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Author Topic: Battery Power: Running both Positive and Negative  (Read 2145 times)
W7DJM
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« Reply #15 on: March 10, 2005, 09:04:31 PM »

""Battery Isolators are the solution""

I'll even take issue with K7PEH, here.  

Even though I'm not a "professional mechanic,"  I've had my share of rods, winches, 4x4's, radios, etc.

I sold auto parts for over 15 years.

Here's the problem with isolators, and I've seen it TWICE in marine installations, and  more on someones trucks.

The isolator is nothing more than a pair of diodes.  Now, imagine that the one feeding the MAIN battery opens.   Now, the alternator "thinks"  that the main battery is dead, so it cranks up.   The second battery floats up to whatever the alternator voltage is, and starts to puke out acid.  Since the main now has no charging circuit, it keeps getting lower and lower, as the accessories draw it down,  The regulator tries to accomodate, and all that happens is, that the second battery keeps getting more and more overcharged.

The way to tie two batteries, in my book, is a solenoid called a "constant duty solenoid."  MAKE SURE that if you buy one that the parts "guy" knows what he's talking about and doesn't try and sell you a starter solenoid--it won't work--for long.
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K7PEH
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« Reply #16 on: March 10, 2005, 09:38:26 PM »

About battery isolators and supposed problems...

The previous post mentioned a problem if a diode opens.  I have looked at the isolator and if a diode opens then no current will flow to that side (that particular battery).  It will be as if it is not there.  The alternator will never see it and if anything is drawing current from that battery then it will just die a quiet death until the problem is fixed and the battery recharged.

So, this is the outcome if the diode opens to the battery that has been cut out.  For the other battery, you have a normal circuit between the alternator and the battery.  This other battery does not see the first "dead" battery so it is not affected by that problem.  Thus, in this case, everything is hunky-dory and no problems.

Now, I am not an auto-mechanic either and I am not an expert on these isolators but I have studied them a little bit.  I do have a degree in Physics so reading the technical specs and following the circuit flows is pretty easy first-grade stuff.

Now, if the diode did not open but rather there was a short in the diode that allowed the two batteries to see each other then you can get some inbalance in the charging and cause a bit of havoc by one battery being discharged while the other battery is being charged.  But, even in this case, there should not be any problem of over-charging unless there was some other flaw in the alternator circuit.

The diodes for these isolators come in different sizes but the larger ones handle up to 350 amps!  But, a charging circuit usually does not command that kind of high amperage so that would be an unusually large diode.

Also, battery isolators and multi-battery circuits are very common yet I have not read of any negative problems from the research I have done.  Does not mean that it does not exist but it may mean that it is not a common every day occurance.

Can there be battery problems?  Yes, in my previous truck my battery literally fell apart after about 10 years -- one battery for about 10 years and then one day the cell straps broke off due to degradation in the plastic.  Only real hassle on that is that my truck was parking in large mall parking garage with limited clearance and the tow truck did not have the ceiling clearance necessary to lift my truck up enough to tow out of the place.  We had to push my truck by man-power to an area where we had the clearance.

phil
K7PEH
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K0BG
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« Reply #17 on: March 11, 2005, 06:35:56 AM »

Phil, there is actually more than two diodes in a battery isolator, and what was posted previously is true. This very problem ruined a set of batteries in a powered sail boat that I installed radio gear in.

As for the relay, I don't like them myself, but lots of folks use them. Problem is, their more problematic than hooking two batteries together. I've been doing just that for years, and have never had a problem.

As I explained to you before, one of the major reason I run separate plus and minus is a noise abatement issue. I ground all of my mobile equipment to on ground location to help prevent ground loops caused by the various differences in resistance through out the body/frame of the vehicle. If you look at my web site, you'll see a picture of my 'tower of power' and you'll note there is a single ground tie point. To be sure, the unit is additionally grounded to the body at that point.

I appreciate Mark position of this, and while I agree with him that enough current might be passed through a fuse to cause damage before the fuse failed, if you take care of your vehicle in the same manner as you do your radio equipment, you shouldn't have any electrical problems, period.

I wish you luck in your pursuit to high power mobile. Just make sure the antenna you use can take the power too.

Alan, KØBG
www.k0bg.com
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K7PEH
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« Reply #18 on: March 11, 2005, 08:31:51 AM »

Where things stand today...

I have my appointment for all this work set up for next Wednesday (the 16th).  The only part that I am doing myself is that I am creating the antenna mount bracket in my shop since I can create exactly what I want to fit my truck and I am fairly adept at doing that sort of thing.  But, I hate actually working on or around cars and trucks so I am paying others to do the wiring.

