that and we basically have no control over them. And remember I said they won't even follow the instructions to turn off the breaker before jump starting. But I did briefly entertain an idea for a sort of automatic switch at the system's 24V input, i.e. a relay that would disconnect the 24V line when it went below a threshold, and then have a fairly long time delay before closing it again when the voltage came back up. That would be a rather "jump start specific" form of protection. But the system would never be drawing much (if any) current when it was dis- connecting or re-connecting, which shouldn't happen a whole lot, anyway. So the relay contacts should stay good. But it seems like a TVS or Zener clamping circuit would be a lot cheaper and smaller, and maybe more reliable and robust, and should work well-enough. And they are available and ready to use as is. There are too many of these systems out there to spend a lot of money on each one.
From: Grant on 3 Jul 2010 22:57
On Sat, 3 Jul 2010 15:48:04 -0700 (PDT), Tom Gootee <tomg(a)fullnet.com> wrote: >On Jul 3, 4:05 pm, n...(a)puntnl.niks (Nico Coesel) wrote: >> Tom Gootee <t...(a)fullnet.com> wrote: >> >We provide support for a number of systems installed in 24V vehicles. >> >When the vehicles are not in use, the users like to leave the system's >> >main power switch and circuit breaker both in the on position. If the >> >vehicle then needs to be jump started, the users often do not first >> >turn off the system's circuit breaker or power switch, despite >> >continuing attempts at training them. Jump starting under those >> >conditions tends to destroy a very expensive electronic module in the >> >system. >> >> >Modifying the systems themselves is not a viable option. And we do >> >not yet understand the exact failure mechanism that is occurring. We >> >do know that there is an internal SMPS upstream from the at-risk >> >module, but don't have schematics for the system. The system draws >> >about 35 Amps continuously, when operating. >> >> >Knowing only that, is there something that could be strapped across >> >the system's DC power terminals that would prevent damage from jump >> >starting? Something available off-the-shelf would be ideal. If >> >nothing already exists, what might work? >> >> I recall a similar problem. It turned out an inductor in series with >> the power was causing overshoots on the power supply rail big enough >> to kill an opamp. A big capacitor solved the problem. >> >> OTOH: in 12V automotive systems people usually design stuff to >> withstand 60V (IIRC) spikes on the power rails. >> >> -- >> Failure does not prove something is impossible, failure simply >> indicates you are not using the right tools... >> nico(a)nctdevpuntnl (punt=.) >> --------------------------------------------------------------- Hide quoted text - >> >> - Show quoted text - > >Well, we probably have 20 feet of heavy wire between the system and >where it connects directly to the vehicle's batterries. But our >system is not drawing any current when the problem occurs. The 1.5kW are good for this, the unipolar ones are like a big zener, but with defined behaviour below the zener voltage, as well as the behaviour during the high current overload period. Use several in series/parallel. On 24V systems here I use 2 x 16V in series. On a motor drive system recently I had 3 x 16V in series for 48V turn on and they were getting warm! Dunno how you can measure spike suppression in your situation, so it's batter to put 2 or 3 times what you first think of in there. The TVS diodes are quite cheap, and are rated for repeat operation, unlike varistor type spike suppression. I suggest unipolar TVS diodes for your situation, probably multiple devices in parallel across the 24V power input. What's the highest normal voltage? The TVS voltage must be a little higher than that, then select number of then for the expected, plus some, overload power absorption. Follow the TVS devices with more spike suppression to reduce the high power voltage down to something your input circuit can handle. Watch the grounding to your thingy, as the battery return line will change voltage too -- this may affect other I/O lines connected to the unit. Grant. |