Still struggling to understand how it all works! (1 Viewer)

[suavecarve]

We have two electric bikes and so far we have used aires and campsites with ehu when we have needed a charge for them.

That would change my thinking towards Lithium just for charging purposes.
It may depend upon how many times you charge your e bike battery and how much charge is required.

 

[suavecarve]

To give you some idea you could get a fogstar 100 ah lithium battery for £219 and may be entitled to 10% off if that is not the sale price.

That would give you twice as much battery bank as you have at the moment.

At the moment your solar panel is charging 100 ah succesfully and it will continue to do so.

As long as you dont need shed loads for your ebikes, I would just be swapping it for 100 ah lithium

 

[autorouter]

I’m guessing that they are attached in series as one wire goes to the negative on the left, two wires to the solar panel in the middle and one wire to the positive on the right.

I think that's just an effect of the camera angle. My take is pos and neg to Battery1, pos and neg from solar panel, and nothing to Battery 2.

Note that there are two methods of charging the leisure battery from the alternator while the engine is running. The traditional way is to use a relay to connect the leisure battery directly to the starter battery, so that the alternator charges the two batteries. When the engine stops, the relay disconnects the leisure battery from the starter battery and alternator. That relay splits the alternator charge between the two batteries, so it's called a split charge relay.

The second method is to use a proper DC-DC battery charger. It takes power from the alternator while the engine is running, and converts the alternator voltage into exactly what the leisure battery needs. A DC-DC charger is also called a Battery-to-Battery (B2B) Charger, or Charge Booster.

A split charge relay doesn't work very well with a smart alternator, and usually doesn't work too well with lithium either. So A B2B is a good upgrade for standard lead-acid batteries, but an essential upgrade with a smart alternator and/or lithium.

With a smart alternator, the B2B takes power from the alternator in just the same way as the lights, wipers etc. The smart alternator may drop its voltage from 14V down to say 12.6V, to avoid charging the starter battery. However the B2B can still take enough power at 12.6V to fill the leisure battery.

The two charging methods are not compatible, so if fitting a B2B, the split charge relay function has to be disabled somehow. Usually there are simple methods to do this.

 

[Purrfecttune]

I think that's just an effect of the camera angle. My take is pos and neg to Battery1, pos and neg from solar panel, and nothing to Battery 2.

Note that there are two methods of charging the leisure battery from the alternator while the engine is running. The traditional way is to use a relay to connect the leisure battery directly to the starter battery, so that the alternator charges the two batteries. When the engine stops, the relay disconnects the leisure battery from the starter battery and alternator. That relay splits the alternator charge between the two batteries, so it's called a split charge relay.

The second method is to use a proper DC-DC battery charger. It takes power from the alternator while the engine is running, and converts the alternator voltage into exactly what the leisure battery needs. A DC-DC charger is also called a Battery-to-Battery (B2B) Charger, or Charge Booster.

A split charge relay doesn't work very well with a smart alternator, and usually doesn't work too well with lithium either. So A B2B is a good upgrade for standard lead-acid batteries, but an essential upgrade with a smart alternator and/or lithium.

With a smart alternator, the B2B takes power from the alternator in just the same way as the lights, wipers etc. The smart alternator may drop its voltage from 14V down to say 12.6V, to avoid charging the starter battery. However the B2B can still take enough power at 12.6V to fill the leisure battery.

The two charging methods are not compatible, so if fitting a B2B, the split charge relay function has to be disabled somehow. Usually there are simple methods to do this.

Hi Autorouter

Thank you for such a clear description which now gives me greater understanding.

And you are right, on closer examination the second battery terminals on the solar control are not in use, it was just the camera angle.

Despite this, the Sargent control panel definitely shows solar charge alternately to both batteries so how it does that is a mystery!

I suppose that the unused, 2nd battery terminal on the solar control unit could be used for something additional (not sure what).

Based on this, I have had another thought:
In the manual for my solar control unit, it says that you can adjust the divert between the two batteries and that the factory preset is 50/50% (which it was).
Internet research suggests that a better split is 90/10% in favour of the leisure battery as the vehicle needs very little charge while stationary.
If battery terminal 2 is not in use, theoretically I can set it to 100/0% in favour of the leisure battery. However, erring on the side of caution, I have set it to 90/10% and will monitor the situation.

Still learning

 

[Purrfecttune]

On another motorhome thread about the same situation in 2018, one of the posters has said the same, that it is only set up for one battery. To also charge the starter motor battery, they said that a ‘battery master’ would have to be connected to the hab battery then the starter motor battery.

Mystery solved maybe?

