Okta
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Don’t forget that any existing split charge relay will need to be neutralised when a B2B is fitted, otherwise you will have a feed back loop.
Help! Is my EHU actually charging my batteries?
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wildebus
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It is very simple to disable the split-charge relay in the EC155. You just remove the D+ Input into it.I'm mapping this really useful thread to my situation. A key message in later posts is that Sargent are good for power distribution but not for charging so add separate charging units. I have a 5m campervan so space for mounting equipment, especially in ventilated space is really tight. I can see how converters are attracted to the EC155 as it purportedly meets the relatively small needs of a campervan but as this thread shows it does not do this well. Moreover, it is not Lithium ready, an obvious battery upgrade for compact vans wanting to improve off-grid capability.
I really don't have the ventilated space for a separate DC-DC charger, larger solar controller, and EHU charger so now I feel conflicted:
Grateful for any help with this decision.
- Research a single box to replace the EC155 or compromise on one or more of the charging sources (EHU would be the obvious compromise)?
- Then what if in the future Lithium looked like the way forward, get a new van?
- Use the boss's clothes storage?
Apologies for highjacking the OP's question but this seems a natural progression so hoping it does not violate etiquette.
B2B chargers do not have to be that large physically and don't all have (or need) fans for cooling. The Ablemail AMC 30A unit uses passive cooling with the casing acting as a heatsink for example.
mistericeman
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I utilised the wardrobe wall for our electrical upgrades as most of our electrics were in the base or close by ...I'm mapping this really useful thread to my situation. A key message in later posts is that Sargent are good for power distribution but not for charging so add separate charging units. I have a 5m campervan so space for mounting equipment, especially in ventilated space is really tight. I can see how converters are attracted to the EC155 as it purportedly meets the relatively small needs of a campervan but as this thread shows it does not do this well. Moreover, it is not Lithium ready, an obvious battery upgrade for compact vans wanting to improve off-grid capability.
I really don't have the ventilated space for a separate DC-DC charger, larger solar controller, and EHU charger so now I feel conflicted:
Grateful for any help with this decision.
- Research a single box to replace the EC155 or compromise on one or more of the charging sources (EHU would be the obvious compromise)?
- Then what if in the future Lithium looked like the way forward, get a new van?
- Use the boss's clothes storage?
Apologies for highjacking the OP's question but this seems a natural progression so hoping it does not violate etiquette.
Started off with a Ring RSCDC30 to go with the 400w panels ...
That soon failed on the solar side (goes to sleep at dark and doesn't wake with sun)
Though still working as B2B charger OK ...
Solar regulator is now Victron as is,most of the other stuff including mains charger for wintertime to charge our 3 x 100ah agm batteries .
It's got to be said manufacturers must expect most motorhomes to be just parked up on hook up by the looks of the poor systems fitted .
merl
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Yes, you're correct Kev and not accurate information I'm afraid.
Sorry OTKA but you really need to brush up on ohms law.
The alternator get's first dibs on the Cab bat voltage because it's internal resistance is lower than the Leis Batt res plus the wiring res.(cabling, contacts, etc)
Pudsey Bear
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merl
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ONLY if you back ME up when me and the missus have our annual domestic about how a room thermostat works.Heck, can I have that in writing to show Liz
Pudsey Bear
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Annual, pussy, you need to make much more effort, I'm up to weekly now and we can go at it on any subject too, PMS has nothing on Liz.ONLY if you back ME up when me and the missus have our annual domestic about how a room thermostat works.
You'll have woken that bloody Trev up now, he'll be telling you how much you can save if you just turn it up and leave it on.
Okta
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You will need to convince me. In the scenario I am describing the smart alternator has shut down having got the engine battery to say 12.5V. The leisure battery is well charged and holding 12.8V. The split charge relay effectively puts the 2 batteries in parallel and the voltage difference causes the current to flow from the 12.8V leisure battery to the 12.5V engine battery.
In 2015 I bought a Mercedes based motorhome with a smart alternator. I found that when I started a journey with a fully charged leisure battery it always ended up less than fully charged at the end of the journey. I researched the problem, added a B2B and the problem was solved.
merl
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Hi, Hmm, I know what you mean so the following is written with an inquisitive tone, NOT an argumentative one. (being misunderstood has got me in trouble previously!)