This is the plan:

1.  I am running both hot and cold #4 cables from the battery to under the back seat of my crew cab truck.

2.  Both positive and negative will be fused at the battery.

3.  Under the rear seat of my truck I am having mounted distribution blocks (heavy duty to handle the current) for both positive and negative.

4.  Also at the negative distribution block under the seat I am running a grounding strap to the frame of the truck.  I have already verified that this frame is also strapped to the engine block (no little wire here).

5.  I am running my antenna coax cable out through a SO-239 style pass-thru connector in the floor of my crew cab.  I was going to go out the back but the installer at the Car Toys has done this before and they thought the floor was better because underneath it is actually protected somewhat from ground and weather effects.  I already have a weather seal (removable) solution for the outside.

6.  Besides the antenna mount I am doing myself, I am having the Car Toys guys install a grounding strap between the back bed of the pickup truck to the frame.  Right now it is not well grounded.

7.  My antenna mount is very heavy guage aluminum in an L-shape that will fit in the little tie-down type hole near the back corner of the pickup bed truck.  This will be grounded to the bed of the truck as well since it fastens to my antenna connector I currently have.  Until I decide upon a better antenna, I am going with cheap hamsticks.

I am not running with power yet.  The SGC 500 watt amp is a future thing.  I am going to go with this configuration to see how it operates and then consider the power and the extra battery.  I will probably go with the isolator.  Sure, it could fail but I doubt that they fail that often because if they did I would have been able to find that info.  It is more likely I might run into someone on the freeway and damage my truck that way.

One more thing.  I am running the audio output into my Bose 6-speaker system using the input jack designed for the XM Radio that my truck supports.  There is a device that is already setup for this sort of connection and I know another ham who has done this and he has had no problems.

The total estimated cost for the Car Toys work (almost all that I reported above) including all cables, fuses, distribution blocks, and so on is about $350.

Everyone contributing here has given me some good information and advice.  This is really a great forum and web site.  Will there be bugs to work out -- possibly.  But, I have been a computer programmer for about 35 years and fixing bugs is part of my life.  

When I am done I will probably take lots of photos and post them on my web site where I several other photo arrays already on previous projects.

phil
K7PEH
www.k7peh.com
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W7DJM
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« Reply #19 on: March 11, 2005, 08:40:29 AM »

""The previous post mentioned a problem if a diode opens. I have looked at the isolator and if a diode opens then no current will flow to that side (that particular battery). It will be as if it is not there. The alternator will never see it and if anything is drawing current from that battery then it will just die a quiet death until the problem is fixed and the battery recharged.""


I'm not just posting this to hear my keyboard rattle around, I've actually seen this problem, from customers that I personally know.  In  one case it could have been disasterous--marine bilges are no place for hydrogen gas.

Some alternators "sense" the charging voltage from the "main" battery, and so I say again--as the battery gets more and more  "dead"  from the normal running load, the alternator tries to compensate--overcharging the second battery, which  does NOT have a sensing circuit.

""I do have a degree in Physics so reading the technical specs and following the circuit flows is pretty easy first-grade stuff.""


You might want to take another look at that circuit.   When the MAIN battery diode opens, the vehicle/boat LOAD is still connected to the MAIN battery, and the MAIN starts to discharge.  

The alternator/sensing circuitry is all based toward this end--it normally is connected THROUGH THE KEY TO THE MAIN BATTERY, and so the MAIN is what is being sensed by the regulator.


Having seen the direct result of this, by means of spilled acid, ruined inner fenders, and a smelly Boat Bilge,  I think you can understand why I'm so adamant about it.    The company I worked for made an effort to carry "heavy duty"  "brand name" products in this area, and we even tried to get some ideas from the manufacturer.  

After these (several) incidents we began to strongly push "continuous duty" solenoids.   Back in those days, these solenoids cost about 12 dollars.   I understand now they can be over 20 or 30 dollars.
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K7PEH
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« Reply #20 on: March 11, 2005, 10:24:29 AM »

W7JDM --

>>>>>>>
I'm not just posting this to hear my keyboard rattle around, I've actually seen this problem, from customers that I personally know. In one case it could have been disasterous--marine bilges are no place for hydrogen gas.
<<<<<<<

Are you upset?  I take your comments seriously and I add them to my repository of information and your experiences just gives me more ammo for discovering the right solution and so on.  Therefore, do not presume that your efforts are not appreciated (..."keyboard rattle around").