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[autorouter]

Based on this, I have had another thought:
In the manual for my solar control unit, it says that you can adjust the divert between the two batteries and that the factory preset is 50/50% (which it was).
Internet research suggests that a better split is 90/10% in favour of the leisure battery as the vehicle needs very little charge while stationary.
If battery terminal 2 is not in use, theoretically I can set it to 100/0% in favour of the leisure battery. However, erring on the side of caution, I have set it to 90/10% and will monitor the situation.

I don't know about this particular model, but most of them automatically send 100% of the solar charge if only one battery is connected. In that case the percentage split setting has no effect.

 

[autorouter]

To also charge the starter motor battery, they said that a ‘battery master’ would have to be connected to the hab battery then the starter motor battery.

There are various ways to get around the problem of the starter battery gradually losing charge, if you park up for a week or more. A dual solar controller is a good option, but obviously only works when solar power is available.

The other option is a 'battery maintainer', which trickle-charges the starter battery from the leisure battery. Note, that's the opposite to a B2B, which gives a powerful charge from the alternator/starter battery to the leisure battery when the engine is running. There are various makes of battery maintainer, a favourite on here is the VanBitz BatteryMaster, but Ablemail, CBE, Votronic, Schaudt and others also do battery maintainers

The advantage of a battery maintainer is it trickle-charges the starter battery even when the leisure battery is being charged by the mains charger, not just from solar.

 

[RogerIvy]

Various people have given some spot-on advice.

The question that kept popping up in my mind was about the possibility of a DC-DC (B2B) already installed, thereby reducing the cost of upgrading to lithium. TBH this would be unusual with a Sargent system, they almost always come with a split-charge approach. The split-charge is usually in the Sargent unit itself (sometimes an external relay). We always look for evidence of a B2B which could reduce the cost of a lithium upgrade. Anyway .... get to that later.

My own observation having spoken to many people wanting to upgrade is that the biggest problem with lead acid (and gel/AGM) seems to be that it's complete guesswork as to how much is left in the tank. A SmartShunt goes some way to solving this but only if the battery(or batteries) are in good condition. The vast majority of control panels go by voltage to show battery health - and even a dud battery may show a "high" voltage for a short time. Folk go to bed with with 12.5v and wake up when the heating goes off. Basically it comes down to guesswork and uncertainty.

The situation I described above clearly does not apply to everyone, but it certainly is a common denominator in many discussions I've had.

One of the nicest things about the move to lithium is the BMS .... being able to see a reasonably good indication of true state of charge. Even if you replace like-for-like storage (a single 105ah lithium for 2 x 100ah FLA), it's grand to remove the guesswork so you can plan your trip.

OK, waffle over, to address some of the specifics mentioned already:
Your solar controller has only two wires coming out, so in theory connected to only one battery. There may be mechanisms in place to charge one battery then the other. Or to give you the ability to choose which battery to charge.
Given that you have a Sargent system you most likely don't have a DC-DC (B2B)
If you don't have a DC-DC and you have a smart alternator the only way to install lithium is to install a DC-DC charger.

If it was me I'd install a 230ah or 105ah lithium and a DC-DC (B2B) charger (assuming you don't have one). The 105ah is great for an upgrade from a single lead acid battery. The 230ah (and bigger) is a game-changer, totally changing the way you motorhome. As a frugal user (as someone described you earlier) you'd be able to spend several days at a nice camping spot even if there wasn't much solar yield.
If you like to know what solar yield you have changing to a Victron MPPT is a good idea, enabling you to use the app. If you aren't bothered to know, then stick with the controller you have.

My last comment would be: I've never personally come across anyone that regretted upgrading to lithium.

Are you passing though Oxfordshire so we can see what you have in your van?
... or going to a show?

 

[LostInSpace]

To the OP.

I think it is established that you have a smart alternator, but this can be confirmed by plugging a voltmeter device into the cigarette lighter socket (powered by the engine battery). If the reading goes up and down as you drive, then you have a smart alternator; i.e.
- 12ish volts when you are 'driving'
- 13ish volts on engine overun.
- 14ish volts when breaking.

If you do have a smart alternator, then repeat the same thing with a voltmeter on the leisure battery. If the volts stay sustantially constant the you have a B2B.
If you are lucky, to simplify the job, you may even have a cigarette lighter socket in the back of the 'van powered off the leisure battery. Ours does.

---------------------------------------

IF you do have a B2B, then the task of changing to lithium is so much simpler. Just change the settings on the three chargers.

To me, the biggest advantage of lithium, is all that extra usable power with a reduction in battery weght.

 

[Purrfecttune]

There are various ways to get around the problem of the starter battery gradually losing charge, if you park up for a week or more. A dual solar controller is a good option, but obviously only works when solar power is available.

The other option is a 'battery maintainer', which trickle-charges the starter battery from the leisure battery. Note, that's the opposite to a B2B, which gives a powerful charge from the alternator/starter battery to the leisure battery when the engine is running. There are various makes of battery maintainer, a favourite on here is the VanBitz BatteryMaster, but Ablemail, CBE, Votronic, Schaudt and others also do battery maintainers

The advantage of a battery maintainer is it trickle-charges the starter battery even when the leisure battery is being charged by the mains charger, not just from solar.

