Provista ISC3042

Submitted: Thursday, Oct 31, 2013 at 11:46
ThreadID: 104940 Views:9129 Replies:3 FollowUps:12
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I have a newly installed ISC3042 installed in a Mercedes Sprinter Motorhome with a 150watt (so far) solar panel and a separate AGM 100a/h house battery connected to the Original start battery via a BEP Voltage Sensing Relay.

On paper this regulator looks good as an MPPT 30 amp with separate adjustable bulk and float voltage adjustments.

After considerable research I found that Jaycar are marketing an identical model (except the colour) as an MP3735

My ISC3042 regulator shut down with an E5 error after running for a long drive (5hrs) with the fridge as the only load and this code does not appear in the handbook.

When I stopped (the battery was fully charged and on float at 13.6v) the voltage then drifted up to 16v and E5 with the motor/alternator off, I think the fridge had cycled off so no load was present. (E5 cuts the load anyway)

Quite a mystery, but the supplier has contacted the distributor and confirmed the regulator has a problem, so is replacing all their shelf stock as well as mine.

I can't help but wonder if it has the same firmware problem as mentioned in another post on the ISC3022 in August.

Will post my progress,


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Reply By: Herbal - Thursday, Oct 31, 2013 at 12:05

Thursday, Oct 31, 2013 at 12:05
According the intergooglewebthingy E5 means not enough sunlight to charge the battery.

Found it here -
AnswerID: 520669

Follow Up By: Kevin H5 - Friday, Nov 01, 2013 at 19:17

Friday, Nov 01, 2013 at 19:17
The unit came with V2 of the manual and when I searched I only came up with V2. The V2.1 manual obviously contains E5.

My unit clearly came up with E5 when in bright sunlight (19v from the panel) and a fully charged battery on no load. I have no idea what the extra 46 on the end of the 304246 means, mine is only a 3042.

Data on the Powertech M3735 (same regulator different label) states; "Note: An E5 error code is for Battery Over-Voltage Protection - This means the battery voltage is too high. Measure the battery voltage, and check if other energy sources are connected that may be driving the voltage too high."

When it failed it remained in Bulk mode whilst I watched the inbuilt voltmeter go slowly from 14.0 in steps to 15.9 then shut down with an E5 error.

The fault may have been caused by regulator not liking the no load status or the standard Mercedes Sprinter regulator holding the voltage above the float voltage for the extended period. I now monitor voltage constantly and it sits at 14.2 constantly.

The unit has now been replaced and works as expected, apparently it had a bug in the firmware.

Will provide a future update as I plan a drive the 1700km from our base in Mackay to Sydney and back this month and will monitor it closely.

FollowupID: 801227

Reply By: Eric Experience - Thursday, Oct 31, 2013 at 21:38

Thursday, Oct 31, 2013 at 21:38
This is interesting, how confident are you in your volt meter.? Can you measure the voltage on another car to check your meter? Where do you live? Thanks for posting. Eric
AnswerID: 520699

Follow Up By: Kevin H5 - Friday, Nov 01, 2013 at 19:23

Friday, Nov 01, 2013 at 19:23
I am based in Mackay QLD and an interesting quirk I have noticed with the standard Mercedes Sprinter connections (ie no house battery or solar connected) the voltage straight after start climbs to 15v for a short period then settles down to 14.1v.

The original voltage was monitored on the inbuilt meter confirmed against my DVM and now a DVM connected to the cigarette lighter on the dash and all agree to the same .1v including the new regulator.

FollowupID: 801228

Reply By: Eric Experience - Sunday, Nov 03, 2013 at 21:25

Sunday, Nov 03, 2013 at 21:25
Thanks for the reply. This means that your alternator is controlled by the ECU and not its own inbuilt regulator. This poses a problem if you disconnect the alternator from the ECU does the voltage become unregulated? Some poorly educated motor home builders switch the alternator to house batteries which could have bad results. Can you do me a favor and climb under your Sprinter and run your finger along the heavy wire that connects the alternator to the starter, what I want to know is there a fuse in the wire just below the sump near the flywheel? The way to fix your solar regulator problem is to connect your house battery to the alternator via a relay operated by D+. You then use the normally closed contact on that relay to connect your solar regulator, that way your solar regulator never sees the 15volts. Eric
AnswerID: 520807

Follow Up By: Kevin.Hutch - Sunday, Nov 03, 2013 at 22:22

Sunday, Nov 03, 2013 at 22:22
The batteries are connected via a BEP bydirectional VSR.

The new conversion is a Talvor (Brisbane) conversion with a wiring loom from connexwire in NZ, I only purchased it on 31JUL13 so still under warranty and the solar was installed by their recognised warranty agent in Mackay.

I have compiled an electrical wiring diagram, to the best as I can trace, to help diagnose the issue. I could not attach it, but could email in PDF format, my email is

The alternator wiring looks all original running under the flywheel in a protective rail and onto to the back of the battery box, whilst the wire to the VSR enters through a hole in the front of the case.

