Will I really need a DC to DC charger?

dally

dally

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Hi, We're going to go the lithium route next time I replace our lead acid batteries. So far I've upgraded our solar to get ready for the switch. I have 300watts solar connected to a Victron smart solar 100/75, which is charging 3 x 110amp batteries. I have a Schaudt EBL which doesn't have a Lithium charging profile, so I'll by pass that with one that does. I also have a Van Bitz battery master. We don't have an inverter and I can't see us needing one so our energy needs are pretty low.

So all that's left is charging from the alternator. Do I need it? The van is stored outside so the batteries are full from solar when setting off.

We did 5 weeks stationary in Spain with the on board charger disconnected earlier this year and the batteries were always full according to the shunt.

We have just done a weeks rally with no problem and a 4 day rally in poor weather, again without a battery issue. Do I really need to spend money on a DC to DC charger? Am I missing something?
 
You clearly do not need it…

However, my approach is layers of redundancy and options, so I personally would still opt for one.
 
If you want to charge a lithium battery from the engine alternator while driving, you need a B2B charger. However if you think you don't need to do that, then you can skip installing one, but either way you need to disable the split charge relay so that it doesn't connect the lithium battery in parallel with the starter battery.

Some people on here are reporting that some motorhome manufacturers have the same idea, and are avoiding the whole problem by not fitting a B2B or split charge relay, and telling the customer to charge from hookup or solar. Obviously they don't put that front and centre of their sales pitch, but it's in the manual small print.
 
If you are staying for five weeks in one place, a DC to DC charger won't do anything. Unless you have a heavy load requirement such as an inverter, do you really need lithium?
 
I would put the B2B before the mains charger. When on hook up you don’t need a full battery, just choose a setting that under charges. With solar you will get topped up anyway. The B2B not only makes sure you arrive with a full battery it provides protection for the alternator, a flat LiFePO4 battery can be very greedy.
autorouter said:
If you want to charge a lithium battery from the engine alternator while driving, you need a B2B charger. However if you think you don't need to do that, then you can skip installing one, but either way you need to disable the split charge relay so that it doesn't connect the lithium battery in parallel with the starter battery.

Some people on here are reporting that some motorhome manufacturers have the same idea, and are avoiding the whole problem by not fitting a B2B or split charge relay, and telling the customer to charge from hookup or solar. Obviously they don't put that front and centre of their sales pitch, but it's in the manual small print.
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Cheapskate manufacturers being lazy or greedy?
 
cyberyacht said:
If you are staying for five weeks in one place, a DC to DC charger won't do anything. Unless you have a heavy load requirement such as an inverter, do you really need lithium?
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Agree with this. If you are a low energy user and your current lead acid batteries manage with your current pattern of usage, I'd question the need for lithium, nevermind a B2B charger.
 
Thanks for the replies. I'm just thinking ahead here to be honest. I'm not going to change until I have to. Weight is as much a consideration as anything when I do change and also a new Lithium will probably do us until we're done.
 
If you can manage 4 days in bad weather, off grid, on roughly 150 amp hours plus a bit of solar gain (assuming lead acids discharged to around 50%) - would I be right to assume you run your fridge on gas ?
 
cyberyacht said:
Unless you have a heavy load requirement such as an inverter, do you really need lithium?
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As above.
You say your usage is low so why buy expensive lithium, or is it a case of "I have lithium" bragging rights.

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Ernesto said:
If you can manage 4 days in bad weather, off grid, on roughly 150 amp hours plus a bit of solar gain (assuming lead acids discharged to around 50%) - would I be right to assume you run your fridge on gas ?
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yes, off grid so gas for the fridge.
 
pappajohn said:
As above.
You say your usage is low so why buy expensive lithium, or is it a case of "I have lithium" bragging rights.
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No bragging rights here. It's as I said earlier, weight, 3 x 110amp lead acid against one Lithium and if we, lets say, get another 12 or 13 years from motorhoming, bearing in mind we haven't changed batteries yet, then one long lasting Lithium battery might see us through.


My question was more about weather I needed a B2B charger with my type of usage as and when we change to Lithium. It just seemed as tho one followed the other and I wondered if there was something I wasn't quite getting. (y)
 
dally said:
No bragging rights here. It's as I said earlier, weight, 3 x 110amp lead acid against one Lithium and if we, lets say, get another 12 or 13 years from motorhoming, bearing in mind we haven't changed batteries yet, then one long lasting Lithium battery might see us through.


My question was more about weather I needed a B2B charger with my type of usage as and when we change to Lithium. It just seemed as tho one followed the other and I wondered if there was something I wasn't quite getting. (y)
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I don’t think you’re missing anything …you are so unusually frugal with electricity, it doesn’t seem necessary.
 
As Pausim says not worth the risk with Lithium always fit a B2B, a burnt out alternator will cost you a lot more and with a B2B the battery will get the correct charge.
"Drop in Replacement" is marketing BS IMO.
 
