#153272  by NeilV
 Tue Jul 23, 2019 6:24 pm
Thanks for the replies!

I did think about adding a resister, as Ohms law says 28v / 0,56Ohms =50A... but I wasn’t sure what that would do to the alternator itself?

Would that limit the alternator to WORK less to produce the 50A, or work flat out to overcome the resistance?

Thinking about SLA’s I’d say if the resistance increases the voltage regulator on the alternator will slow down its load... but not sure where the (nominal) heat OF the resistance would get its energy then? 🤷‍♂️

I know just enough to understand what’s being suggested by each of you, but not enough to know what the effect on the alternator would be (my primary concern).

65A to the LifePo4 won’t hurt it, but alternator running flat out might?
 #153274  by scubadoo
 Tue Jul 23, 2019 6:53 pm
NeilV wrote:
Tue Jul 23, 2019 6:24 pm

...I did think about adding a resister, as Ohms law says 28v / 0,56Ohms =50A... but I wasn’t sure what that would do to the alternator itself?
By tiny resistance I mean a length of suitable wire. A 0.56Ω resistor would likely glow red hot then self destruct very quickly. :shock:
We are not talking about 28V Neil but the voltage drop along the length of wire at a given current.
1m of 8 gauge copper wire has a resistance of about 0.002Ω.
NeilV wrote:
Tue Jul 23, 2019 6:24 pm
...Would that limit the alternator to WORK less to produce the 50A, or work flat out to overcome the resistance?...
Yes and no.
 #153275  by NeilV
 Tue Jul 23, 2019 7:47 pm
:x
scubadoo wrote:
Tue Jul 23, 2019 6:53 pm
NeilV wrote:
Tue Jul 23, 2019 6:24 pm

...I did think about adding a resister, as Ohms law says 28v / 0,56Ohms =50A... but I wasn’t sure what that would do to the alternator itself?
By tiny resistance I mean a length of suitable wire. A 0.56Ω resistor would likely glow red hot then self destruct very quickly. :shock:
We are not talking about 28V Neil but the voltage drop along the length of wire at a given current.
1m of 8 gauge copper wire has a resistance of about 0.002Ω.
NeilV wrote:
Tue Jul 23, 2019 6:24 pm
...Would that limit the alternator to WORK less to produce the 50A, or work flat out to overcome the resistance?...
Yes and no.
:lol: 28v is the alternator default output. Will have to try the longer thinner cable to induce voltage drop, but since I will have the AGM starters in parallel, theoretically all I have to do is match their resistance to make it an equal charge system 🤔
 #153276  by scubadoo
 Tue Jul 23, 2019 8:04 pm
What is the highest voltage measured at the terminals of your start battery(s) after a long drive and the motor still running at fast idle speeds? That number has relevance. 27.4 - 28.4V would be OK for me.
Have you ordered the Victron Batteryprotect device? If so I'm guessing it will solve most if not all of your concerns.
It was that easy for me. Set and forget.
 #153280  by markcraven
 Wed Jul 24, 2019 5:31 am
Just for information. I was also worried about alternater charging and what had been said on other forums. I first bought a DC-DC charger to protect it but was only charging at 40A from a 60A rated unit. I decided to give the direct connection approach with a battery isolator. I have a 200Ah lithium with a 120A alternator on my Land Rover. Turned the key (fingers crossed) and had my hand on the isolator it ran at initial 100A for a few minutes then dropped to 80A. Was happy with that at a 30% SoC. It then tails off as the battery fills like a LA but not as quickly. When nearly full it's still putting in 15-20A. I have aJunsi cell logger and when it reaches 14V or cell differential reaches 150mV turn the switch off. I am the BMS :TU
 #153283  by NeilV
 Wed Jul 24, 2019 12:36 pm
Thanks. With a decent solar setup, I’m hoping alternator charging will be ‘as and when’ for the lithium and I currently plan to have a 50A fuse on one side of the DVSR so it can be isolated, and will even trip if I start pumping it too hard and somehow forget they’re connected.
Since the DVSR is ‘already there’ I’m thinking to leave it on the lithium side of the 50A isolator, and have a light on a ‘normally closed’ relay to tell me when the LifePo4 hits the DVSR cutoff voltage of 25.6 (approx 30%) and I might need to use the alternator to charge it anyway (and before either the BMS or the battery protect cuts it all off at 24v too!)
 #153284  by NeilV
 Wed Jul 24, 2019 12:54 pm
scubadoo wrote:
Tue Jul 23, 2019 8:04 pm
What is the highest voltage measured at the terminals of your start battery(s) after a long drive and the motor still running at fast idle speeds? That number has relevance. 27.4 - 28.4V would be OK for me.
Have you ordered the Victron Batteryprotect device? If so I'm guessing it will solve most if not all of your concerns.
It was that easy for me. Set and forget.
My alternator drops to 27.8 when the battery (AGM) is full from the solar and I drive for more than 1/2 hour so not a worry there either as the ‘full’ voltage for the cells I’m getting is 27.2 and the given ‘charge’ voltage is 29.2 :TU
Just going to use the isolator at either 50a or 60a to protect the alternator from going full tilt for hours.

I’m sure once I get it all set up I’ll tinker for a few weeks and then just ‘set and forget’ (once it’s calibrated) too :TU
 #153461  by NeilV
 Sun Jul 28, 2019 9:25 am
Ok, quick update for those interested...
My cells arrived safely, but were slightly out of balance, so I fitted the HA02’s in the sets of 4 and the squeezed away gently for the night while I did some other wiring tweaks that needed doing. Next morning the two different sets were 0.12v (HA02 can only do 4 cells in series, or more in parallel as they self balance too) so I series the cells in groups of 4 (12v) and then paralleled the two 12v sets for about 4 hours (we went out) all cells beautifully balanced at 3.337 when I returned, so I then fitted the final link to make an 8S 24v set. Adding the Dally BMS and the battery protect and reconnecting all my loads and the main house setup was sweet! :TU
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