weldted Posted October 10, 2018 Share Posted October 10, 2018 Collected van from storage compound yesterday all batteries fully charged (Solar) Van been in my garage overnight not on ehu, eng battery reading 12.5 started up, engine battery 13.8 to 13.9 and stayed at that for ten mins at 1500 revs. Turned inverter on to power up on board mains charger engine battery volts went up to 14.4 turned inverter off again after a couple on mins eng bat voltage reading 13.8 ? Link to comment Share on other sites More sharing options...
keninpalamos Posted October 10, 2018 Share Posted October 10, 2018 and if you check it now what would you expect it to be? bearing in mind the van is still in your garage out of the sun. your readings seem pretty average to me. Depending on how much your alarm is consuming, if you have one I would expect the reading to be in the region of 12.7 and falling. Also using the battery to charge the battery via an inverter is a bit odd unless the inverter is powered by the leisure battery. why not use a battery to battery charger? Iv'e miss read or miss understood this somewhere I'm sure Link to comment Share on other sites More sharing options...
spirou Posted October 10, 2018 Share Posted October 10, 2018 He drives the inverter from the starter battery and uses it to power a secondary mains charger for the leisure battery. I don't know what the alternator is doing but something is weird :-D Link to comment Share on other sites More sharing options...
plwsm2000 Posted October 10, 2018 Share Posted October 10, 2018 weldted - 2018-10-10 7:54 AM .... Turned inverter on to power up on board mains charger engine battery volts went up to 14.4 turned inverter off again after a couple on mins eng bat voltage reading 13.8 ? How/where are you measuring the battery voltage? The inverter will probably be taking quite a lot of current and may introduce a small voltage drop in the battery ground or battery + wires so you may see slightly different voltages at different measuring points. Both the ground and battery + leads can make a difference. I cannot immediately see how you can get an increase in voltage under load, but your charger will also be putting back some current into the wiring and may be a factor. My other thought was if the measuring device was giving errors due to ripple on the DC power. An alternator generates an AC voltage that is rectified and regulated internally to give a DC output from the alternator terminals. As far as I know, there is little "smoothing" done inside the alternator, so the output will be mainly DC with a small amount of AC ripple superimposed on it.The ripple frequency will depend on the engine rpm and the ripple voltage will increase under high load. Depending on the shape of this ripple, different DMMs may give slightly different voltage readings. A simple way to check if this may be causing the effect is to switch the DMM to read AC volts. If the DC is "clean" (no ripple) it should read about 0Vac. At these frequencies, it will measure any ripple that is present on the power line. More expensive DMMs have a "true rms" function that is a more accurate and consistent way of measuring AC signals. Link to comment Share on other sites More sharing options...
aandncaravan Posted October 11, 2018 Share Posted October 11, 2018 Welted, excuse my 'Chemo addled Brain' but do I recall you have a Victron solar charger and Vanbitz battery master? If so that's is what will happen, the Vanbitz battery master won't necessarily charge up the Starter battery fully, explaining the Starter batteries low 12.5v initial voltage. Not only will it not charge it fully, but it will actively drain both batteries while in the garage. It is designed to permanently monitor both batteries, obviously drawing power from both as part of the monitoring process. Link to comment Share on other sites More sharing options...
weldted Posted October 11, 2018 Author Share Posted October 11, 2018 Following aandncaravan advice I removed the battery master when I fitted the Voltronic 350 mpp as this has the capability to charge the leisure batteries and trickle charge my engine battery, something that my previous controller couldn't. I am probably not the best at explaining. But it just made me curious that when my van having been brought home from my compound with presumably fully charged batteries and the solar computer showing 100%. After parked up for some 18 hours in my garage with no hook up or solar charging. That prior to starting the engine reading all from the computer were as follows. Everything off 12.5 when engine started 13.8/13.9 ran the engine at 1500 revs engine battery voltage stayed same. Turned on my inverter which is powered from my engine battery, to power up my Victron 30 amp charger and the ses fridge, saw the engine battery voltage climb to 14.4 ran this for ten mins or so dropping from 1500 revs to tick over voltage stayed at 14.4. Turned inverter off engine battery voltage dropped to 13.8. Only reason for these checks was having upgraded the batteries, solar controller, onboard battery charger and associated wiring just seeing what improvements to the charging system these mods make. As off soon for around six months. Link to comment Share on other sites More sharing options...