We’ve done a number of tests connecting 100AH, 230AH, 280AH and 304AH batteries directly to a few different alternators (none of them Euro6).

We did this because of the growing number of battery sellers stating their battery is a drop-in replacement. We never said this of ours because we were nervous that our batteries could blow electrics and/or fry the alternator.

In a nutshell we’re willing to tell potential customers that our 100AH could be a drop-in replacement because the most it ever drew was 37A for a very short time and then dropped to below 30A. But even then we tell people that we’d need to test if their particular vehicle is OK. Quite a number of people already have two lead acids so the only real saving would be weight for the same power storage. But … I’m happy to tell someone that our OPS100 (100AH) probably doesn’t absolutely need a DC-DC charger as long as it’s accepted that it may likely never get to 100% SOC, but only after testing. Still prefer a DC-DC though.

The other batteries we say are NOT drop in replacements because they had a peak draw of over 50A which could be too much for the alternator but more importantly for the EBL and wiring. Might be OK for some vehicles, but again only after extensive testing and with the usual caveats.

Just to be clear: we still prefer installing a DC-DC because the battery generally does better (charged at the exact voltage it needs and gets to 100% SOC) and the BMS moves from being the only line of defence to the last line of defence. When I say 100% SOC I generally mean a voltage of 14.2 which is the Victron default. 14.6v should only be used once if you’re top balancing (cells to 3.65v) or doing a one-time capacity test.

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The thing Ive found I use least is the mains charger, Solar and Alternator seem to cope with most of our use, although we dont spend much time stationary in UK.

We're Hybrid 220ah Gel and 200ah LiFePo4 in paralel. No B2B
 
autorouter said:
If you want to charge a lithium battery from the engine alternator while driving, you need a B2B charger. However if you think you don't need to do that, then you can skip installing one, but either way you need to disable the split charge relay so that it doesn't connect the lithium battery in parallel with the starter battery.

Some people on here are reporting that some motorhome manufacturers have the same idea, and are avoiding the whole problem by not fitting a B2B or split charge relay, and telling the customer to charge from hookup or solar. Obviously they don't put that front and centre of their sales pitch, but it's in the manual small print.
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our lithium batteries charge from the split charger solar and ehu none of which have litium settingsand havent let us down in 4 years weve had them
 
We have 700 watts of solar a Victron 12/2000/80 inverter charger and 2 x 100 amp Transporter batteries. The other day I left the hab aircon on and ran the batteries down to 15% later went for something to eat the charge rate from the alternator peaked at 1123 amps we do not have a B2B
 
Bessy765 said:
We have 700 watts of solar a Victron 12/2000/80 inverter charger and 2 x 100 amp Transporter batteries. The other day I left the hab aircon on and ran the batteries down to 15% later went for something to eat the charge rate from the alternator peaked at 1123 amps we do not have a B2B
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Did the alternator melt?
 
93 amps, system been working for over 3.5 years, warranty for 5 years, only proviso is don’t run the engine just to charge the batteries for more than 15 mins. Plus uprated wiring
1695821302980.jpeg
It
 
Pausim said:
Or perhaps Watts.
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This was the output from my alternator with a little help from solar whilst driving at around 50 mph with the hab air on. The minus sign on the DC power is actually the charge from the alternator rate of charge

1696235007367.png
 
That's a hefty amount you're pulling from your alternator!
 
Bessy765 said:
This was the output from my alternator with a little help from solar whilst driving at around 50 mph with the hab air on. The minus sign on the DC power is actually the charge from the alternator rate of charge

View attachment 817253
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that is watts not amps, volts x amps = watts. 1000 amps would have melted stuff

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Depends how you use it. Winter time solar doesn't pull much. I never use hookup so a b2b is a neccesity for me.

I've 400watt solar ,105ah lithium and a 40amp b2b.

Don't use campsites and don't want to rely entirely on solar.
Vans old enough I can run engine when idle for hours if i need to without it doing any damage.
 
mitzimad said:
our lithium batteries charge from the split charger solar and ehu none of which have litium settingsand havent let us down in 4 years weve had them
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Steve, can I ask what settings you were advised to charge your Lithiums on please? Some say LA, whilst others say Gel. 🤷‍♂️
My 60A B2B has a Lithium setting, so 100% charge would be achieved periodically.

Cheers,

Jock. :)
 
1123W at 12V is 1123/12 = 93A.

The picture shows 1098W from the alternator and 105W from the solar (= 1103W total), being used by the a/c (923W) and the charger (113W) making a total usage of 1063W. So apart from 35W of losses, it all adds up.
 
Yes the alternator is rated at 150 amps and all cabling is heavy duty, if we were in heavy traffic or climbing hard I turn the hab air off to reduce the load it’s only on when needed. Been running this setup for over three years and 20,000 miles not had ehu since. The company who fitted the system warrant the installation for 5 years the batteries for ten. As we do not have a smart meter a B2B is not required.
 

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