The whole reason I posted my questions here is because I am in rapid learning mode on mobile equipment.  I have talked to a few of my ham friends that use dual batteries with isolators raive about that particular solution.  The dual battery thing though is really a solution in the back corners of my mind right now, it is not the main issue at hand so I have lots of time to learn more about the best solution in this area.
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K0BG
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« Reply #21 on: March 11, 2005, 10:28:25 AM »

Delar, I'm on your side with respect to isolators. The one in the boat I've been working on has two alternators, and three batteries. There are switches to switch between the main starting battery and the other two which are the accessory batteries. The isolator in this case uses 5 diodes as well a voltage divider to feed sense back to the alternators. When it failed (apparently due to a lightening strike) one of the diode shorted. This upset the voltage divider, which allowed the alternators to over change the main battery to the point it out gassed enough to set off the bilge fume alarm. The owner assumed the batteries were defective and replaced them only to have the same thing occur again. The new isolator has some built-in circuitry which is supposed to keep this from happening. Fat chance, as the forces of nature are not listening.

Incidentally, a 100% duty cycle relay with a capacity of 100 amps is just over $85 at our friendly marine supply. My only problem with relays and circuit breakers is their instantaneous maximum current ratings of about 3500 amps. A good marine or car battery will exceed that on a dead short with obvious consequences.

Alan, KØBG
www.k0bg.com
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KC2MMI
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« Reply #22 on: March 11, 2005, 12:33:05 PM »

Mark-
 <I too have ...instructions that show a separate negative lead...from auto manufacturers. ... if it works so great, why don't *they* do it that way? >

 Auto makers don't run separate ground leads because ground leads COST MONEY. Every vehicle you buy, including the luxury cars, is built to a price point and the cost of roughly doubling the amount of wires and wire connections, and the increased number of possible failures and warranty costs from that, is simply more than any customer would be willing to pay.

 Save $5 worth of wire on a million cars, and you've made $5,000,000 more profits for your division, and gotten a bonus. Build a car that costs $5 more than the competition--and you lose a million unit sales. That's the way their business works. Peak performance is NOT the motivating force behind mass-market goods like cars. "Good enough" is what they need to sell.
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KC2MMI
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« Reply #23 on: March 11, 2005, 12:40:17 PM »

Phil-
 <So, I need to handle peak draws of maybe 80 to 90 amps and an average of maybe 45 amps during transmit. Thus, I am using #4 wire. >
 By the time you get to 4-guage, that's called "cable" not wire. If no one told you yet, SAE and AWG guages are different by a full guage size, that is, #4AWG is the same size as #2SAE.
 But for 90 Amps, I think you'll find even #4AWG is undersized. You measure the cable run as a round trip, i.e. 20 feet to the trunk and 20 feet back is considered a 40-foot wire run. Using a typical wire chart that allows for a 3% voltage drop in a 12/14VDC system, I find a 2/0-AWG (not 00, but 2/0) cable is required for 90 amp loads.
 Yes, you can get by with less but you are going to be throwing performance out the window. Try to use something better than 4AWG even if your wire run is shorter. You can find guage/load charts like that all over the internet, just make sure if it is AWG or SAE and use it accordingly.
 And of course, you'll want fully tinned wire, with proper solder potted crimps on all the lugs. (That's the gun part.<G>)
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KC2MMI
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« Reply #24 on: March 11, 2005, 12:47:36 PM »

Rather than a battery isolator, look up "battery combiner". These are $100-150 boxes sold by West Marine (www.westmarine.com) for marine use.

Instead of isolating two batteries from one alternator with diodes, and losing 0.7VDC in the diode drop or modifying the alternator, the battery combiner uses a voltage sensing RELAY.

When the alternator is putting out +13.8VDC the relay closes (with a time-out to prevent chatter) and combines both batteries for charge/use. When the alternator puts out less than 13.8VDC, the relay opens and the batteries are isolated. You connect your radio gear to the AUX battery, and leave the car running on the main battery, or however you choose.

A very convenient solution.

Even more elegant is a Balmar or other marine alternator. They are available with dual outputs, so the alternator literally is monitoring and charging two batteries completely separately. This provides optimum charging on each battery, and total isolation of the systems when the alternator is not running. Balmar also sell external regulators which, again, provide optimal charging solutions for deep cycle batteries, i.e. they can be set for a fast recharge which AGM batteries accept, and car batteries don't.
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K7PEH
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« Reply #25 on: March 11, 2005, 01:11:35 PM »

Several comments:

On Battery Combiner thingy --- I have looked at that and have set aside the various web links of companies that make such things --  but none of the guys I know have one so it is still in the research phases of my efforts.

On Cable size --- Well, I do not know if this #4 is SAE or AWG but it seems to be a size that all agree is right for the load and the peak demand.  This "cable" including the insulation, is darn near 1/2 inch in diameter so it is not small.