So I'm just trying to work out under what conditions and for how long you'd have 2 batteries in parallel (1 with a couple of tenths of an ohm cable resistance in it's circuit) connected to a smart alternator and the smart alternator not taking care of their maintenance based on the voltage it's 'seeing'. Surely the alternator predominantly 'sees' the cab battery (the hab has wiring resistance added so wont affect the mix) has to keep the cab battery charged and maintained and the hab battery simply piggy backs off of this voltage source. So if the Cab bat is being charged and maintained (getting first dibs in my previous post) then the hab bat is also charged and maintained via the shunt.In reality how long does the Cab battery sit at just 12.5V for? There's a SA on our car, I have a cheap voltage monitor plugged into the fag lighter and because it's a SA the voltage fluctuates a lot, however I've never seen it sit at 12.5v for any length of time, just for a few seconds after starting and that's it, it's then back up to typically much higher voltage than a resting fully charged hab battery and no current will flow from hab to cab.
12.6V is typical resting voltage for a fully charged LA battery, 12.8V suggests it's recently come off EHU and it's voltage is still naturally falling to 12.6v anyway so the voltage drop you saw could have been that? Maybe your fridge was on/set to auto and the voltage at the Cab bat (even though it was higher than 12.6V) wasn't high enough to keep up with demand considering the wiring resistance?
Even if it WERE possible:
12.6V hab battery connected to a 12.5V cab bat give a potential difference of just 0.1V. 0.2 ohms wiring resistance (I'd guess it's be more but let's go with that) gives just 1/2 an amp of discharge current falling to zero when the cab batt reaches 12.5V
I know there are issues with SAs and hab battery charging but I genuinely cant see (at the moment) how a hab battery could get significantly discharged by one.
Merl
Pudsey Bear
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It's not called Electrickery for nothing Merl
wildebus
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BTW, if you want to get the leisure battery charging via a relay when you have a smart alternator there is a little trick you can do .....
Turn on the headlights
The starter battery does virtually nothing other than start the engine so any kind of significant electrical load and the alternator operates in a normal way to drive them.
Turn on the headlights
The starter battery does virtually nothing other than start the engine so any kind of significant electrical load and the alternator operates in a normal way to drive them.
Pudsey Bear
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Not sure what my 07 Duke has.
merl
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Well it's Italian so probably a manky old magneto!
Chrisinchip
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A thought ... maybe it is not so much about what conditions cause the current to flow from hab to cab but how low the smart alternator will let the voltage (assuming of both batteries) go before starting to charge, and then will it fully charge or just enough? I'm wondering if the state of charge upon arrival becomes a lottery, not so important for the cab but a real disadvantage for the hab, and pretty upsetting if it was at 12.6V resting volts at home.Hi, Hmm, I know what you mean so the following is written with an inquisitive tone, NOT an argumentative one. (being misunderstood has got me in trouble previously!)
In reality how long does the Cab battery sit at just 12.5V for? There's a SA on our car, I have a cheap voltage monitor plugged into the fag lighter and because it's a SA the voltage fluctuates a lot, however I've never seen it sit at 12.5v for any length of time, just for a few seconds after starting and that's it, it's then back up to typically much higher voltage than a resting fully charged hab battery and no current will flow from hab to cab.
12.6V is typical resting voltage for a fully charged LA battery, 12.8V suggests it's recently come off EHU and it's voltage is still naturally falling to 12.6v anyway so the voltage drop you saw could have been that? Maybe your fridge was on/set to auto and the voltage at the Cab bat (even though it was higher than 12.6V) wasn't high enough to keep up with demand considering the wiring resistance?
Even if it WERE possible:
12.6V hab battery connected to a 12.5V cab bat give a potential difference of just 0.1V. 0.2 ohms wiring resistance (I'd guess it's be more but let's go with that) gives just 1/2 an amp of discharge current falling to zero when the cab batt reaches 12.5V
I know there are issues with SAs and hab battery charging but I genuinely cant see (at the moment) how a hab battery could get significantly discharged by one.
Merl
I also wonder if the hab will never be fully charged because on the charging cycle the voltage across the hab will always be less than the cab because of wiring volt drops and naturally the smart alternator is sensing voltage at the cab.
Okta
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Happy to discuss the issue, inquisitive is a good and I know I have a lot to learn. Especially about Ohms.Hi, Hmm, I know what you mean so the following is written with an inquisitive tone, NOT an argumentative one. (being misunderstood has got me in trouble previously!)
In reality how long does the Cab battery sit at just 12.5V for? There's a SA on our car, I have a cheap voltage monitor plugged into the fag lighter and because it's a SA the voltage fluctuates a lot, however I've never seen it sit at 12.5v for any length of time, just for a few seconds after starting and that's it, it's then back up to typically much higher voltage than a resting fully charged hab battery and no current will flow from hab to cab.