aandncaravan Posted October 11, 2018 Share Posted October 11, 2018 Hello Welted, sorry i obviously remembered the old set-up. I am not sure I understand what you perceive is an issue, if the Starter battery is a conventional after market Platinum style then it's voltage could be around 12.5 - 12.6v but if it is a Powerframe then about 12.9 - 13.0v. So your 12.5v is could be normal, depending on the battery? When you started the engine, depending on what was 'on', a 13.8v Alternator charge isn't unusual, as discussed in other threads and why using a setup like your 'mains charging from alternator 12v on the move' makes such a difference. When you turn on the Inverter to run from the alternator the mains charger should charge the Starter battery and habitation battery at 14.4v, so that is working as it should. But it will take a couple of hours for the batteries to recover to their normal state Of Charge, sometimes staying above 13v for a few hours. Link to comment Share on other sites More sharing options...
weldted Posted October 11, 2018 Author Share Posted October 11, 2018 Thanks Allan, I wasn't concerned that it was an issue just commenting on my findings, with the two new Youasa batteries although 100 amp against my previous 115 amp Excide, I find I am getting more bang for my buck. The voltage drop through onboard use is slower, recovery rate with the upgraded systems much quicker and very please. Just making sure the system wasn't chasing its tail. Link to comment Share on other sites More sharing options...
Alanb Posted October 11, 2018 Share Posted October 11, 2018 Weldted, If I remember correctly, you did not disable the original split charge relay, when you adopted what is in effect a home brewed B2B system. If the split charge relay is still connected, the voltage difference between the charger output voltage and the inverter input, will cause a large current to flow through through the split charge relay and associated wiring. Depending on where starter battery voltage is measured, this could result in a false high reading of the starter battery voltage. Alan Link to comment Share on other sites More sharing options...
aandncaravan Posted October 11, 2018 Share Posted October 11, 2018 Alanb, the mains Chargers are typically 300watt even with an 80% efficient inverter, it's typically only 25amps going into the habitation batteries at peak start up time, which reduces quite quickly as the battery charges. That is the very maximum you will ever see back feed. But because the voltage at the Alternator will also 'pick up' from the backfeed, the voltage difference reduces, further limiting any current going backwards. In reality the current is little more (plus the Inverter inefficiency) than would be drawn to charge the batteries anyway in a good, standard split charge relay solution. The Split charge relay contacts are so poor and the wiring so thin with so many connectors that current flow backwards is not what you might expect. It is those very limitations to current flow that led to this approach being explored. Link to comment Share on other sites More sharing options...
Alanb Posted October 11, 2018 Share Posted October 11, 2018 aandncaravan - 2018-10-11 3:28 PM Alanb, the mains Chargers are typically 300watt even with an 80% efficient inverter, it's typically only 25amps going into the habitation batteries at peak start up time, which reduces quite quickly as the battery charges. That is the very maximum you will ever see back feed. But because the voltage at the Alternator will also 'pick up' from the backfeed, the voltage difference reduces, further limiting any current going backwards. In reality the current is little more (plus the Inverter inefficiency) than would be drawn to charge the batteries anyway in a good, standard split charge relay solution. The Split charge relay contacts are so poor and the wiring so thin with so many connectors that current flow backwards is not what you might expect. It is those very limitations to current flow that led to this approach being explored. Allan, You seem to have failed to grasp the point of my post, and I do not understand the point that you are trying to make. While the inverter, and charger are non linear, the circuit through the closed split charge relay, and associated wiring is purely resistive. Ohms law applies and as I stated the voltage difference between the charger output, and the inverter input, will cause a current to flow back towards the invertor input. In these circumstances if Weldted's starter battery voltage is monitored close to the charger output, a voltage higher than that across the battery terminals will be indicated. On the other hand if Weldted's system has dedicated battery sensing wires then my explanation fails. In your final paragraph you seem to be agreeing with me in that there will be considerable resistance in the split charge relay and associated wiring. The current will flowing through this path, (probably a fractional Ohm resistance) will probably be several Amperes in order to produce the necessary voltage drop. Please note that Weldted was only querying an 0.6V change in the indicated starter battery voltage. I reiterate my statement that the inverter/charger combination, is in essence a B2B charger, but unless Weldted can confirm otherwise, the split charge relay is still connected. Alan Link to comment Share on other sites More sharing options...
weldted Posted October 11, 2018 Author Share Posted October 11, 2018 Re split charge? This is disconnected by a relay that operates when the inverter is powered up, the reason is this would prevent the daisy chain effect of the alternator Charging a battery powering an inverter powering a battery charger to charge the battery that supplies the power to the inverter etc etc. My system is that when the inverter is running it supplies the ses fridge 240 volt circuit and powers the onboard Victron 30 amp charger set to only send charge to the habitation batteries and not the engine battery. Likewise the same setup cuts out the trickle charge to the engine battery from the solar controller probably overkill the curse of a what if thought process. Link to comment Share on other sites More sharing options...