The "Car Toys" people who are doing the install seem to be fairly experienced in this sort of thing.  Not only do they install power supply feeds for audio equipment that dwarfs the load demand of even my future 500 watt RF amplifier, they have done a number of ham radio mobile rig installs too.  I am not their first victim.  Plus, the lead installer whom I have been talking to on all these things owns the same kind of truck that I own and he did the wiring of his own truck and he is well versed in all the little gotchas that could come up.

Of course, Car Toys does big power audio and I just don't understand that.  I can sense these guys with 1500 watt amps approaching when I am at a stop light or in traffic.  The vibrations hit you first and then that deep low thump of the base speakers.  I mean, does this make sense.  OK, maybe it is my age.  My rock days during the 60s have done enough damage that my hearing now is not what it should be.  Do these guys know they will pay for this when they are older.


OK, my rant on big power audio is over but I still do not understand it.
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K7IHC
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« Reply #26 on: March 12, 2005, 01:03:14 AM »

Interesting in that you want to use an SO-239 type of pass-through for the antenna co-ax.  Why not just run the cable through a grommeted and sealed hole in the body?  I've done many mobile installations that way.  I think the extra connector could eventually be a trouble spot.

I have never run a separate negative wire to the battery for any mobile radio equipment power.  In twenty years, no problems.  I just make sure the battery connections and cables are well maintained and I use a single-point body ground for all the dash-mounted equipment.
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K7PEH
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« Reply #27 on: March 12, 2005, 07:31:57 AM »

K7IHC,

The reason for the pass-thru connector is that it makes it easy to remove the coax when I want to remove it -- which will be frequent.

If I run the coax through a rubber grommet then I basically have the coax permanently installed.  It is not easily removed because it has soldered on PL-259 connectors on each end.  So, to remove it I would probably end up having to cut the coax.  Thus, this is not supportive of what I want.

I doubt that I will have much problem with the pass-thru connector.  I got the idea from another ham in the area and he has had no problems.  In fact, he has three for three different antennas.

Apparently the battery power cabling issue is a true "discussion issue" worthy of many arguments of pro and con.  I have decided on both cables (positive and negative) just because I took in all the advice and made my decision.

Some might suggest approaches to these problems as money saving or maybe less elaborate due to cost.  Money is not the issue in my configuration.
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KA0GKT
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« Reply #28 on: March 14, 2005, 05:01:51 PM »

One good reason to fuse the negative lead to your transceiver is that it is possible that other devices could become grounded unintentionally through the transceiver.  For instance, you have that 160-watt VHF amplifier.  The ground lead comes undone, but hot the hot.  Now you have, perhaps as much as 20-30 amperes plus the draw from your transceiver going through a wire meant to handle less than half that amount.  With the fuse, you protect the wiring and perhaps the rig from destruction.

I am pushing 35 years in the electronics biz one way or another.  I cannot see a reason NOT to run your negative lead directly to the battery.  The chassis and body of your automobile is attached one way or another to the negative post of that battery.  Whether the return from your rig goes through a heavy black copper wire or the steel body of the automobile makes little difference safety-wise, but in terms of I/R drop, the copper wire makes tons of sense.

Do fuse both leads at the battery.  Consider running the hot lead through a coaxial capacitor sufficiently sized for your load and grounded to the firewall.  Carefully route the power cables to your transceiver along a route NOT used by other automotive wiring.  This is to prevent any RF which might be on the power cable from interfering with the operation of the vehicle.

Sound installers often use “Stiffening” capacitors to help correct for I/R drop problems in their high power sound systems.  These are large capacitor (some companies claim that they have a One Farad (Not Micro or Pico) {*Yeah, Right!} capacitor which takes some of the current load during loud transients, recharging through the I/R drop during quiet passages.  I haven’t considered the ramifications of using these devices for SSB or CW, however I am not too sure they would help much on full duty cycle modes like full carrier AM, FM, Digital and RTTY.

Good luck with your mobile install.

73 DE KA0GKT/7
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KA0GKT
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« Reply #29 on: March 14, 2005, 05:12:46 PM »

If you are concerned that your transceiver will become the return path for the starter or other high current automotive circuits, run a 1-0 (one-Ought) cable from the negative post of the battery to a plate bolted to the steering-wheel support under the dash (often there is a manufacturer installed small grounding plate at that location).  Solidly ground the new plate to the steering column support, the 1-0 cable to the ground plate and all of your Ham gear to the ground plate.  A low ohmic ground for your gear, and they are isolated from the possibility of backfeeding the starter or other high current devices.

Still fuse the negative leads for the aforementioned reason(s)

DE KA0GKT/7
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