In the daylight tomorrow I will confirm your request and open up the battery compartment to confirm how the cable that goes directly to the battery compartment is connected.

FollowupID: 801370

Follow Up By: Eric Experience - Monday, Nov 04, 2013 at 21:25

Monday, Nov 04, 2013 at 21:25
I did not explain well enough. What I want to know is there a fuse in the heavy wire under the motor. You will not see it but if you run your finger along the wire you will feel a change in diameter if there is a fuse if it is smooth across the bottom of the motor then there is no fuse. As for the charging cct don't feel that you have to stick to what the motor home people say, you will find that they no very little and will welcome the information on the correct way to charge the battery. If you want to demonstrate the correct wiring just ask you Mercedes dealer for a copy of the Body builders instruction sheet, it will show the cct. Eric
FollowupID: 801434

Follow Up By: Kevin.Hutch - Tuesday, Nov 05, 2013 at 08:31

Tuesday, Nov 05, 2013 at 08:31
Thanks for you time Eric all was fully understood, just time has been at a premium this end.

I have a copy of the "Auxiliary Battery Retrofit Guideline" plus the "Body Builders Info Book" and other than the fact that I have a three terminal unit on the battery and the relays are under the right hand seat every thing looks the same.

The cable from the 180A alternator enters a purpose built cross member under the flywheel where the cable is full sealed in heat shrink.

There is a "bubble" that could easily be a fuse in the cable then it splits into two cables, one to the starter and one to the battery. This appears to be a "Y" junction and all appears original.

The lead to the battery enters the battery box from the rear and connects to a block that looks like a fuse block (no neg connection so it's not a relay) with three outputs (presume fuses) and all looks original, as it is sealed with a sprayed blue coat I did not remove it to confirm. There are two large red cables and one smaller connected to it (plus a black cable directly to the +ve battery terminal) and the smaller, possibly a 10mm2, runs with the negative through an additional hole (not original) in the side of the case, via a VSR, to the 100AH house battery under an extra motor home seat (all in flexible conduit of course).

This would appear as a classic installation (of which I have seen hundreds in boats) of two batteries paralleled via a dual sensing VSR so that the alternator and/or the solar charge both batteries when either is over 13.7v, disconnecting when under 12.8v.

The subject of "the correct way to charge auxiliary batteries" has raged for years and is the subject of many heated debates on many forums, but my concern is why the voltage after start runs so high.

FollowupID: 801449

Follow Up By: Eric Experience - Tuesday, Nov 05, 2013 at 20:59

Tuesday, Nov 05, 2013 at 20:59
Thanks very much for that detail description. All is clear to me now.
The reason the voltage is high at the start is to get as much charge as possible during a short run then the charge tapers of as the battery temperature rises. This is good design and Bosch have made allowance for it in the design of there auxiliary charging system, yes there are debates about charging systems and clearly the set up you have is not working. Bosch have led the world on auto electrics for over 100 years so I will back there designs against any local ideas. All you have to do to fix your van is to change the VSR to a normal 50 Amp change over relay energized from D+ with the solar on the normally closed contact. To easy. Eric.
FollowupID: 801495

Follow Up By: Kevin.Hutch - Friday, Nov 08, 2013 at 07:11

Friday, Nov 08, 2013 at 07:11
The setup I have is now working perfectly I am yet to confirm what the firmware problem in the regulator was, my money is on the fact that they never expected to see such high voltage from a car alternator.

My alternator voltage tracks up from a days start to 15v for a period then settles back to 13.6 in steps after a long run.

I am in full agreement with Bosch that an isolation relay is the best way to go for charging an auxiliary battery, connected directly to the battery as Mercedes/Bosch say, not to the alternator and it would need to be energised by the ignition auxiliary circuit or an oil pressure switch that is off when starting. (I have had 90 amp relays fail with flat aux batteries.)

When adding a solar charger and a mains charger then a duel VSR overcomes the start problem by detecting the voltage and when either battery reaches 13.7v it the switches on connecting the batteries in parallel so both get charged.

This keeps the start battery topped up and makes up for the radio and any the standard load that may be used.

I also agree that a boost straight after the start addresses sulphation problems and makes for regular start stop running that a delivery van may experience. Being retired, I did not realise that automotive electrics had moved out of the dark ages of just being a constant voltage regulator.

FollowupID: 801689

Follow Up By: Kevin.Hutch - Wednesday, Nov 13, 2013 at 21:22

Wednesday, Nov 13, 2013 at 21:22
Just to complete the discussion and save anyone else the anguish, I found the following quote on the OEM versions distributor's site.

"Note: An E5 error code is for Battery Over-Voltage Protection - This means the battery voltage is too high. Measure the battery voltage, and check if other energy sources are connected that may be driving the voltage too high."

The regulator looked so good on paper and now with the firmware update it should live up to the promise.

Now I Feel all is resolved plus I have a switch on the negative of the VSR to isolate the Main and Aux battery circuits if I have further concerns.