Alanb Posted October 12, 2018 Share Posted October 12, 2018 Weldted, Thanks for the info. Obviously, as you have disabled the split charge relay my theory fails. However I still think that your observed starter battery readings may have been influenced by where the voltage was monitored. (On the CBE system installed in my PVC the starter battery voltage is monitored within the 12V distribution board. When I added a CTEK D250S I added an external fridge relay which cuts the starter battery input when the alternator is charging. However an inncorrect voltage is displayed due to a back feed via the split charge relay.) I applaud your adoption of the "what if" thought process. This is what I employed when fitting the D250S. It resulted in 3 new relays, one of which was a 70A rating, used to cut the input to the D250S when on EHU, and hence avoid an unwanted input to output connection. Alan Link to comment Share on other sites More sharing options...
aandncaravan Posted October 12, 2018 Share Posted October 12, 2018 Alanb - 2018-10-11 8:30 PM Allan, You seem to have failed to grasp the point of my post, and I do not understand the point that you are trying to make. While the inverter, and charger are non linear, the circuit through the closed split charge relay, and associated wiring is purely resistive. Ohms law applies and as I stated the voltage difference between the charger output, and the inverter input, will cause a current to flow back towards the invertor input. In these circumstances if Weldted's starter battery voltage is monitored close to the charger output, a voltage higher than that across the battery terminals will be indicated. On the other hand if Weldted's system has dedicated battery sensing wires then my explanation fails. In your final paragraph you seem to be agreeing with me in that there will be considerable resistance in the split charge relay and associated wiring. The current will flowing through this path, (probably a fractional Ohm resistance) will probably be several Amperes in order to produce the necessary voltage drop. Please note that Weldted was only querying an 0.6V change in the indicated starter battery voltage. I reiterate my statement that the inverter/charger combination, is in essence a B2B charger, but unless Weldted can confirm otherwise, the split charge relay is still connected. Alan Alanb, I understood the point, but you said 'Large' current, I was pointing out the current will not be large because the chargers are usually low power and only peak for short periods of time. Overall the current will be less than it was in standard mode, resulting in lower voltage drop in the original cabling and a smaller difference between the 14.4v charger output and the real 14.2v'ish that the Alternatoer split charge will rise to due to the lighter load. Along with the more 'difficult current path' of the standard split wiring, little back feed takes place.. So while there will be some, it won't be 'large'. Link to comment Share on other sites More sharing options...
keninpalamos Posted October 13, 2018 Share Posted October 13, 2018 So, is this in effect a battery to battery charger? ie the engine battery is being used in a roundabout way to charge the leisure battery and if so, why? Is it gaining a big advantage over a Modern B to B charger and in what way, or is it just to see if it works. Link to comment Share on other sites More sharing options...
weldted Posted October 13, 2018 Author Share Posted October 13, 2018 Previously had a B to B charger. This setup gives me a charging rate of 14.4 volts up to 30 amps if required. Charging rate adjusts as required via my Victron charger. I have found this to be more efficient. It also allows me to run my large fridge freezer ses using 240 volt supply while travelling which is temp controlled and works better than the 12 volt element. Can use the microwave within limits, run a slow cooker and charge my Gtec multi when on the move. Though you are correct that it is a different version of a B to B unit but having had both I find this set up a marked improvement. Link to comment Share on other sites More sharing options...
aandncaravan Posted October 14, 2018 Share Posted October 14, 2018 keninpalamos - 2018-10-13 9:07 PM So, is this in effect a battery to battery charger? ie the engine battery is being used in a roundabout way to charge the leisure battery and if so, why? Is it gaining a big advantage over a Modern B to B charger and in what way, or is it just to see if it works. Keninpalamos, On many motorhomes it is the 12v load of the Fridge that introduces the biggest voltage drop on the charging system. Just removing the Fridge 12v Fridge load would improve Alternator charging of the habitation batteries. This solution does both, optimise charge to the habitation batteries and run the Fridge on it's most efficient, thermostatically controlled setting, unlike when on 12v when many Fridges are constantly on all the time you are driving. Link to comment Share on other sites More sharing options...
Alanb Posted October 14, 2018 Share Posted October 14, 2018 Weldted, You could also claim that it's a B2B made from existing units. One possible disadvantage that comes to mind is the added danger of having 240V distributed round the vehicle in an accident situation. A possible solution would be to trip the inverter via an inertia device such as that used to stop the engine after an impact. Alan Link to comment Share on other sites More sharing options...
weldted Posted October 14, 2018 Author Share Posted October 14, 2018 By putting the inverter output directly into the ehu socket the rcd will trip if a fault occurs, then the only live 240 would be a double insulated lead 1.5 mtrs long but point taken. Link to comment Share on other sites More sharing options...
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