Thanks again Autorouter, very helpful.
And again, you are right. Having studied the manual very closely again, it does state that if only one battery is connected it receives 100% charge regardless.

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[Purrfecttune]

To the OP.

I think it is established that you have a smart alternator, but this can be confirmed by plugging a voltmeter device into the cigarette lighter socket (powered by the engine battery). If the reading goes up and down as you drive, then you have a smart alternator; i.e.
- 12ish volts when you are 'driving'
- 13ish volts on engine overun.
- 14ish volts when breaking.

If you do have a smart alternator, then repeat the same thing with a voltmeter on the leisure battery. If the volts stay sustantially constant the you have a B2B.
If you are lucky, to simplify the job, you may even have a cigarette lighter socket in the back of the 'van powered off the leisure battery. Ours does.

---------------------------------------

IF you do have a B2B, then the task of changing to lithium is so much simpler. Just change the settings on the three chargers.

To me, the biggest advantage of lithium, is all that extra usable power with a reduction in battery weght.

Thanks LostInSpace, this is also helpful.
I have a device already plugged into the lighter socket that feeds a bank of usbs for charging when on the move and it has a voltage read-out on it. I do also have a lighter socket in the hab area so could try what you’re suggesting.
However, I think that Rog is correct and I will likely pay him a visit in a couple of weeks or so to confirm.

 

[Purrfecttune]

Various people have given some spot-on advice.

The question that kept popping up in my mind was about the possibility of a DC-DC (B2B) already installed, thereby reducing the cost of upgrading to lithium. TBH this would be unusual with a Sargent system, they almost always come with a split-charge approach. The split-charge is usually in the Sargent unit itself (sometimes an external relay). We always look for evidence of a B2B which could reduce the cost of a lithium upgrade. Anyway .... get to that later.

My own observation having spoken to many people wanting to upgrade is that the biggest problem with lead acid (and gel/AGM) seems to be that it's complete guesswork as to how much is left in the tank. A SmartShunt goes some way to solving this but only if the battery(or batteries) are in good condition. The vast majority of control panels go by voltage to show battery health - and even a dud battery may show a "high" voltage for a short time. Folk go to bed with with 12.5v and wake up when the heating goes off. Basically it comes down to guesswork and uncertainty.

The situation I described above clearly does not apply to everyone, but it certainly is a common denominator in many discussions I've had.

One of the nicest things about the move to lithium is the BMS .... being able to see a reasonably good indication of true state of charge. Even if you replace like-for-like storage (a single 105ah lithium for 2 x 100ah FLA), it's grand to remove the guesswork so you can plan your trip.

OK, waffle over, to address some of the specifics mentioned already:
Your solar controller has only two wires coming out, so in theory connected to only one battery. There may be mechanisms in place to charge one battery then the other. Or to give you the ability to choose which battery to charge.
Given that you have a Sargent system you most likely don't have a DC-DC (B2B)
If you don't have a DC-DC and you have a smart alternator the only way to install lithium is to install a DC-DC charger.

If it was me I'd install a 230ah or 105ah lithium and a DC-DC (B2B) charger (assuming you don't have one). The 105ah is great for an upgrade from a single lead acid battery. The 230ah (and bigger) is a game-changer, totally changing the way you motorhome. As a frugal user (as someone described you earlier) you'd be able to spend several days at a nice camping spot even if there wasn't much solar yield.
If you like to know what solar yield you have changing to a Victron MPPT is a good idea, enabling you to use the app. If you aren't bothered to know, then stick with the controller you have.

My last comment would be: I've never personally come across anyone that regretted upgrading to lithium.

Are you passing though Oxfordshire so we can see what you have in your van?
... or going to a show?

Hi Rog

Finally after a very long time and several headaches I think I now fully understand Solar, B2B and batteries thanks to everyone’s input and finally yours, which is very concise.

I have sent you an email in response

 

[Tombola]

Not sure on your budget, but if you are going mppt anyway then go even as small as 100ah lithium, ideally then also a b2b.
You'll get more bang for your buck in the long run.

Lead acid will have had its day soon

 

[Carpmart]

Simple solution.
I have one of these.

A telescopic truck screen squeegee with a swivel head.
Cost £10 in Germany a couple of years ago.

Every few days I stick my head out of the rear roof vent and wipe down the solar panel.
It can almost double our solar input!


View attachment 934335

Interesting how advice and recommendations vary.

I do clean my panels occasionally but in my experience, it makes zero difference to output unless you have red Saharan sand or bird poop all over them.

The screen squeegee is absolutely the tool for the job, assuming you do bother to clean them!