batteries, fuses, and jump starting

Not quite sure where to post this, but here goes... At work, we recently installed an asset management system on our fleet of heavy equipment (roughly 35 units). The system is from Trimble, and is basically a box with a GPS/Cell antenna that hooks into the ground, B+, and ignition hot. Normal current draw is <10 mA in sleep mode, and around 270 mA when transmitting info (once every hour). Recommended install procedure is direct to battery for ground (due to master switch...) and 2 A fuse to battery for hot. Right now, we're going broke replacing batteries (most sets are pretty old). I think we're at 12 sets in the 2 months since the install. I don't mind replacing old batteries, but some have been pretty new (less than 1 year old on frequent use machines). Doesn't seem like that current draw would kill a good set of batteries? The other issue comes when jump starting dead machines...it blows the fuses every time. Only thing I can guess is that stray current is trying to complete to ground through our box? Any way to prevent that? Thoughts and comments appreciated...2007 Dodge Ram 2500 Quad Cab, Cummins Diesel, 6 speed, 4x4

Why is the unit connected to B+ and not the vehicle battery itself? (Not that it should matter - but normally a quiet source is used for electronics.) The max 270mA is equivalent to a 12V 3W bulb, or 24V 6W bulb. That might be a concern after several days of not charging, but I suspect less than a 1:100 duty cycle so it should be several hundred days. I assume by batteries you mean the vehicle batteries.... Is it a 12V system system that is in a 24V vehicle? (To B+ - probably not!) If so, is the 12V wired across one battery or both? (That could be the problem - uneven discharge rates but the same charge rate.) Jump starting blowing fuses - you mean the 2A IGN fuse? And I assume your master switch is a ground switching system? (Yay! So many use hot switching. Then again when competitions confuse and combine kill & isolate switches and fail to define what needs NOT be isolated, I'm not surprised...!!!) Sorry for the questions, but it saves lengthy conditional answers. Though maybe someone with the right experience has the answer...?

A little different than the average prius; but electrical nonetheless. All the machines are CATs, most are 24V with 2 - 12V batteries. GPS unit will operate anywhere from 9-32V. Gotta have hot all the time so it can 'wake up' and report every hour or so. All ground and constant hot connections are direct to the battery(s). Ignition sense comes from a 10 psi oil pressure switch. Jump starting blows the constant fuse, sometimes the fuse to the oil switch. I don't know exactly what process they use to jump these things, but I don't understand how it blows these fuses like it does...it doesn't blow any of the oem fuses? Doesn't seem like a voltage spike would do it...has to be stray current, right? Master disconnect is on the negative side...pretty slick setup really,2007 Dodge Ram 2500 Quad Cab, Cummins Diesel, 6 speed, 4x4

Cool. When you said B+ you meant Battery+ as opposed to the B aka B+ terminal on the alternator. (IE - the heavy connection to the Batt+ which may have a fuselink, or not, or an ammeter on older vehicles when people though ammeters did something useful.) The B+ & Batt+ are the same electrically - except when considering voltage drops, or interference (the battery is like a big capacitor that filters the 3-phase alternator output and other spikes). I suspect the fuse blowing is from the unit being Batt- connected instead of chassis/ground. Something tells me "that's obvious", but I want to think about it before embarrassing myself yet again. (Then again, there is a first for every site LOL! Nah - overheating car-audio amps with higher impedance speakers is a red-Faces contender.) I was going to suggest the heavier "Big 3" - or at least one of them - but the isolation switch may be a limiting factor. What about jump starting with the isolation switch open, and connecting it after it has started? That might be better if the jumper battery was disconnected before closing the switch, but that means running without a battery which should be ok for modern alternators (with inbuilt regulators) - except for "battery filtering" - but might be risky anyhow. The reason for the open isolator with the jumper battery connected is that it may be the HUGE current from the jumper batt to the flattey (vehicle's flat battery) that blows the fuse(s). The alternator won't have the same current capability. Do you know if the fuse(s) blow when the jumper battery is connected, or when cranking? And how is it jumpered: to batt+ and chassis, or batt+ and batt- ? And then the is isolator closed? And then ignition on? I probably only need a few minutes with paper & pencil.... And I reckon then I can tell you how they are being jumpered.... I feel it's so obvious. But that's the art of procrastination - discussing possibilities instead of doing them. I'll hunt for a pencil. Otherwise maybe my feline Ms Claws will give me one from Santa Claws.... BTW - I don't want to change the ground isolation. IMO hot-isolation should be banned from competitive sports (they drag a high-current cable into the cookpit to a dash mounted isolation switch!!), but until they figure that out for themselves....   (It took them several years to "accept" the legitimacy of ground isolation down here!) And maybe they will insist on separate "kill" switches (which can be activated by a isolation switch). But we'll probably need a few more deaths first...

OK Mr. Tracker face here. We've had numerous problems with the TRACKER batteries after 2 years. They swell and bash against the modem cover disturbing the SIM. The at rest draw on our units is 34milliamps, couldn't even measure the draw across the ignition circuit. Ours like yours are 9-32v, but we've never had a flat battery on the vehicle. Sabotage:- With commercial vehicles, our fleets average 1 driver in 10 messing around. Usual trick is a blown fuse, I've found evidence of nicked cables etc etc. P.S. I'm thinking along the lines of fuses being destroyed by jump starting.

And here I thought it was the vehicle battery needing replacement.... If it's the unit batteries, it's a case of bad batteries or bad charging regime etc - they shouldn't really be used that much, but irrespective of that, IMO should certainly last longer.    As to blowing fuses, what order are things being done? If you: 1. IGN on; 2. close Isolator switch; 3. Connect jumper battery.... ... does the fuse blow? (I reckon it won't.) FYI - The above is courtesy of Gin&Tonic #4 on day #6 of my unscheduled beach holiday (a break between surf & New Decade activities). As I recall, the solution was easier than trying to confirm the connectivity. I think the order of #1 & #2 is unimportant. What is important is connecting the jumper battery LAST. (And as always, connect the last jumper battery connection on the upwind terminal on the jumper battery. So many still believe that "connect -ve last" crap.) PS - I'm currently or voltingly on G&T #2 trying to duplicate my Day#6 G&T#4 logic. That may have caused the joke in the last parenthisesed 2 sentences above.

My latest theory is that we should have wired them up differently. Right now the units are only to the battery that is grounded to the master switch (12v). This is causing significant strain on that battery, and as it falls below 9v, the threshold of the gps unit, the unit draws more than 2 amps and blows the fuse. Needless to say, we are moving the hot over to the other battery so it is drawing from both evenly (24v). Am I correct in thinking that this will also cut down the amperage draw of the gps unit by doubling the voltage? Some of our guys are pretty old school; I can't begin to understand exactly how the are jumping these things. I did one myself and didn't have any trouble with the fuse, so that's why I'm thinking that the fuse issue is related to the battery drain issue not the jumpstarting...2007 Dodge Ram 2500 Quad Cab, Cummins Diesel, 6 speed, 4x4

You should never draw a 12V load from one of the batteries in a 24V system - that will lead to premature failure of the 24V batteries. Make sure the units are connected across 24V (assuming they accept that as you previously indicated). Their current may double (resistive load), remain the same (current load), or drop (power load). Maybe others know what circuitry they employ. After connection across the 24V supply, let me know if the fuse blows with ignition and isolation "on", and jumpering last.