12.6V is typical resting voltage for a fully charged LA battery, 12.8V suggests it's recently come off EHU and it's voltage is still naturally falling to 12.6v anyway so the voltage drop you saw could have been that? Maybe your fridge was on/set to auto and the voltage at the Cab bat (even though it was higher than 12.6V) wasn't high enough to keep up with demand considering the wiring resistance?
Even if it WERE possible:
12.6V hab battery connected to a 12.5V cab bat give a potential difference of just 0.1V. 0.2 ohms wiring resistance (I'd guess it's be more but let's go with that) gives just 1/2 an amp of discharge current falling to zero when the cab batt reaches 12.5V
I know there are issues with SAs and hab battery charging but I genuinely cant see (at the moment) how a hab battery could get significantly discharged by one.
Merl
When I was first exploring why my leisure battery was losing charge on journeys I read that with a smart alternator the engine battery voltage might be held as low as 12.3V. This was to leave room for energy recovery by the alternator when slowing down. I also understood that my fully charged leisure battery should have a resting voltage of 12.6V. I started to wonder if the split charge relay might be levelling the two battery banks. Wiring resistance got mentioned but with with Hymer‘s 50A fuse and chunky wiring I thought it wouldn’t be big factor. At the time (2017) I was also thinking about LiFePO4 and so I bought the B2B realising the problem might get worse with Li voltages. I upgraded both at the start of 2018 and everything worked well thereafter.
Chrisinchip
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Thanks for the reminder. For general info, the Sargent EC155 manual gives suggested wiring diag for using EC155 with B2B.
Sargent's recommended diag retains the D+ input to manage compressor fridge power supply if I recall correctly.
I'll still check out the Ablemail AMC.
Surely passive cooling does not obviate the need for siting in a ventilated space to avoid overheating? My intuition says that efficiency is key to keeping cooling, and therefore ventilation, to a minimum. Happy to be called out on this!
That wardrobe would take up a 1/3rd of my van
I'm going to take a look at Vitron kit. Thank you.
wildebus
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Their wiring suggestion would of course work. The D+ would still be active but the split relay would not do anything as the Starter Battery is not connected.
One reason why they would not suggest D+ disconnection into the EC155 is it would stop the Hab electrics all turning off when you run the engine. (for me, disabling that feature is a bonus!)
The D+ would not have anything to do with using a Compressor Fridge - that would run off the Leisure Battery always. A 3-way fridge operates in conjuction with the D+ as the 12V Powerr is passed to it via a relay controlled by D+, but this is not within the EC155 though. The only fridge related connection in the EC155 is the permanent 12V line, which is a low current connection and can be used by 3-way fridge Electronics (rather than fridge Power).
always good to have ventilated cooling. The point about not having a fan is you don't have to have airflow specifically in front of any fan inlets or behind any exhaust extracts. so fitting positions have more options.
That wardrobe would take up a 1/3rd of my van
I'm going to take a look at Vitron kit. Thank you.
merl
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My analysis comes from a purely electronic background which will always be 100% accurate (it's Ohm's law NOT Ohms guide) providing I have ALL the significant factors to take into account. I have quite a bit of knowledge of MH and vehicle electrics but nowhere near as much as someone like David (Wildbus). I've got a decent idea of what a smart alt is trying to achieve, I'm no expert wrt them so I cant be 100% certain how they'll react to every particular circumstance. They obviously make choices based on voltage but as to sensing current, temperature, time etc and how this is built into their equations and choices well who knows and I'd guess that varies depending on tech age and manufacturers programming choices.
From what I've read many with smart alternators struggle with their hab battery. I guess this is because the alt voltage typically sits below the usual 14.4v of a standard alt to save engine drag and then if/when regenerative breaking kicks in the voltage jumps up dramatically and gives the cab bat a massive kick of charge and as you suggest the wiring resistance means the hab battery doesn't get a decent share of that power.
merl
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Cheers Okta
When you say "your battery was losing charge" how did you come to that conclusion? How much charge? Could it simply be either/both of the situations I mentioned above?
I think you've hit on an incredibly important 'unknown' here and that's the total resistance in the charging circuit between the 2 batteries. I suspect it's higher than I/you'd expect and almost governs what's going on, both in the situation we're discussing now and also regarding the hot potato of 'drop in lithium' too. I've estimated it at a couple of tenth's of an ohm but I could be way out depending on cable gauge, length, fuse value/number/contacts/pcb tracks/connector type and how many and earthing arrangement. At tens of amps it has a significant skew in the outcome.
Maybe David could chip in here? Can't image he's ever took a resistance reading as he'd have no real need but he'll have a decent idea re cable sizes and run lengths as well as all of the above and how they differ from model to model.
Good subject BTW
merl
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shhh, he's still sleeping
!