I am still monitoring the Sprinter battery and still see 15v soon after I start, maintaining it for some minutes before dropping back. Now I know it's not a bug but a feature I can sleep nights.

Next I plan to fit a Balmar Smartgauge monitor so I can truly understand what is happening.

FollowupID: 802074

Follow Up By: Eric Experience - Wednesday, Nov 13, 2013 at 22:31

Wednesday, Nov 13, 2013 at 22:31
There are two types of solar regulators. one type shorts out the panel when the voltage exceeds 14.2. This type is the most efficient because it does not have any resistance in series. The other type has a transistor in series and switches the transistor of when the voltage exceeds 14.2. You had the first type which can not be used in a vehicle unless you wire it as explained before. by changing to the second type you have lost charge. As mentioned before your system will not be optimum until you wire it correctly. VSR are popular with auto electric people because they are easy to install but they kill batteries. If you come to Melbourne I can fix the wiring for you. Eric.
FollowupID: 802081

Follow Up By: Kevin.Hutch - Thursday, Nov 14, 2013 at 07:18

Thursday, Nov 14, 2013 at 07:18
Eric, I believe your are saying to wire the house battery to a changeover relay so that it has either alternator or solar charge but not both when the motor is running.

The principle of either, not both sounds like a good idea but with microprocessor regulators I would not think this is necessary. It also ignores the start battery charge when parked to make up for the "normal" load of radio cab lights.

Surely the D+ is connected directly to the start battery and will be live whilst every the start battery is connected and what is wrong with connecting directly to the start battery via a fuse. After all this is what Mercedes say to do.

I too have argued with sparkies who wire the alternator to the house battery then via VSR to the start battery, (based on the premise that the house battery needs more charging and why subject a full start battery to the bulk charge voltages). The VSR switches on at 13.7v either way and off at 12.8v with a minimal load when not operated that over very extended periods could flatten a battery.

I now have the neg of the VSR wire via a switch that removes the VSR load from both batteries when switched off and leaves each battery to its own charging circuit and not constantly in parallel. Boats like my Sprinter live out in the sun anyway, rarely parked in shade.

The solar regulator I have is the same as the original MPPT 3042 with a firmware update and I understand it runs PWM when on float which is open circuit switching and the solar panel voltage of 19v would appear to confirm this. I have only seen the short circuit type regulator for use on wind generators and this requires a large dummy load resistor.

Back in the 60's we installed short circuit regulators in remote locations to load up the wind generator and prevent it from spinning it's blades off in strong winds, when the batteries were fully charged. Now days they have a mechanical feathering systems and mostly use PWM regulators.


FollowupID: 802089

Follow Up By: Eric Experience - Thursday, Nov 14, 2013 at 21:49

Thursday, Nov 14, 2013 at 21:49
I am sorry you do not understand how the system works. D+ is provided by Mercedes to operate the relay. You say you have the information sheet provided by Mercedes but you have not read it. You seem hell bent on keeping the poor system you have. Good luck. Eric
FollowupID: 802158

Follow Up By: Kevin.Hutch - Friday, Nov 15, 2013 at 09:36

Friday, Nov 15, 2013 at 09:36
Your right I do not understand how the Sprinter regulator works and I was unaware that there is a regulator with a separate output live only when charging, after the initial high voltage had settled. I am yet to confirm this.

We used to use the oil pressure switch to achieve the no load start.

I do accept your point of view, as I have had this discussion with many sparkies that disagreed with the design on various boats and Bosch did not encompass multiple source battery charging.

I do accept your explanation that the ECU raises the output at start time to 15v and then steps down to 13.6v as the batteries charge. I monitor this now on a regular basis. Without sensing current or battery temp this must just be time based in the ECU.

I have done 100's of boat wiring schematics over the years, my technical grounding began in the 60's installing battery systems for remote telephone exchanges including "non electronic no break systems", army signal corps telegraphs, mini computers for 16 years with UPS systems, V8 supercar electrics and telemetry, in later years on boats, plus remote marine radio repeaters both solar and wind powered.

One bareboat company had all its fleet worldwide setup with ignition switched relays often experiencing 90amp relay failures and I believe still does, whilst most in the Whitsundays have diodes or VSR controlled charging systems.

I do understand how my Sprinter is connected and the way I have it is identical to the way the information sheet says to connect it with the exception that I have a bidirectional VSR that switches when either the alternator or solar regulator reach 13.4v instead of only when the alternator produces voltage on the D+ output. I have installed a manual switch to disconnect my relay when I wish thus removing the 1.8mA standby current drain. The BEP 125a DVSR is a relay not a transistor switch so there is no voltage drop across it.

I consider this is superior to the D+ driven relay approach, with multiple source charging, as it allows the use of standard electrics when the motor is not running, knowing the solar or shore charger will charge the start battery, yet disconnect the start battery when the house battery gets below 12.8v. Commonly on boats auto bilge pumps are on the start battery.

The problem I had with the solar regulator was accepted as a design fault and corrected by un upgrade in firmware.

Kevin H

FollowupID: 802181

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