Battery equalizer

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Getting the bus ready for I trip,I realized that I may have a problem.I have a 97 h45/98 vantare/when I purchased the coach the top post on the blue round multi battery isolator mod 3002,had no cable on it,and the center post had 3 cables/bringing the coach home,over 2000 miles I had both high and unbalanced lights on the dash/I didconnected the 3rd cable from the center post and drove home/with the disconnected cable that appears to go to the house batteries reading 15.5 volts/the house batteries read 13.5 in float mode/the bus batteries read 12.5 as do the center and lower post on the surepower ind. isolator/where am I getting 15.5 volts from?If I hook up the cable with 15.5 to the top terminal,will that cook the batteries?Is there any way to test the battery isolator?with nothing attached to the isolator top post it reads 12.0 when the bus batts read 12.5 as do both the center and bottom posts on the isolator,which are hooked up currently/hope someone out there can help/thanks in advance/joe

[Jon Wehrenberg]

Red,

The isolator center is the alternator post. The top and bottom are for the house and chassis, or a second house circuit. I am not familiar enough with Vantare to know what exactly you have. Having 12 volts at the isolator tells me the chassis has its own alternator and does not go through the isolator.

The purpose is to keep either set of batteries from draining the other set while allowing the alternator to charge them both. In other words power can flow from the alternator to both sets, but it cannot flow from one set to another.

It sounds like someone has gotten creative and hooked it up as you described to defeat the isolator's piurpose. But regardless neither set of batteries should see a different set of voltages. The alternator output voltage is what each set of batteries should see. There is nothing to create a difference in voltages. If 15 volts is the alternator output it is to high.

To sort out this puzzle help me understand what you have back there. Do you have two alternators? You should have 24 volt coming from somewhere for the chassis. If you have two alternators what are they, their output, and what if anything are they going through (such as the isolator) to charge the batteries?

Do you have a single house circuit, is it 12 or 24 volts or do you have a 12 and 24 volt house battery system with batteries wired in series and parallel?

Once your coach set up is better understood answering the questions is easier.

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Jon/thanks for getting back to me/I have only one alternator,and the batteries are series and parallel/what I do not understand is why the 15 volts?the alt. is not running as I am on shore power parked/I can start it and check what the alt. output is/I checked the house batts/not running/ 12.5 and the house on inverter float13.5/if I was getting a 24 to 27 or 28 volt I would be reading the series batts/ house 2x 13.5 or bus 2x 12.5/I may have to trace the cable back to it,s source/any way of telling if the isolator is working? thanks joe

[Jon Wehrenberg]

Joe,

If you only have one alternator, likely the 50DN it is putting out 24 volts (nominal). With the engine running it should be in the range of around 27.75 volts, and you should have that voltage at both the top and bottom posts on the isolator.

I have no clue why someone joined the alternator, chassis and house cables at the center post on the isolator. I am guessing someone thought the isolator had failed. As it is wired now your house and chassis batteries are merged so as one set is drained the other is as well.

If I were to start trying to figure it out I would first check the isolator voltages with the engine running at the top and bottom and compare the values with the center post. Assuming all values are equal I would reconnect the house and chassis cables to the top and bottom posts. There is a procedure for checking the operation of the isolator. Gran Tracy may remember it or have it close at hand because I remember we checked his once. I don't remember it. Perhaps Ben, Gran or someone can jump in here with help on checking the isolator operation. The principal is current can flow in one direction, but not the other. An ohm meter can do that check, but I think there is a little more to the check than that but I cannot remember.

For the moment a quick way to check the health of your current battery voltages is to measure the voltages at the Vanner equalizer. Obviously with everything tied together at the isolator center post you should have the same reading on both equalizers. It should not matter if you are on shore power, generator power, engine running, or engine off because from your description they are all tied together. If the isolator checks out there is no reason to not separate them and connect them as they should be.

I am at a loss to explain why you would get 15 volts. Once you resolve the isolator question then I would suggest you check inverter output unless you get that voltage out of the alternator. Regardless of the reason for 15 volts, if in fact something is putting out that voltage it needs to be corrected. You should not have 15 volt output from any source. It doesn't make sense.

[BenC]

Getting the bus ready for I trip,I realized that I may have a problem.I have a 97 h45/98 vantare/when I purchased the coach the top post on the blue round multi battery isolator mod 3002,had no cable on it,and the center post had 3 cables/bringing the coach home,over 2000 miles I had both high and unbalanced lights on the dash/I didconnected the 3rd cable from the center post and drove home/with the disconnected cable that appears to go to the house batteries reading 15.5 volts/the house batteries read 13.5 in float mode/the bus batteries read 12.5 as do the center and lower post on the surepower ind. isolator/where am I getting 15.5 volts from?If I hook up the cable with 15.5 to the top terminal,will that cook the batteries?Is there any way to test the battery isolator?with nothing attached to the isolator top post it reads 12.0 when the bus batts read 12.5 as do both the center and bottom posts on the isolator,which are hooked up currently/hope someone out there can help/thanks in advance/joe

There is, with all cables disconnected from the isolator to test...basically just like a huge diode. From the center post with neg (black) lead of a digital multimeter, you should get approx .707kohms on the diode/2k ohmmeter scale. Then reverse the leads, put red on the center and the black lead on each top, then bottom post, it should give you a reading of infinity/open if the diodes are all good. Also, from outside post to the other outside post, in both directions the meter should read infinity/open circuit as well. Just like any diode, there is a voltage drop across the PN junction with current flow, so in a normally working system the alternator post/alternator output is 1-2 volts higher than each of the output posts that go to each battery bank to compensate (remember, the voltage regulator is "seeing what the actual chassis battery voltage is, not alternator output, and adjusting the alternator field to maintain the batteries at it's setpoint level). What is the 8th digit from the right and the last four numbers of your VIN, if you don't mind my asking? All Vantare H3's in this vintage should have 24-volt house batteries. Just curious.

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Ben/I am traveling today so will have to look up the 8th diget/coach is number 1855 and it has 4 gel cell 12 volts on each side over duels/I checked each battery/disconnected/individually and they were all around 12 plus volts/batts are 08 vintage.In float on inverters with batts hooked up the reading is 13.5. I will try the ohm test tomarrow when I get home/the 15 volt reading comes from the disconnected cable that I believe comes from the post that would attach to the isolator,and goes accross to the house batteries.It is a 98 vantare 97 h45 chassis/joe